STUDIES ON MARINE FAUNA, VOLUME XV (XXIII)
Nematodes and. Their Role in the — Meiobenthos
T. A. PLATONOVA V.V.GAL'TSOVA
Nematodes constitute a numerous and widely distributed group in world fauna. They inhabit seas, fresh waters, and soil. Many are parasites. Since representatives of the class Nematoda are numerous, their role in the national economy and the life of man is significant. Hence a comprehensive study of nematodes is well warranted. Nematodes are typical inhabitants of the benthos; their entire development and subsequent life cycle take place in benthic surroundings. Some namatodes, however, lead a pleustonic mode of life. Often nematodes are found in different types of overgrowths. The present work concerns related groups of free-living marine nematodes, which were earlier combined in the family Leptosomatidae (order Enoplida). The numerous and varied forms included in this family have long prompted taxonomists to split the family Leptosomatidae into several subfamilies, or to transfer some genera to other families of the order. Descriptions of 73 species of nema- todes detected to date in the seas of the Soviet Union, and included in 14 genera and 4 families, are presented in the taxonomic sections of this book.
mo Tinie?
ey,
Nematodes and Their Role in the Meiobenthos
TT 79-52000
AKADEMIYA NAUK SSSR Zoologicheskii Institut
ACADEMY OF SCIENCES, USSR Institute of Zoology
STUDIES ON MARINE FAUNA
[Issledovanie Fauny Morei]
VOLUME XV (XXIII)
Nematodes and Their Role in the Meiobenthos
[Nematody i ikh Rol’ v Meiobentose]
T.A. PLATONOVA and V.V. GAL’TSOVA
Nauka Publishers, Leningrad, 1976 Translated from Russian
Published for the Smithsonian Institution Libraries and the National Science Foundation, Washington, D.C., by Amerind Publishing Co. Pvt. Ltd., New Delhi
1985 .
© 1985 Oxonian Press Put. Ltd., New Delhi
Translated for the Smithsonian Institution Libraries, pursuant to an agreement with the National Science Foundation, Washington, D.C., by Amerind Publishing Co. Put. Ltd., 66 Janpath, New Delhi 110 001
Translator: Surendra Sharma General Editor: Dr. V.S. Kothekar
Printed at Printsman Press, Faridabad, India
Foreword
Nematodes constitute a numerous and widely distributed group in world fauna. They inhabit seas, fresh waters, and soil. Many are para- sites. Since representatives of the class Nematoda are numerous, their role in the national economy and the life of man is significant. Hence a comprehensive study of nematodes is well warranted.
Free-living nematodes have been studied very little compared to parasitic nematodes. Yet a study of the former is imperative considering the place they occupy in the biocenose. Nematodes live in almost every type of biotope in seas—pure and silted sands, silt and clay, shells and shingles. Many species of algae are infested by them; they are also found in hydroids, sponges, bryozoans, and other invertebrates. Nematodes have been found at various depths in seas—from the littoral zone to depths of several thousand meters (Ditlevsen, 1926).
Nematodes are typical inhabitants of the benthos; their entire devel- opment and subsequent life cycle take place in benthic surroundings. Some nematodes, however, lead a pleustonic mode of life (Steiner, 1922a). Often nematodes are found in different types of overgrowths. Free-living nematodes of marine biocenoses are reviewed by V.V. Gal’tsova (p. 215) in the present work.
Gal’tsova notes that due to their abundance, nematodes play a signi- ficant role in the trophic chain and breakdown of organic substances in the benthic community.
The study of free-living marine nematodes began in the 1860’s, cover- ing mainly the species composition, anatomy, and morphology of differ- ent species of this group. These works are too numerous to be listed here; relevant references are noted in the text at appropriate places.
The ecology, biology, and zoogeography of free-living marine nema- todes have received less attention than their systematics and morphology. Information regarding the geographic distribution of this group is, there- fore, negligible.
The ecology of nematodes has only recently attracted the attention of researchers, mainly in the last twenty years.
Filip’ev has made major contributions to the fauna of free-living nematodes in the seas of the Soviet Union. His published works cover
4 nematodes of the Black Sea (1918-1921, 1922a), nematodes of the order
Vi
Enoplida inhabiting the northern seas of the Soviet Union (1927), and two smaller works—one on nematodes of the Sea of Azov (1922c) and the other on nematodes of the Arctic Ocean (1946).
The present work concerns related groups of free-living marine nema- todes, which were earlier combined in the family Leptosomatidae (order Enoplida). The numerous and varied forms included in this family have long prompted taxonomists to split the family Leptosomatidae into sever- al subfamilies, or to transfer some genera to other families of the order.
Before discussing a revision of the family Leptosomatidae, it should be noted that two superfamilies must be distinguished in the order Enoplida —Leptosomatoidea and Enoploidea (p. 69). The families Leptosomatidae, Anticomidae, and Triodontolaimidae are included in the superfamily Leptosomatoidea and the other two families—Rhabdodemaniidae and Crenopharyngidae—included in the superfamily Enoploidea.
The inclusion of these five families in the order Enoplida means re- cognition of a significant number of primitive features within the limits of the order. Keeping this in mind, the present work discusses revision of Leptosomatidae from the old point of view, as well as revision of some lower families of both superfamilies of the order Enoplida.
‘Descriptions of 73 species of nematodes detected to date in the seas of the Soviet Union, and included in 14 genera and 4 families, are pre- sented in the taxonomic sections of this book.’’ The material comprised the authors’ personal collections from the Black, Barents, and Okhotsk seas, and the Sea of Japan; collections preserved in the Institute of Zoo- logy, Academy of Sciences of the USSR; and preparations of Filip’ev containing not only type specimens, but samples of other species describ- ed by him. More recent material includes specimens from the Barents Sea collected by E.F. Gur’yanova, P.B. Ushakov, and O.G. Kusakin, and specimens from the Kara, Laptev, Bering, and Chukchi seas collect- ed by P.B. Ushakov and G.P. Gorbunova. Material from Sakhalin and Kuril islands was also examined, which had been collected during the 1947 to 1948 Kuril-Sakhalin expedition organized by the Institute of Zoology, Academy of Sciences of the USSR. Lastly, M.N. Kiselova, a worker in the Institute of Biology of the Southern seas, kindly loaned us his collection of nematodes from that region.
We are very grateful to all the persons mentioned above whose mate- rial served as a basis for the present work.
We are further grateful to Yu.V. Mamkaev and Ya.I. Starobogatov for their friendly criticism during the writing of this work, and indebted to A.A. Strel’kov who edited the manuscript.
Contents
FOREWORD
LOWER ENOPLIDA OF THE SEAS OF THE SOVIET UNION—T.A. Platonova List of Species of Lower Enoplida of the Soviet Union Introduction Anatomy and Morphology Phylogenetic Relations and Taxonomic Basis Ecology Geographic Distribution Collection and Processing of Nematodes Systematics
References
FREE-LIVING MARINE NEMATODES AS A COMPONENT OF THE MEIOBENTHOS OF CHUPA INLET OF THE WHITE SEA ~V.V. Gal’tsova
Introduction Physical and Geographic Characters of the Region under Study Terminology, Material, and Methodology Quantitative Characters of the Meiobenthos of Kruglo’e Bay List of Species of Nematodes of the White Sea Taxonomic Review of Species
Quantitative Distribution of Leading Species of Nematodes in the Littoral Zone of Kruglo’e Bay
Influence of Important Factors on Living Conditions
and Population Dynamics of Nematodes Conclusions References
203
215 217
220 222
232 255 259
298
323 350 354
Lower Enoplida of the Seas of the Soviet Union
List of Species of Lower Enoplida of the Soviet Union
Class NEMATODA Subclass ADENOPHOREA
Order ENOPLIDA
1. Superfamily LEPTOSOMATOIDEA 1. Family LEPTOSOMATIDAE 1. Subfamily LEPTOSOMATINAE
1. Genus Leptosomatum Bastian, 1865
RET CHIC MUD CVs MONO 8 a8 oe oss 0) ier Sool olojeus eee csgeeheuenereatts SPSCOHICIC EIDE Vay OMG Hie ae aN fame naa Me Galea canal wbenringicumiurilipjyevs DLO. sng as ce scsi o oke cess suaciilatum (Eberthy T8653) oe a cece es obi \erenioneye ecloncatum Bastian, USGS oo. 0s weveretie «usu susteuaite oun eieile epUnctatiM (Eberth, NS63) i255): aie m= sien ses < Cospeve epeleuelaleueys Miciroplialmum: Saveltev, O12 ei cee rsp eee cael wunecpiceps Platonova, LOOT 2... oe cues oie als ciselels sepetaaies MOLUCHE BAStianl iSO sas ck ie kao dnt niet tales laelon. AP ea
WOON AAR YN alts esl test [eset tea tes! es)
2. Genus Leptosomatides Filipjev, 1918
10. bie 12. 13: 14. 1S. 16.
MCULINGL EMI PJEVs LOS. ise cee HK ue Shine eee ee PESECINE pe MIDJCVsh LODZ ee triers tn ace wee Gea lebe ah MNOCEHAtUSMPlAatOnOVaAN TOOT cet vce ee eee wanes 2 HCLASSUS PlATONOVAN LOOM Ne Melee els Marske aie ae lees 6 MACUTIDADINOSUS SPs MOVia eee soe ats ay Ee) an OL CUISCLOSUS SP MOV sjsieusials se sae a csiialei dusts veleie seis woes eee EIMLATII GE: SP). sTLOM = nisi o eis \o ibe te elie lo eee ouurte eyelet -usiers Meek ae tet
ts See ee eae
3. Genus Leptosomella Filipjev, 1927
17... acrocerca Filipjev, 1920... . 5. ae ee ee 100 2. Subfamily SYNONCHINAE 4. Genus Synonchus Cobb, 1893 182 Simurmanicus Pilipjev, 1927. .-. fe.o5. ee eee 103 5. Genus Anivanema gen. nov. 19) Almasha: sp. NOVA Ste E.R. Gd oe. oats Mow cio cane 105 3. Subfamily THORACOSTOMATINAE 6. Genus Deontostoma Filipjev, 1916 20: D: papillatum (Eimstow, 1903). 5. hs 2. eee 109 21. Ds arcucum (Saveliey., 1912). sr. sce a. ce ee eee 110 22: D. lobatumi(Steiner, 1916) 5 3 oe oe ee 112 7. Genus Pseudocella Filipjev, 1927 23. P.-trichedes (-eucart; 1849) =e. 2 Nee eee a ae 116 24: P. elegans: (Ditlevsen, 1926)... 37 cscs ae ee 118 25. P. saveljevi (Failipjevy: 1927). aidieninas. sesame «tae 5 eee 120 26. P; tenuis Filipjev, 1946. 2. oc. 2.6 ces ee ee eee ee 121 21. P.-coecum (Saveliev, 1912). os se se oie eae 123 23.-P. SraciliseSp, MOV. 250 koe ee oe oe ee Ee 124 29: Pespesudocellum (Filipjey, 1927) 5. 2.) oe eee 126 30.°P: bursata Platonova,- 1962: 3: 32 65 eo eee ee 126 31. P. minor’ Platonova; 196275322 32 eee ee oe cle eee 128 32° °P; kurilensis Platonova, 1962 )5....52. sce os ceo eee 129 33: P.mamillifera Platonova, 196277 3.0 8. 3 yee 132 B42: QCula. Sp: NOVAS. sd ASO ro eee 134 “UP. GNgusticeps SP: NOV... es a oe eo ees eee 135 36: P. truncaticauda sp: NOV... ... 5... vss eee eee 136 37. 0P. rarisetosa ‘SP NOV i 5 ee 2 cle i one cr eee 138 38i0P. raddde SP. NOV... 0. ode sea Koss oe cbs Ue bee ee ene 139 2. Family ANTICOMIDAE 4. Subfamily ANTICOMINAE 8. Genus Odontanticoma gen. nov. 39:40. dentifer Sp. NOV «5.2.5 605 sto. vio oon 6 © se Se oe eee 143 40: O} murmanica (Filipjev, 1927) .....0. 2. oc.) oe 2 eer 145
58.
Sys
60. 61. 62.
63. 64.
AS RA RRR RAR AAR AD Db
9. Genus Anticoma Bastian, 1865
eDentin Bastian 865% 2/4L SS ORO NT HOP ar . insulaealbae Filipjev, 1927 . minor Filipjev, 1927 . arctica Steiner, 1916 LiMALISHBAStiAMs US OS es ccs cisco: Weesneg hc pdb seis ete deel vats ban pellucida Bastian, W865 - = oii. 5 Sages spouesayde opto she icioustorest novozemelica (Filipjev, 1927) brevisetosa Platonovan 1967... 3 Spats ensucsepccotenehe loc eeoir MELD CUIPMALONOV ay PICT oye voxare wept vo cel hota anes aha oapeleestons tenuicaudatoides Gerlach and Riemann, 1974 grandis Platonova, 1967 behringiana sp. nov BUGEABS |) SOTO VEG sychsince Sedan tyes Sane MR ha Magia ved 8 sp aninte uschakovi sp. nov PRAGCI{UCOSS Ie, TOV Sen Sectors. aeenaico bi aye alles Sia latene! Suakiouaserei/ece Se Hotes 6! BOORMCOIMMP ICV scl ONS i sara Css) a wy ghee Heim ic eiee Staten . platonovae Sergeeva, 1972
Ce ey er er}
ec eeees ee eee ee ee we ee oe eo 8
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eoeeeee ee ee ee ee oe ee ee ow wo ee oo ow
2 er 7
5. Subfamily PLATYCOMINAE 10. Genus Platycomopsis Ditlevsen, 1926 P. mesjatzevi (Filipjev, 1927)
eooeeeeee cece eo ee ee ee wore eee eee
6. Subfamily BARBONEMATINAE 11. Genus Barbonema Filipjev, 1927 B. setifera Filipjev, 1927
oe ee ee eee eee eo eee oH ooo Hoe ooo eee
2. Superfamily ENOPLOIDEA 3. Family CRENOPHARYNGIDAE fam. nov. 12. Genus Crenopharynx Filipjev, 1934
C. marioni (Southern, 1914) C. gracilis (Linstow, 1900) C. armatus sp. nov
eoeesr ec eee eee ee ee eee we eo ee ew Ooo sec eeee ee ec eco eee eee oe oe ee eo eee oe
eoeeeeee eee ee ee eo eo ee eee eo ooo ee eo owe ewe
13. Genus Nasinema Filipjev, 1927
N. polare (Steiner, 1916) N. boreale sp. nov
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eoeceeeo eee eee ee eo ee ee eo wm oem om ome wow eo 8
by wD wD yD
4. Family RHABDODEMANIIDAE 14. Genus Rhabdodemania Baylis and Daubney, 1926
vminor (Southern, 1904) ho) es cee ogee nee eer 192 — ) eracilis\ (Ditlevscm, 19) secession erty ale dhs -edentulaPlatonovar NOTA oo eee ae ae ees ae 194 latifaux Platonovas 974 wie ce we eres ct ie nae 196. “hexonchia Platonova, (974 oe an 5 ee ee 197
pontica’ PlatonovayVOGS ys ess aes ee 198
“marisalbrPlatonova 1974 oa ian ee cree lee eee 199
orientalis: Platonovar lO Taio once cee aie ase Ce 200 aneustissima Platonova; 19745. oo. es hee 201
8
Introduction
ANATOMY AND MORPHOLOGY
Size and shape of body. As a group free-living marine Enoplida are large-sized nematodes. Of the families investigated, representatives of Leptosomatidae proved the longest with a length of 30 to 50 mm (10 to 20 mm on the average), while nematodes of Anticomidae and Rhabdo- demaniidae are the shortest, not exceeding 7.0 to 8.0 mm (3.0 to 4.0mm on the average). In family Crenopharyngidae forms somewhat longer than those in family Anticomidae predominate, ranging from 5.0 to 6.0 mm in length.
Nematodes are distinguished from many other organisms in that no clear-cut demarcation occurs between the head and the body. The follow- ing sections can be delineated in the body: 1) anterior trophic-sensory section, including oral organs, entire esophagus with chemo- and tangore- ceptors, and the nerve ring, which is the main part of the nervous system; 2) middle trophic-genital section, with midgut and gonads; and 3) caudal section with caudal glands for attachment and such sensory organs as setae and papillae. A.A. Paramanov (1962) has observed that promorpho- logically two types of symmetries are evident in the trophic-sensory section of the body—bilateral symmetry as the base with radial symmetry superimposed. Organs situated in the trophic-genital section promorpho- logically correspond to bilateral symmetry in disposition. In the caudal section radial symmetry of the organs is observed, which should be consid- ered a derivative of the bilateral symmetry. Thus radial structures are typical of the most mobile and active body parts, i.e., trophic-sensory and caudal sections, which serve as the central part of the sensory apparatus.
At first glance it would seem that the shape of the body in all nema- todes is rather uniform. However, a closer scrutiny reveals that shape varies from filiform to pyriform. Variations encountered in free-living and plant nematodes are discussed here. It has been observed that in re- presentatives of lower Enoplida a thin cylindrical and fusiform shape is much more common. A fusiform body is characteristic of nematodes of family Anticomidae; their body considerably tapers at both ends, narrow- ing in the region of the trophic-sensory and caudal sections. The tail in
7
Ke)
8
anticomids is long and consists of two parts—base widely conical and rest extremely narrow and cylindrical.
- In Crenopharyngidae the body shape is similar to that in Anticomidae but longer and tapering in the trophic-sensory section is not so abrupt. In representatives of family Leptosomatidae the body is slender, cylin- drical, and tapers rather smoothly in the trophic-sensory part; the tail is usually short and bluntly rounded. In Rhabdodemaniidae the trophic- sensory end of the body narrows quite smoothly near the cephalic end; the tail is rather long, wide, and pointed at the tip.
As suggested by de Man the shape of the nematode body can be char- acterized by indices expressing ratios of its individual parts. In addition to these indices, measurements have also been given in the form of a formula as suggested by Cobb and modified by Filip’ev (1916).
Cuticle. Represented by a thick membrane covering the nematode body externally and also extending inside the oral aperture, esophagus, hind gut, vagina, and cervical pore. In all probability the cuticle of free- living nematodes plays a dual role—it protects their body from damage and serves as an external skeleton. It plays a particularly important role for nematodes inhabiting sea-breaker zones in which sharp particles of the bottom are moved about. The firmness of the cuticle in different groups of nematodes is ensured in various ways. In nematodes of the orders Chromadoridae and Desmoscolecidae the cuticle is annulated; it is also reinforced with different sclerotized structures such as spherical bodies, bands, denticles, etc., acquiring a great complexity. The cuticle of lower enoplids is relatively simple. In most cases it is absolutely smooth and very thick. In species of Leptosomatum and Leptosomatides extremely fine fasicles of criss-crossed fibers underlie the cuticle and play a support- ing role, imparting great strength to the membrane. These fibers usually occur only in the anterior part of the nematode body.
On the surface of the cuticle longitudinal and lateral structures, term- ed “‘lateral fields,” extend along both sides of the body. These lateral cuti- cular fields generally have their own pattern, which is distinct from the pattern of the cuticle. Along these fields small ridges occur, divided by longitudinal lines. The lateral fields lie against the longitudinal thickening of the hypoderm. Paramonov (1962) suggests that since the lateral field is Situated between two masses of muscles (laterodorsal and lateroven- tral), it may be compared to a lateral cuticular crest, which is formed under the bilateral mechanical influence of these muscular masses. From this idea Paramonov concludes that the genesis of the lateral fields is associated with the locomotor function of the muscles. Thus the support- ing role of the cuticle is revealed in the process of locomotion. This phenomenon (when external skeletal structures play a supporting role for musculature) is quite widespread in the animal world and hence nema-
todes are no exception in this respect.
Histologically the cuticle of enoplids is represented by a noncellular membrane secreted by the hypoderm. It is multilayered. As shown by Timm (1953), the cuticle in Leptosomatum acephalatum consists of six layers: an external homogeneous cortical layer, thin external layer with oblique fibers, thicker layer with fibers running at an angle to the previous layer, two layers similar to each other in structure which stain differently, and the innermost layer or basement membrane consisting of longitudi- nal fibers.
Studies of Thoracostoma coronatum and Deontostoma magnificum re- vealed that their cuticle is similar in structure to that of Leptosomatum acephalatum; hence Timm assumed that in all nematodes of family Lep- tosomatidae the cuticle is similar in structure. The cuticle lining the inner parts of the body consists of a different number of layers, that lining the rectum consists of three layers, while that lining the vulva consists of six and is sclerotized.
The relative thickness of the cuticle is directly related to its structure. The cuticle of enoplids, devoid of supportive structures, is significantly thicker than the annulated and sclerotized cuticle of chromadorids and desmoscolecids, since its strength depends only on its thickness. For ex- ample, in Cyatholaimus and Chromadora (order Chromadorida) the thick- ness of the cuticle constitutes only 1/40 to 1/50 of the body width, while in enoplids the cuticle is much thicker.
Understandably in smaller forms, 2.0 to 5.0 mm long, the cuticle is thinner (2.0 to 5.0 wm) than in larger forms, up to 20 to 30 mm long, in which it may achieve a thickness of 17 to 20 wm. For this reason the absolute thickness of the cuticle should not be taken into consideration and only its relative thickness in comparison to size and thickness of the body examined.! Species of Thoracostoma, Deontosoma, and Pseudo- cella have a cuticle about 1/14 to 1/20 of the body width; Leptosomatum and Leptosomatides—1/15 to 1/18; Synonchus and Cylicolaimus—1/12 to 1/17; and Anticoma—1/14 to 1/20. The thickness of the cuticle reduces only rarely to 1/25 to 1/30 of the body width (as in the case of Anticoma behringiana, Anticoma elegans and Anticoma filipjevi). In Rhabdodema- niidae the thickness of the cuticle constitutes about 1/12 to 1/16 of the body width.
Setae and papillae. These play the role of sensory organs. As out- growths of the cuticle, they are thought to be derived from it. In lower enoplids a great variety in shape, size, and location is seen. Papillae are firmly attached to the body and immovable. Six in number, they are
1Thickness of the cuticle and the corresponding width of the body were measured by me in the region of the nerve ring.
1
=
10
arranged in a circle around the oral aperture immediately behind the lips. In some free-living marine nematodes, labial papillae resemble setae (Filip’ev, 1921). In my material, Leptosomatides acutipapillosus possessed such setaceous papillae. In larger leptosomatids (Thoracostoma, Deonto- stoma, Pseudocella) papillae are well developed and distinctly visible. In Anticomidae labial papillae are arranged as in Leptosomatidae but due to their small size barely discernible. Contrary to females, which have only labial papillae, many males possess a system of preanal papillae (see p. 37).
Setae are the same in origin as the papillae but articulate with the body. All the nematodes of the families described by me have a crown of ten cephalic setae located immediately behind the cephalic capsule; eight are situated in pairs submedially and two single ones situated laterally. If interlobular grooves (p. 37) are present, the cephalic setae are located in them. The shape and size of the cephalic setae vary considerably within the limits of a genus.
In addition to cephalic setae, in many free-living nematodes setae also occur in the preneural region (anterior end of the nematode body from the head to the nerve ring). However, among leptosomatids these setae are absent in a number of species. In Leptosomatum kerguelensis they are rudimentary and transformed into papillae; in L. clavatum these setae are totally absent. It should be noted that in nematodes of Leptosomatum these setae are generally very small and, probably, tending toward reduc- tion. In species of Thoracostoma, Deontostoma, and Pseudocella setae are invariably present but again generally small in size.
The setaceous armature in species of Synonchinae (family Lepto- somatidae) varies notably. Synonchus murmanicus has a few small setae dispersed in the preneural part of the body. Anivanema magna is armed with long and powerful setae situated in regular longitudinal rows. In Eusynonchus hirsutus the entire preneural part is covered with longitu- dinal rows of fine and long setae.
The preneural setae in Anticoma (family Anticomidae) warrant spe- cial attention. Their arrangement in two longitudinal lateral rows, each comprising three to eight setae, seems a characteristic feature of this genus. There are no setae outside these two rows in the preneural region of Anticoma. As shown by Micoletzky (1930) and Wieser (1953b), the number of setae changes with age. Adult Anticoma campbelli (Wieser, 1953c) have four to five setae in each row, while younger forms have only one to two. Hence until the last molt the number of cervical setae in Anticoma cannot be established.
The nature of the cervical setae in Paranticoma, and also in members of the family Anticomidae, is very interesting. These setae merge into a powerful spine inside which lies the duct of the cervical gland.
11
In addition to cephalic and cervical setae, males of many nematodes have a group of preanal setae, functionally entering into the composition of the copulatory organs (p. 37).
Lastly, small setae are present at the tip of the tail near the aperture of the caudal glands.
Head. A study of the head of nematodes of the order Enoplida is very important in the systematics of this group. Complex formations in the anterior end of the body, partly from the external cover (cuticle) and partly from the anterior end of the digestive system, together constitute a single structure in a morphological and functional sense. The degree of development and individual details of structure of these formations are considered the most important taxonomic features of the order Enoplida.
Works by Wieser (1953a) and Inglis (1964) in particular present a comparative anatomical analysis of the anterior body end of enoplids. Due to the fact that some of the propositions by Wieser were subjected to detailed criticism by Inglis, the scheme of the latter author appears better founded and I have utilized his terminology, translating some terms into Russian. The internal layer of the cuticle is significantly thickened at the place where the anterior end of the esophagus comes close to it; this thickening, resembling a cylinder or truncated cone, is called the cephalic capsule (Figure 1, 8). According to Inglis (1964) it consists of an endo- and mesocuticle. The outer covering of the anterior end of the esophagus also has a thickened cuticle. This thickening is labeled the esophageal capsule (Figure 1, 9) (according to Wieser, 1954—pharyngeal Capsule). The junction of the esophageal and cephalic capsules is accentuated by a thickened wall encircling the body, which is called the cephalic ring (Figure 1, 5). Wieser calls this structure the “‘stomodeal ring”. However, the former name appears more appropriate because Inglis showed that nerves innervating the labial sense organs always extend under this ring; for this reason the latter should be associated with the cephalic capsule and not with the esophagus. One more sclerotized structure—the cervical capsule—which is distinguished from the cephalic capsule by striations or punctation, is situated behind the cephalic capsule, often merging with it and extending into it (Figure 1, /0).
In Leptosomatidae and Anticomidae the cephalic capsule extends for- ward beyond the cephalic ring, a feature not seen in representatives of a number of other families of the order. However, its anterior part is always more weakly developed than the posterior part. Sometimes the anterior and posterior parts are so well demarcated that the cephalic capsule seems to consist of two separate elements. Kreis (1928) observed this phenomenon in species Pseudocella saveljevi (under the name Thoraco- stoma conicaudatum) and Pseudocella filipjevi and spoke of primary and secondary capsules (primaer- und sekunderkapsel).
1
N
12
In a number of cases, for example in Thoracostoma, Deontostoma, Pseudocella, and Parabarbonema, the anterior margin of the cephalic cap- sule forms six protuberances supplied with nerves; these extend toward the labial papillae and thus play the role of supporting structures (Figure 1, 11). The posterior part of the cephalic capsule may be divided into six lobes—four sublateral, one dorsal, and one ventral (Figure 1, /2). The lobes are separated from each other by interlobular grooves or furrows resembling arches or narrow fissures, each of which generally has a round anteriorly widened portion—the fenestra (Figure 1, /3). The lateral interlobular grooves, in which the amphids are situated, are much wider than the others. The margins of the lobes of the cephalic capsule may be smooth, or uneven, or wavy with more or less deep marginal grooves. The lobes may or may not exhibit openings or loculi of various shapes.
The oral cavity commences with the mouth and communicates with the esophageal cavity in the simplest cases (Figure 1, 5). With the devel- opment of sclerotized lips and deepening of the oral cavity, the oral open- ing varies in shape, becoming hexagonal or even circular for example. The oral cavity of Leptosomatidae in the original form is almost nil (for example in Leptosomatum). However, in other Leptosomatidae and also in other families of the order, it may change substantially. In species in which the esophagus reaches almost up to the anterior end of the body, as usually happens in Leptosomatidae and Anticomidae, the oral cavity remains undivided. However, in most families of the order the esophagus does not reach the anterior end; consequently two parts of the oral cavity communicate with each other—the onchial cavity, formed by the widen- ing of the anterior esophagus (Figure 1, 7), and the buccal cavity situated in front of the onchial cavity (Figure 1, 3). Differences in the nature of the oral armature correspond to this division. The onchial cavity may exhibit falcate or lamellar processes—the onchia (Figure 1, 6). The onchia move by the action of the musculature of the esophagus, which undergoes specialization at this place and splits into separate muscular fascicles. All the structures of the buccal cavity are not directly connected with the musculature and are brought into motion only through the displacement of three thickened plates formed from the lining of the onchial cavity. The armature of the buccal cavity may be of two types—small denticles situated individually or in groups (odontia), or as in the case of Enoplida plates of thickened cuticle in the cavity (jaws) (Figure 1, 2). The jaws, as shown by Inglis (1964), form through the fusion of the cuticular lining of this cavity with the so-called buccal rods (longitudinal thickenings or ridges formed from the cuticle), and play the role of supporting structures in forms devoid of odontia. Due to the fact that in Leptosomatidae and Anticomidae a distinct division into buccal and onchial cavities does not appear, onchia in representatives of these families may be arranged near
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the oral aperture and never form jaws; the only buccal armature in this case comprises odontia, or plates formed by their fusion. Moreover, odontia may be arranged at the level of the anteriormost onchia. Such an arrangement is in conformity with the circumstance that the esophageal musculature, in the form of anterior specialized muscles, extends far in front and is attached to the bases of the onchia.
In the anterior part of the body of representatives of order Enoplida a number of different cuticular elements are present, such as the cephalic capsule with the cuticle of the body wall covering both sides, cuticular lining of the oral cavity, and the esophageal capsule. These three struc- tures, together with the tissues underlying them, confine externally both dorsally and ventrally a ring-shaped space filled with a liquid and termed the cephalic bladder (Inglis, 1964) (Figure 1, 4). Strictly speaking the cephalic bladder is precisely ring-shaped only in those forms in which the esophageal capsule is situated far away from the anterior end of the body and the oral cavity is narrower than the diameter of the integument around it. Even in sucha case, however, it should be borne in mind that the oral cavity is trigonal and the entire ring appears to be represented by three separate parts corresponding to the sections of the esophagus, divid- ed by narrow crosspieces in those places where the corners of the esopha- geal space come extremely close to the body wall (along the radius of the esophagus). In Leptosomatidae and Anticomidae, however, it often happens that the cephalic bladder is subdivided not into three, but into six parts due to specialized muscles extending toward the onchia and passing along the middle of the esophageal sections, crossing the parts of the cephalic bladder corresponding to each section, and thus dividing it into halves (three sections, each divided into two, for a total of six). The size of the bladder depends on the distance between the anterior body end and the esophagus. In Leptosomatum the esophagus extends almost to the anterior body end and hence there is no cephalic bladder. In Anticoma and genera close to it the cephalic bladder is very poorly developed. In those genera (Parabarbonema, Synonchus, Thoracostoma, and others) in which the esophageal capsule falls short of the anterior end by a signifi- cant distance, the cephalic bladder is well developed.
When the oral cavity is significantly developed, for example in Cylico- laimus and genera close to it, the size of the cephalic bladder shrinks due to an increase in the transverse diameter of the space of the oral cavity.
Thus a detailed study of the cephalic end makes it possible to draw some conclusions regarding the taxonomic structure of lower enoplids. In representatives of Leptosomatidae two lines of development can be traced: first, reinforcement of the cephalic and esophageal capsule and development of the cephalic bladder; and second, development of the oral cavity. Anticomidae is characterized by poor development of the cepha- lic capsule and the oral cavity.
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\ S ES ? P24 3 O77,
et
Figure 1. Scheme of head structure of nematodes of superfamilies Leptosoma- toidea (left) and Enoploidea (right). 1J—oral aperture; 2—odontia (mandibles); 3—buccal cavity; 4—cephalic blad- der; 5—cephalic girdle or ring; 6—onchia; 7—onchial cavity; 8—cephalic capsule; 9—esophageal capsule; /0—cervical capsule; //—anterior protuber- ances of cephalic capsule; /2—lobes of cephalic capsule; 13—interlobular grooves.
Hypoderm. The compact layer of the hypoderm, replacing the epithe- lium, underlies the cuticle which covers the body. The hypoderm has a distinctly cellular structure in free-living marine and a few fresh-water nematodes; it is syncytial in parasitic and most plant nematodes. The nuclei of the cells of the hypoderm disintegrate into a number of smaller nuclei (Martini, 1909). Localized thickenings of the hypoderm press into the pseudocoel and form four longitudinal cords—usually two lateral, one ventral, and one dorsal.
In nematodes of the order Enoplida there are eight hypodermal cords. In addition to the four mentioned above, four submedial cords are pre- sent. The cells of these cords are usually more stretched in width than in length. The hypoderm situated between the cords contains no nuclei. In transverse section the number of cells forming these cords differs in dif- ferent leptosomatids. Thus three cells occur in Synonchus strasseni (Tirk, 1903), five to six cells in Thoracostoma setosum (de Man, 1904), and four
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to five cells in Leptosomatum acephalatum (Timm, 1953). According to the observations of Filip’ev (1916) the greater number of cells in the hypo- derm is related to their increase in other organs also. According to Timm (1953) the dorsal and ventral cords in leptosomatids commence as a double row of large cells at the level of the amphids, while the lateral ones commence as a single row of large cells immediately behind the amphids, but beyond the eyes change into a layer consisting of a large number of cells (there are three rows of cells in the case of Leptosomatum acephalatum). Dorsal and ventral cords are wide anterior to the nerve ring but narrow behind it. Cells in the hypodermal cords are usually arranged in a single row between the eyes and the nerve ring. Beyond the nerve ring these cells reduce greatly in size (especially in the dorsal cord) and hence it is difficult to detect them. Lateral cords widen toward the base of the esophagus, become significantly thickened, and then extend along the entire body. These cords flatten, especially in sexually mature females, in the gonadal region. Throughout their length from the esoph- agus to the anus the lateral cords look like a thin, single, stretched cell, while the ventral cord alternately appears single-celled and double-celled. In the postanal region the ventral cord, wide in transverse section, con- sists of two cells. The dorsal cord disappears altogether but the lateral cords extend right up to the caudal glands and terminate at some distance from their openings.
The cells of different cords vary in form as well as in function (Filip’ev, 1921). Those of the dorsal and ventral cords accumulate fat and hence their shape is usually round, while those of the lateral cords may be rectangular or highly stretched.
Musculature. The nonspecialized musculature of the nematode is represented by a single layer of elongated, fusiform muscle cells under- lying the hypoderm. It is divided into longitudinal muscular fields by the hypodermal cords. According to Schneider (1866) all nematodes can be divided into two groups on the basis of the number of cells in the muscu- lar fields viz., ‘“‘polymyarian” (large number of cellular rows in each mus- cular field with varying number of cells) and ‘‘meromyarian”’ (reduced and fixed small number of cells in each field). All representatives of order Enoplida belong to the first group. According to Timm (1953) in Leptosomatum acephalatum there are six to seven rows of cells in each muscular field in the anterior esophageal region, but commencing from the nerve ring and right up to the terminus the number of cell rows in- creases to ten to twelve.
As already mentioned, the somatic muscle cells of nematodes are fusiform. That part of the cell pressing (bulging) into the pseudocoel consists of only sarcoplasm with a nucleus and without myofibrillae. Myofibrillae are situated in the remaining part either in the shape of a
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longitudinal groove (coelomyarian type) or in the shape of a flat field (platymyarian type). The specialized musculature of nematodes of the family Leptosomatidae was studied in detail by Timm (1953), but mainly in Leptosomatum acephalatum.
The valve of the caudal glands is stretched backward by a thin mus- cle which passes through the middle of these glands. In nematodes of Leptosomatum and Thoracostoma the retractor of the caudal glands has nuclei in its dorsal wall.
Esophageal and intestinal musculature are represented by short mus- cles extending from the body wall to the esophagus and intestine. These muscles are barely separated from each other and lie somewhat above or below the cardia. They support the mesenteric tissue, which at the level of the cardia is rather profuse, and exhibit no fixed pattern in disposition.
De Man (1886) described four median muscles in Enoplus communis of the family Enoplidae, proceeding anteriorly from the base of the esophagus, merging with four sublateral muscles, and binding them with the body near the submedian line. Each muscle consists of a single cell. Tiirk (1903) described similar musculature for Synonchus and Timm (1953) for Leptosomatum.
The structure of the specialized musculature of the head of enoplids was studied in detail by Inglis (1964); hence in analyzing these structures I have used his information extensively.
The musculature of the head is actually the end results of the trans- formation of the anterior end of the esophagus, which developed a series of separate muscles corresponding to the cephalic capsule. All these muscles are attached to the onchial region; the armature of the buccal cavity is completely devoid of musculature. These muscles originate from the external surface of the esophagus. The muscles of the head are represented, so to speak, by two rings situated transversely to the body axis, one of which lies inwardly and somewhat behind the other. Let us tentatively label the first ring posterior and the second anterior. Each ring consists of a few muscles. Moreover, their definite combination repeats itself in each esophageal section. In each section of the esophagus there are three muscles in the anterior ring and four in the posterior one, which are so arranged that the ends of the muscles of the anterior ring pass through the initial parts of the muscles of the posterior ring. In the anterior ring there is a medial unpaired muscle, narrow and thin at the posterior margin but widening and thickening toward the anterior end (Figure 2, /). It is bordered by a pair of muscles which are always signi- ficantly smaller and thinner (Figure 2, 2). In the posterior ring paired medial muscles are also found but they are separated from each other by the initial part of the medial muscle of the anterior ring (Figure 2, 3). Paired lateral muscles (Figure 2, 4) also border the medial muscles of the
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posterior ring. The muscles of the anterior ring extend forward and inward up to their attachment with the onchial plate. The medial paired muscles of the posterior ring are also attached to the onchial plate but situated somewhat lower than the muscles of the anterior ring. The later- al muscles of the posterior ring are attached to the thin cuticle fringing the onchial plate.
The nonspecialized musculature of the esophagus in which the mus- cles are situated radially follows the specialized muscles of the head. This changeover from the two rings of specialized muscles to the radial mus- culature of the esophagus takes place abruptly with no distinct zone of transition. It should be noted that the opening through which the nerve passes to the labial sensory organs occurs between the medial and lateral muscles of the posterior ring.
Figure 2. Cephalic musculature of Enoplidae (only one section shown) (from Inglis, 1964).
7—medial unpaired muscle of anterior ring; 2—paired muscle of anterior ring; 3—medial paired muscle of posterior ring; 4—paired lateral muscle of posterior ring.
A similar arrangement of specialized muscles is mainly characteristic of representatives of family Enoplidae, which were studied by Inglis. I am inclined to assume that a similar scheme of muscular arrangement is also characteristic of lower representatives of the order. The beautiful diagrams of de Man (1904) substantiate this assumption, where in trans- verse sections taken in the cephalic region of Deontostoma antarcticum and Thoracostoma setosum all the muscles described by Inglis (Figure 3)
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can be easily traced. It should be noted that in Anticomidae and the majority of Leptosomatidae the cephalic muscles pass forward through the cephalic bladder, dividing the latter into six small pockets or obliter- ating it altogether.
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Figure 3. Structure of apical end of head of Thoracostoma (section at level of labial papillae—A; cephalic setae—B) (from de Man, 1904).
Specialized musculature of female. A V-shaped muscle extends from the subdorsal body wall to the dorsal part of the rectum, which originates from the posterior part of the rectum. This muscle bears two thin lateral connectives which approach the middle part of the caudal glands and are bound to the dorsal body wall by a third connective. Large nuclei lie in the central part of these connectives. Two small muscles, encircling the lower part of the caudal gland and extending toward the anterior part of the rectum, originate from the subdorsal body wall. These muscles raise the dorsal body wall during defecation.
Ten to twelve pairs of muscles, extending from the ventrolateral body wall toward the vagina and vulva, originate from the anterior and poste- rior parts of the vulva. The lateralmost pair bind the uterus and the vagina, while the centralmost pair bind the lips of the vulva. There is one nucleus in each of these muscles. All the nuclei are situated at one level, i.e., near the place of origin of the vulval muscles from the body wall. The number of pairs of these muscles probably varies in different species. Thus in Leptosomatum acephalatum there are 10 to 12 such muscles, while in Thoracostoma coronatum there are 6 to 8.
Five to six pairs of muscles, extending from the dorsolateral wall to the dorsal side of the vagina, are situated in the region of the vulva. They widen the vagina at the time eggs pass into it from the uterus. Two thick
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muscles, each with one large nucleus, lie anterior and posterior to the vagina. These close the vulval opening. Two muscle cells lie dorsal to the vulva. Probably, they also assist in closing the vulval opening. In Thoracostomum coronatum there are two very large muscles on each side of the vagina which keep it closed.
The sphincter of the uterus is a highly reduced muscle situated near the uterine neck just ahead of the vagina. The muscular layer which on widening forms the sphincter extends further in the shape of a thin mus- cular investment around the vagina.
Specialized musculature of male. The V-shaped anal muscle of the male extends from the subdorsal wall of the body toward the posterior anal lip. The nucleus of this muscle lies near the body wall.
The copulatory musculature of the male is represented by numerous, thin, paired muscles (about 40 pairs), extending from the ventral side of
- the lateral walls to the subventral side of the body and terminating in the anterior part of the anus. Two to three pairs of short muscles extend from the ventrolateral wall of the body to the anterior lip of the anus; their function is to lift the anal lip. Tiirk (1903) described the copula- tory muscles situated behind the anus in the case of Synonchus. Timm (1953) could not find similar muscles in Leptosomatum acephalatum.
The retractor musculature of the spicules is represented by paired muscles originating dorsal to the body wall, extending toward the lateral wall, and reaching the capituli of the spicules.
The protractor musculature of the spicules also consists of paired muscles. They form a longitudinal layer on the dorsal surface of the spicular pouch. Their nuclei are elongated.
The retractor musculature of the gubernaculum likewise consists of paired muscles which extend from the dorsal wall of the body and pass by the proximal end of the gubernaculum. In males the intestino-somatic musculature commences immediately after the esophagus, and consists of a thick muscular projection which surrounds the intestine but does not adhere to it. This projection is actually a series of irregular blocks of muscular tissues, which are attached to the somatic muscular layer or the body wall. Nuclei are usually found in the sarcoplasm of the muscular layer but may also be situated between the muscular projection (case) and the somatic layer. The testes and vas deferens may also be partially surrounded by the muscular case in the posterior part of the body. The muscular case then consolidates in large muscular blocks which are at- tached to the testes beyond their distal end.
Glands. These are always unicellular. In leptosomatids glands of the lateral fields look like large cells with a dark granular content. They are connected to the body wall by slender ducts. Near the outlet of these
18 ducts a seta is often present. Bastian (1865) was the first to discover these
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glands. Subsequently they were described by de Man (1893) in Thoracos- toma coronatum; by Marion (1870) in Thoracostoma zolae; by Jagerskidld (1901) in Cylicolaimus magnus and Jaegerskioeldia acuticaudata; by Turk (1903) in Synonchus, Tuerkiana, and Paratuerkiana; by de Man (1904) in Thoracostoma setosum and Deontostoma antarcticum; and by Steiner (1916) in Leptosomatides steineri.
Marion thought these glands served an adhesive function, secreting a substance whereby the nematode attaches itself to the substratum. Jagerskiéld assigned an excretory function to these glands. Zur Strassen (1904) considered them supporting cells of the nerve endings. Filip’ev (1921) deemed their nature glandular; surprisingly he reports these glands mostly for leptosomatids, whereas earlier authors mention them only for certain species in other groups of nematodes.
The cervical gland or renette is represented by a large unicellular structure in the anterior part of the nematode body (Figure 4). This gland is filled with a white secretion and stains darkly with hematoxylin. Two types of cervical glands are distinguishable: pyriform, with thick body, and short and slender duct; and tubular, with long stretched body, and long, thick duct. The renette body commences usually in the anterior part of the intestine or slightly above it, i.e., at the base of the esophagus. Usually this gland lies along the ventral line but sometimes it bends toward the dorsal side. In Anticoma (family Anticomidae) this gland is much larger and hence readily detected. It usually commences from the
/| —oIEW
Figure 4, Anterior end of Anticoma (R—renette).
74)
base of the esophagus and may open either in the pre- or postneural region. The position of the opening serves as a diagnostic character for species identification (pp. 148-174). Sometimes the glandular pore is highly displaced toward the anterior end and may open at the level of the amphids.
In species of Leptosomatidae the presence of the renette has proved controversial. According to Jagerskidld (1901), Turk (1903), Steiner (1916), and Timm (1953) even the most thorough examination did not reveal the presence of this gland in Synonchus, Tuerkiana, Paratuerkiana, Cylicolaimus, Thoracostoma, nor in Leptosomatum acephalatum and Lep- tosomatides steineri. Filip’ev (1916) described the cervical pore in Deon- tostoma papillatum and de Man (1893) in Thoracostoma coronatum; the cervical gland per se they declared absent. Filip’ev (1921) expressed the possibility that the gland disappears during the cycle of development of the nematode.
The nature of the function of this gland was resolved after a long debate. Golovin (1902), Rauther (1907, 1909), and Stefansky (1922) in- vestigated this problem experimentally by staining nematodes with vital stains. They arrived at the same conclusion—that the renette serves as an organ of excretion and osmoregulation. Stefansky (1922) and Para- monov (1962) positively attribute these functions to the renette but do not consider it the only organ of excretion. The excretory function is carried out by the renette, caudal glands, esophagus, and intestine.
In nematodes of the subclass Adenophorea the renette is compact and massive; a dendroid and very complex structure is characteristic of the renette in all members of the subclass Secernentea.
As indicated by Paramonov (1962), with a reduction in the protone- phridial system in the ancestors of nematodes, a need for its replacement arose. In the earlier nematode stages of phylogenesis the excretory system was probably very bulky and consisted of a number of dermal glands. Afterwards, during the process of oligomerization three caudal and one cervical gland formed.
It seems to me that the absence of a renette in species of Leptosoma- tidae points to the fact that the process of its formation is still in the initial stages. In those forms in which this gland is absent its function is probably carried out by the glands of the lateral fields, caudal glands, the esophagus, and the intestine. The presence of glands in the lateral fields in leptosomatids (Filip’ev, 1921) also seems to support this idea. The fact that the renette also happens to be an organ of osmoregulation is sub- stantiated by its absence in typical marine leptosomatids in which there is little need for such. Representatives of Anticomidae, largely found in pure fresh-water bodies, require a special organ of osmoregulation and the renette is quite well developed in anticomids. Its presence also bespeaks
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the higher organization of Anticomidae.
There are three caudal glands, one on the dorsal side and two on the ventral.
Leidig (1854), followed by Eberth (1863), described these glands in the caudal region of nematodes. These scientists introduced the term ‘caudal gland’’. In structure these glands are reminiscent of the cervical gland and stain deeply with hematoxylin (Jagerskidld, 1901). Like the cervical, two types of caudal glands are also distinguishable—tubular and pyriform. In lower enoplids both types are found (Figure 5), while various types may be seen in closely related forms. Hence this character lacks taxonomic significance. As can be seen from Figure 5, between the two aforementioned types of glands intermediate forms occur. All three caudal glands open at the extremity of the tail through a common caudal pore situated, most often, terminally. Occasionally this pore is somewhat displaced toward the ventral side. The caudal cone, sometimes longitudi-
y
Figure 5. Shapes of caudal glands in lower Enoplida. 1—Leptosomatum; 2 to 4—Synonchus; 5—Rhabdodemania; 6—Leptosomatides.
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nally striated (Figure 5, 7 and 2), usually lies in this pore. Cuticular folds usually develop around the caudal cone and provide support. The sub- stance secreted by the caudal glands becomes firm on contact with water and hence these glands have been labeled ‘‘adhesive glands’’.
Body cavity. Primary form of body cavity—schizocoel devoid of epi- thelial lining and formed asa result of dispersion and disintegration of mesodermal cells. In more primitive nematodes it is usually difficult to observe the schizocoel as it is filled with nerve, muscle, and phagocytic cells. This led to the denial of its existence by Jagerskidld (1901) in Cy/i- colaimus and Jaegerskioeldia, by Tirk (1903) in leptosomatids of the Mediterranean Sea, and by Timm (1953) in species of Leptosomatum, since none of these authors could detect a schizocoel in their material. De Man (1904) discovered only narrow slits in Thoracostoma setosum.
In intestinal and saprozoic nematodes living in an anisotonic medium the body cavity is represented by larger spaces containing liquid. In the changeover of nematodes to tissue parasitism in an isotonic medium the body cavity disappears and is filled with inflated cells which are paren- chymatous in character (Filip’ev, 1937).
Phagocytic cells are located inside the body cavity. They are spherical and filled with a lustrous granular content. They have been studied in great detail by Golovin (1901). In nematodes placed in vital stains these cells stain quite rapidly. Other cells lose their stain on storage while phagocytic cells retain their stain for a long period; furthermore the stain sometimes crystallizes in their cytoplasm. These cell have an acidic reaction. Golovin directly proved their phagocytic nature; in transected worms they ingested India ink directly from sea water. Shimkevich (1899) was the first to record their phagocytic nature.
Phagocytic cells are scattered in large number throughout the length of the nematode body. According to Filip’ev (1921), the number ranges from 100 to 220 in nematodes of the order Enoplida. In some nematodes their disposition is irregular, while in others they are arranged mainly along the veniral line. Such a type of arrangement is characteristic of species of Leptosomatum and Leptosomatides.
These cells are more systematically disposed in more highly organized families of free-living nematodes such as Cyatholaimidae, Chromado- ridae, and Axonolaimidae but their number markedly reduced. In Axo- nolaimus setosus, for example, there are only two large phagocytic cells (Filip’ev, 1918, 1921). They are comparable to the large phagocytic cells of parasitic nematodes.
Lipid cells are also present in the body cavity of nematodes. True, they have not been studied much and information about them is very scanty. Tiirk discovered such cells in Synonchus strasseni. They are dend- ritic in shape and situated around the intestine. Rauther (1907) observed
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them in Cylicolaimus and Thoracostoma. Shimkevich (1899) and Golovin (1901) considered them homologues of phagocytic cells.
The observations of Timm (1953) in his more recent works should be noted. He has described similar cells in Leptosomatum acephalatum. In the female a paired row of such cells lies freely in the body cavity along the uterine region. A large number are disposed around the oviduct. The nucleus of these cells is located in the center of the cellular body. Some of these cells are bifurcated (bifid) at one end. They are supported by the mesenteric connectives which link them with the body wall.
In Enoplus these cells branch and form a network on the intestine. They do not branch in Deontostoma magnificum.
Nervous system. The nervous system of nematodes parasitic in animals has been studied in detail, that of phytonematodes less so, and that of free-living nematodes almost not at all. Details of the nervous system of Paroncholaimus zernovi (family Oncholaimidae, order Enoplida) have been given by Filip’ev (1912, 1921), providing a basis for assuming that within the limits of the order Enoplida the general structural plan of the nervous system is similar. The scheme proposed by Filip’ev has been followed here. The nervous system of nematodes represents an extremely low level of organization. It is usually located in the hypoderm and only motor nerves and some part of the central nervous system distinguishable. The nerve ring or so-called circumesophageal ring constitutes its core and encircles the esophagus in its anterior half. In various species of Enoplida this ring occupies a different position in this part of the eso- phagus. Fibers and a small number of nerve cells enter into the compo- sition of the nerve ring; Filip’ev (1912) has distinguished three types on the basis of their composition:
1. Total absence of any semblance of ganglia; nerve cells arranged in a single layer around the esophagus.
2. Barely discernible ganglia (which, as a matter of fact, are only groups of cells).
3. Readily distinguishable ganglia, densely fused with special ‘‘accom- panying”’ and “‘supporting”’ cells.
Only the first type is seen in Enoplida—total absence of ganglia and presence of just a single layer of nerve cells around the esophagus. Nerve cords in the body of nematodes of the order Enoplida are situated as follows (Figure 6): The major and most powerful nerve—the ventral nerve, a pair of subventral nerves, a pair of subdorsal nerves, and a dor- sal nerve located in the postneural part of the body. Two nerves occur on each side in the region of the lateral fields; Filip’ev labeled them the upper and lower lateral nerves. The ventral nerve splits into superficial inner fibers. The latter extend from the hypoderm and not reaching the level of the nerve ring join it in two nerve roots; the superficial nerve fibers
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extend into the hypoderm right up to the level of the nerve ring and, here, like the inner fibers join the nerve ring in two nerve roots in the plane perpendicular to the body surface. Ultimately a small part of the super- ficial fibers extends further, into the preneural section. The subventral nerves merge with the roots of the inner fibers of the ventral nerve at the place of its junction with the nerve ring. Somewhat behind the ventral nerve the upper lateral nerves divide into two groups of nerve fibers, one extending into the preneural part and the other forming the nerve root joining the nerve ring. Subdorsal nerves take a sharp turn and from the hypoderm where they are located run deep and merge with the roots of the upper lateral nerves. The lower lateral and dorsal nerves do not com- municate with the nerve ring and extend past it into the anterior part of the body. Thus six nerve cords of the postneural part extend into the preneural part—the dorsal, two dorsolateral, two ventrolateral, and the ventral. Two pairs of submedial and one pair of lateral nerves are situat- ed deeper than these trunks, near the esophagus, and originate from the nerve cells situated anterior end posterior to the nerve ring. The subme- dial nerves exclusively innervate organs of the anterior body end. The lateral nerves branch into peripheral offshoots which form a compact system that innervates the amphids and various setae. Nerves running from the posterior body end and reaching the peripheral surface likewise innervate different setae.
Figure 6. Schematic diagram of the nervous system of nematodes of order Enoplida.
Nerves: /—dorsal; 2—subdorsal; 3—dorsolateral; ¢4—ventrolateral; 5—subventral; 6—ventral.
Innervation of the organs of the posterior section of the body of free- living nematodes has not been well studied. One can only state that the copulatory organs, bursat musculature of the male, and the vulval region of the female are innervated by offshoots of the ventral and sub- medial nerves.
Organs of sense. Tangoreceptors. In all nematodes these organs are concentrated mainly in the cephalic region; however, in males they also
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occur in the caudal section of the body. Cephalic setae, anal setae, and papillae supplied with nerves serve as tangoreceptors. As these have been discussed above, further comment is not necessary here. Chemoreceptors: These are the lateral organs or amphids and consti- tute organs of chemical sensitivity. These are three main types of amphids in nematodes—cyathiform, circular, and spiral. Their structure is a most stable feature and usually characteristic of a large taxonomic group. Cyathiform amphids, causing a depression in the cuticle, are characteris- tic of the entire orser Enoplida. A papilla with a nerve end intrudes into the closed posterior part. The anterior part of the amphid opens exte- riorly. Amphid size in lower enoplids varies greatly; the width may range from 1/2 to 1/8 of the corresponding body diameter. Form is also vari- able, from circular to cyathiform to oval or elongated in both transverse and longitudinal directions (Figure 7). Location likewise is not constant; amphids may be situated immediately behind the cephalic capsule as in the case of leptosomatids (Leptosomatum, Leptosomatides), in the lateral interlobular grooves (Synonchus, Thoracostoma, Deontostoma, Pseudo- cella), or at some distance from the cephalic capsule; usually, however, this distance does not exceed two to three times the diameter of the head. In anticomids the amphids are arranged somewhat below the level of the cephalic setae and their size varies greatly in different species. It is inter- esting to note that in genus Rhabdodemania amphids are generally absent.
0 0 0 0 i) 0 Q 0 1 2 3 4 5 6 7 8 Figure 7. Shapes of amphids in nematodes of families Leptosomatidae and Anticomidae.
1—Anticoma; 2 to 4—Pseudocella; 5 to 7—Leptosomatum; 8—Platicomopsis (o—opening of amphid).
The functions of amphids have long been debated and range from glandular (de Man, 1886) to auricular (Marion, 1870; Biitschli, 1873). Zur Strassen (1904) put forward the proposition that amphids are organs of chemical sensitivity, i.e., chemoreceptors. This point of view is the
23 most widely held today. However, the problem of the function of am- phids as chemoreceptors cannot be considered conclusively resolved as experimental data supporting this supposition are still inadequate.
Inglis (1964), proceeding from the fact that the function of amphids as chemoreceptors has not been confirmed experimentally, is inclined to attribute to them an altogether different function, namely, receptors of
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mechanical tension of the cuticle. Inglis’ idea is extremely interesting, but unfortunately lacks experimental supportive confirmation.
Photoreceptors. Unlike the amphids, the shape of which is characteris- tic of a definite taxonomic group, photosensitive structures appear con- vergently in different groups of free-living nematodes. The presence or absence of these structures and their shape are features used in species diagnosis. |
Photosensitive organs are always situated in the preneural region of nematodes. Of all the groups of nematodes studied in the present work, they were found only in leptosomatids (Leptosomatum, Leptosomatides, Thoracostoma, Deontostoma, and Pseudocella); their structure is quite complex (Figure 8) except in the last two genera. Each organ consists of dark red or brown pigment in a compact structure, which is circular or cyathiform with the lens situated anteriorly. Such ‘‘eyes” occur along the sides of the esophagus and their lenses project somewhat sideways. They are usually situated at the same level but in some cases (for example in Leptosomatides euxina) one may be situated much above the other. Some-
Figure 8. Structure of photosensitive organ in nematodes of genus Thoracostoma.
1—light-refractive lens; 2—pigment bowl.
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times the pigment projects beyond the limits of the pigment bowl and forms a small dendroid overflow behind it.
In Thoracostoma and Pseudocella a tendency toward reduction of the photosensitive organs is observed. In Thoracostoma most species have ‘“‘eyes’’ exhibiting the structure described above, but a number, for exam- ple T. schizoepistilium, T. philippinensis, T. anocellatum, T. parasetosum, and T. brunni are completely devoid of photosensitive organs. In T. seto- sum only the pigment bowl is present; the lens is absent.
In species of Pseudocella ‘‘eyes’’ with lenses are seldom found. Usual- ly the photosensitive pigment occurs not in a compact mass, but in small spots of irregular shape and light red in color. Sometimes the pigment is dispersed in longitudinal strips with a series of lateral offshoots. Some representatives of this genus are absolutely devoid of pigment; in my material no pigment was discernible in Pseudocella bursata, P. mamilli- fera, P. acuta, and P. angusticeps.
It seems to me that in Thoracostoma and Pseudocella a process of gradual reduction of photosensitive structures is taking place but no loss in their occurrence. The reason for this is that these two genera are more highly organized in all the remaining details of their structure than in species of the genus Deontostoma and still more than in those of Lepto- somatum.
Digestive system. The digestive system of nematodes commences with an oral opening which in some leads into an oral cavity. The latter is extremely varied in structure in lower enoplids as noted above. Here I shall only mention that there are species within the limits of the group of lower enoplids which are absolutely devoid of an oral cavity as well as species with a well-developed and armed oral cavity.
Wieser (1953b) divided all free-living marine nematodes into four groups on the basis of the structure of their oral cavity. Among lower enoplids, three of these four groups are found. Nematodes lacking a distinct buccal capsule belong to the first group. Capturing food in such a case is effected by sucking with the help of the esophageal muscles. Anticoma, Paranticoma, Anticomopsis, Crenopharynx, Antopus, Barbo- nema, Leptosomatum, Leptosomatides, Leptosomella, Platycoma, Plati- comopsis, and Triodontolaimus should be included in this group.
Nematodes with a small oral cavity armed with small teeth or plates to scrape aquatic plants, algae, etc., or bacterial film on various under- water objects, belong to the second group. Representatives of Synonchy- nae and Thoracostominae (Leptosomatidae) belong to this group.
Finally, nematodes with an extremely large oral cavity with a thick sclerotized lining and powerful onchia which can pierce the membrane of aquatic plants and suck the contents of their cells belong to the third group. Furthermore, there are possibly predators which swallow small
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organisms. Lower enoplids differ sharply with respect to type of food ingested and mode of feeding, which is reflected in the variation of struc- ture of the oral apparatus.
The esophagus, which is comparatively uniform in shape in lower enoplids, follows immediately after the oral capsule. Usually the esopha- gus is Straight and widens gradually toward the base. The esophagus of lower enoplids never exhibits true or pseudo bulbs. In transverse section the esophagus exhibits a triradial lumen lined internally with a cuticle with angles intruding inward and musculature arranged in the shape of three longitudinal bands, forming three sections in the esophagus (one dorsal and two subventral). Esophageal glands are situated (see below) in the middle of each section.
The musculature of the esophagus has been studied fairly well in parasitic nematodes (Looss, 1896; Schneider, 1902; Goldschmidt, 1904; Martini, 1916) and in free-living nematodes (Rauther, 1907; Filip’ev, 1921). It has been established that the esophagus in both groups is simi- lar in structure. The tissue is composed of muscular, epithelial, nerve, and glandular cells. Muscular and epithelial cells are so closely arranged that their cellular boundaries are distinguished with great difficulty. The former contain radial muscular fibrillae, one end of which is attached to the internal angles of the esophageal tube and the other to the superficial layer of the esophagus. In lower enoplids muscular bands extend conti- nuously throughout the esophagus. In those nematodes in which the esophagus has bulbs the epithelial tissue may be interrupted by the mus- cular tissue, forming a membrane in the region of the latter and thus imparting to the esophagus great firmness. Several epidermal cells, also containing fibrillae, extend from the anterior angles of the esophageal tube to its surface and are situated along the angles. As distinguished from those described above, these are not contractile but elastic fibers. Derivatives of the epidermal cells represent the external firm membrane of the esophagus. Thus the muscular cells are surrounded, so to speak, by epithelial ones. It should be noted that the number of muscular and epithelial cells of the esophagus is greater in free-living nematodes than in parasitic ones. Thus in Ascaris there are 24 and in Synonchus 42. Moreover, the number in each species is constant (Filip’ev, 1921).
Rauther (1907) suggested that besides its basic function, the esopha- gus also fulfills an excretory one. In his experiments different vital stains accumulated and were then excreted in the angular bands of the esopha- gus. In his opinion the pigment strips sometimes observed in the eso- phagus are actually an accumulation of excrement in the esophageal lumen which is subsequently excreted. The lumen of the esophagus is lined with a cuticle that differs sharply from the external cuticle covering the body. Sometimes bulges are observed in the esophageal cuticle of
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lower enoplids which resemble a stripe in longitudinal sections (Filip’ev, 1921). At the posterior end of the esophagus, where it joins the intestine, a special structure can be isolated which is known as the cardia. In the anterior part of the intestine the cardia projects in the shape of a triangle. Functionally, it serves as a valve, obstructing the movement of food from the intestine back to the esophagus. According to Filip’ev (1921) the cardia consists of clearly distinguishable cells devoid of musculature. Here Filip’ev differs in opinion from Tirk (1903) who discovered a large number of nuclei and annulated muscular fibrillae in the cardia of Synon- chus. Steiner (1915) noted the presence of sclerotized reinforcement in the cardia of Leptosomatum sabangense.
Timm (1953) in studying the cardia in sections from Leptosomatum acephalatum noted that it consists of esophageal tissue surrounded by a thin annular sphincter. which, in turn, is surrounded by the nerve cells of the intestine.
The intestine of lower enoplids, like that of all.free-living nematodes, is represented by a straight simple tube devoid of all outgrowths and blind pouches such as seen in parasitic nematodes. The intestinal wall consists of a single layer of cells. The number of intestinal cells varies considerably in different groups of nematodes. Thus in nematodes of Leptosomatidae and Oncholaimidae the number of cells is significantly more than in Monhysteridae and Chromadoridae (Biitschli, 1873; de Man, 1888; Cobb, 1893a).
According to Timm (1953) the number of intestinal cells in free-living nematodes varies from 123 to 5,000 and two types are distinguishable: unspecialized isocytes and specialized heterocytes. Isocytes are represent- ed by rectangular cells of equal height. Heterocytes are oval cells, the size of which exceeds that of the isocytes by two to three times. As dis- tinguished from the isocytes, these cells have a rough basophilic reticular net. Timm did not observe them in all leptosomatids. He found them in Leptosomatum acephalatum but not in Deontostoma magnificum and Tho- racostoma coronatum. Tirk (1903) observed them in Synonchus strasseni.
In addition to the foregoing cells, a rod-shaped layer (‘‘rood border”’ according to Hyman, 1951; “‘bacillary layer’ according to Timm, 1953) also occurs in the intestinal wall, in which rod-shaped basophilic elements can be distinguished. These structures have been described in detail by Timm (1953) for Leptosomatum acephalatum; Rauther (1907) did not find them in Cylicolaimus.
Inside the intestinal tube lies a smooth radially striated cuticle, and outside it a basal membrane formed partially from the intestinal cells and partially from the connective tissue (Martini, 1916).
In the middle part of the body in sexually mature individuals the intestine may be compressed by the gonads.
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Timm (1953) noted that the intestine of males and females can be distinguished by cellular composition. For example, in Leptosomatum acephalatum he found that the intestine of males consisted not only of a smaller number of cells, but also fewer oval cells, and that the cells were flatter, almost cubical, and very much larger than in females.
The rectum (or hind gut) in females passes through the intestino-rectal valve surrounded by epithelial tissue. The entire rectum is lined with the _ outer cuticle, turned inside, which may extend even farther, i.e., into the intestine. Timm (1953) observed that in sections taken from the part somewhat anterior to the rectum in Leptosomatum acephalatum there were numerous digitiform structures directed into the lumen of the intestine. Probably numerous folds of the cuticle (digitiform in shape) occur here. The rectum is encircled by a thin muscular sphincter. In males the rectum and sperm duct fuse not far from the anus.
Glands participating in the process of digestion are closely associat- ed with the digestive tract. According to Tiirk (1903) and Rauther (1907) the anterior part of these glands is represented by a simple tube, while the posterior part is dendroid. The dorsal gland differs somewhat from the subventral glands. Thus in Cylicolaimus and Synonchus the unbranched part of the dorsal gland runs farther backward than that in the subventral ones. Esophageal glands open either directly into the oral cavity or, in the case of its absence, into the esophagus somewhat posterior to the cephalic capsule. The position of the external openings of these glands varies in different species of nematodes. In nematodes of family Lepto- somatidae the openings of the subventral glands are shifted more toward the anterior end and the dorsal gland is somewhat posterior in position. The duct of the subdorsal gland in Leptosomatum acephalatum opens immediately behind the oral cavity. In Thoracostoma coronatum this duct opens on a small denticle situated in the oral cavity. When two subdorsal glands are present, their ducts open at the same level but not on the same denticle. In Deontostoma magnificum the outlet of the dorsal gland opens on the dorsal denticle and the ducts of the subventral glands open some- what anteriorly (Timm, 1953). Rauther (1907) discovered accessory ‘lateral’ ducts of the glands at the level of the eyes in a Thoracostoma sp. Timm found such ducts in Deontostoma magnificum.
Reproductive system. The female reproductive system of nematodes is represented by a continuous tube, different sections of which serve re- spectively as the ovary, oviduct, uterus, and vagina (Figure 9). In lower enoplids these tubes comprise a pair, one anteriad and the other poste- riad. The anterior and posterior position of the reproductive tubes is a secondary phenomenon. Originally these tubes were situated bilaterally. That they are situated on the right and left side of the intestines bespeaks this fact. Subsequently one tube reflexed and the other remained in its
32
original position. This occurred due to the intense stretching of the body in length and narrowing of the diameter (Filip’ev, 1921; Steiner, 1922b; Hyman, 1951; Paramonov, 1962).
In free-living nematodes the reproductive tubes are always positioned as described above. A bilateral arrangement of the reproductive tubes can
be observed only in some parasitic (Ascaris) and phytonematodes (rep- resentatives of family Heteroderidae).
eceucdddeasae
Figure 9. Structure of female reproductive system of nematodes.
1—reproductive tube of Thoracostoma; 2—anterior reproductive tube of Pseudocella (one large egg E visible in figure).
2
~
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The terminal part of the ovaries of lower enoplids is always reflexed. The reflexed part is significant in length, usually not less than half the length of the straight part, but sometimes equal to it in length, i.e., the ends of the gonads reach the vagina (Anticoma).
The ends of the gonads from which the oogonia separate are syncytial in nature. The oogonia occur first in a cluster and then form a single row. Externally the ovary is covered by a thin epithelium consisting of flat and stretched cells (Cobb, 1893; de Man, 1886).
The ovaries are somewhat displaced toward the dorsal side and attached to the muscular layer near the distal end of the uterus.
The cells of the ovarian epithelium may differ significantly in shape and size in different species of lower enoplids. Thus in Thoracostoma coro- natum a large flat epithelial cell extends the length of the ovary. In Lepto- somatum acephalatum extremely small cells are situated along the short germinal zone, but cells of pyramid shape are situated in the zone of growth; these are significantly larger than the cells of the germinal zone. Before the bend of the ovary the cells become very large and oval. As the genital tracts of nematodes are represented by a single continuous tube, demarcating the ovary and the oviduct becomes somewhat difficult. de Man (1886) distinguished these sections on the basis of their histology. In such a case the ovary is very long and the oviduct represented by a short area continuous with the uterus. Jagerskidld (1901) and Filip’ev (1921) distinguished these two sections on the basis of their morphology, considering the ovary the entire part between the uterus and the depres- sion in the contracted part of the blind sac. The oviduct is represented by that part of the reproductive tube which is separated due to the fact that the former does not join the end of the ovary itself, but a little poste- riorly. Mature eggs are stored in this sac.
In sexually mature females the oviduct exhibits disintegrating spongy tissue throughout its length all along the surface of the ventral body wall between the intestine and the ovary. In such a condition the passage is almost invisible. In younger specimens the wall of the ovary has not disintegrated and the passage is distinctly visible. Timm (1953) observed such a phenomenon in Leptosomatum acephalatum but gave no expla- nation. In this same species he notes the absence of any trace of a spermatheca isolated from the reproductive canal. Spermatozoa were present in the uterus in the region of egg formation in the ovary. In many species spermatozoa often concentrate in the anterior part of the ovary, immediately behind the zone of egg formation. This region probably plays the role of the spermatheca.
Between the oviduct and uterus lies the zone of egg formation in which extremely large cells occur, filling the lumen of the reproductive canal. These cells surround the eggs within the limits of the egg-forming zone
34.
or closely adhere to the eggs entering the uterus. The eggs either pass across the center of these cells or along one side. While entering this zone the eggs are devoid of a shell, but on exiting covered with a firm shell. Timm (1953) considers the function of these large active cells to be shell formation. They probably secrete an enzyme which activates the eggs to form a shell.
The uterus is represented by a relatively wider tube in which the walls consist of flat epithelial cells. Muscular fibers run only along its proxi- mal end. Near the vagina the uterus has a reduced sphincter of thick muscular cells which is located on the ventral side. Unlike a large number of free-living nematodes (Chromadoridae and some Oncholaimidae) which have an unpaired uterus merging near the vagina, in lower enoplids the vagina is always paired and the passages of the two uteri separate.
The number and size of eggs vary considerably even within the limits of a single species. In the uterus of females of different species I have counted from one to nine eggs. The smallest eggs, 50 to 60 um long, I found in Anticoma and the largest, 1,200 wm long, in Pseudocella bursata. Egg size, as mentioned above, varies within the limits of one and the same species. Thus in Leptosomatum tetrophtalmum eggs ranged from 154 to 206 wm in length, in L. kerguelensis—103 to 236 um, in Leptosomatides crassus—154 to 360 um, in L. acutipapillosum—154 to 257 ym, and in Pseudocella trichodes—206 to 412 um.
The female genital pore (vulva) is situated on the ventral side, most often midbody. Sometimes it is shifted posteriorly and very rarely ante- riorly. In females of some nematodes sclerotized granules encircle the vulval slit. Filip’ev (1922a) found this peculiarity in Leptosomatides steineri. I found it in other species—Platycomopsis mesjatzevi and Deon- tostoma arcticum. These granules are frequently found in species of genera Leptosomatum and Leptosomatides. In my material granules sur- rounding the vulval aperture occurred in four species of genus Lepto- somatum and two species of Leptosomatides. ,
It is interesting to note that in females of Paracylicolaimus brevisetosus I detected two vulval slits (Platonova, 1970). This phenomenon is an abnormality. A similar case has been described by Paramonov (1926).
The male genital tubes of lower enoplids are represented by paired testes which pass into two seminal vesicles and merge into a single vas deferens. The latter transforms into an unpaired muscular ejaculatory duct opening into the cloaca. The copulatory organ also opens into the cloaca.
As in the case of female gonads, in males also one testis is anteriad and the other posteriad (Figure 10). The beginning of the testis is rep- resented by a syncytium, giving rise to spermatogonia. Mature sperma- tozoa collect in the posterior end of the testis or in the seminal vesicle.
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The testis is covered externally by a thin epithelium composed of long- itudinally stretched fusiform cells (de Man, 1886) or by an extremely thin and flat epithelium (Jagerskidld, 1901).
The anterior part of the vas deferens consists of numerous low cells with indistinct cellular outlines. The number of cells decreases toward the posterior part of the vas deferens and their outlines become more distinct. The ejaculatory duct, situated next, consists of two rows of cells compressed longitudinally. There is almost no musculature in the ante-
29 rior part of the duct but well-developed musculature present in the poste- rior part (Jagerskidid, 1901; Turk 1903; Filip’ev, 1916).
Figure 10. Diagrammatic sketch of reproductive tube in male.
The copulatory system of males is situated in a special sac of the cloaca and consists of a pair of spicules and a gubernaculum (Figure 11). The spicules are hollow sclerotized organs which curve variously. A plasmatic substance, part of those epidermal cells which form the spicules, develops inside them (Filip’ev, 1921). One can demarcate the capitulum of each
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spicule at the proximal end from the constriction (cervix) following it. The body of the spicule has a lumen in the middle and a thin membrane in the ventral curvature, i.e., the velum. Sclerotized structures directing the movements of the spicules have been labeled ‘‘ruleks’’. This term was introduced in Soviet literature by Filip’ev to replace ‘‘gubernaculum”’, proposed by Looss. The gubernaculum may be paired or single. Mostly it is situated on the dorsal side of the spicules but sometimes ventrally (Platycomopsis mesjatzevi). Sometimes the gubernaculum is altogether absent (Platycoma cephalata, Anticoma longisetosa, A. graciliceps, A. filipjevi, A. uschakovi, A. behringiana, A. brevisetosa, and Paranticoma antarctica).
Filip’ev (1921, 1927) established some types of spicule structures
Figure 11. Diagrammatic structure of spicular apparatus of nematodes of genus Pseudocella.
1—capitulum of spicule; 2—body of spicule; 3—velum; 4—ventral process of gubernaculum; 5—dorsal process of gubernaculum; 6—gubernaculum.
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3
—
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(straight, arcuate, broad, lamelliform, flat, elongated, and complex), under which he formed subgroups. Of the seven main types, three are characteristic of lower enoplids: 1) arcuate (curved spicules which almost do not broaden in the middle; well-developed and complex gubernaculum always present); 2) broad (distinguished from the preceding type by flatter shape and presence of velum); and 3) lamelliform (with velum on ventral side). Broad spicules are characteristic of Leptosomatum, Platy- comopsis, Rhabdodemania, and the majority of the species of Synon- chinae, Barbonematinae, and Platycominae. Arcuate spicules are charac- teristic of Cylicolaimus, Leptosomatides, Deontostoma, Thoracostoma, and Pseudocella. Filip’ev placed representatives of Anticomidae under the third type, namely, lamelliform spicules.
It seems to me that this scheme of classification is much too broad. Anticoma, placed by Filip’ev under the lamelliform type, includes a sig- nificant diversity of spicule shapes. In my material for this genus I found arcuate, broad, and lamelliform spicules, with the gubernaculum either situated ventrally, dorsally, or absent (Figure 12).
In Leptosomatum the spicular shape is fairly uniform. These organs are slightly curved, sometimes with a narrow capitulum, and widen in the anterior third; the gubernaculum is simple in structure (without processes) and dorsally situated. All the species of this genus may be grouped under spicules of the broad type. Platycomopsis is characterized by weakly curved spicules, broad in the distal half, and a ventrally situated guberna- culum. Species of Rhabdodemania have spicules similar to those of Leptosomatum; Barbonema and Platycoma have broad, tubular spicules; Cylicolaimus, Leptosomatides, Deontostoma, Thoracostoma, and Pseudo- cella have arcuate spicules. However, some species of Deontostoma, Thoracostoma, and Pseudocella have lamelliform spicules, namely, Deon- tostoma antarcticum, Thoracostoma setosum, and Pseudocella trichodes. This group is characterized by a complex gubernaculum which always has a dorsal and rarely a ventral process. Often the gubernaculum is paired and forms a ‘‘funnel” in which the distal part of the spicules is located. In Crenopharynx the spicules are rather unique; they are very slender and long with a small round capitulum, and a simple slitlike gubernaculum. Crenopharynx is close to species of the family Phanoder- matidae with respect to spicular structure.
Thus the structure of the copulatory apparatus within the limits of lower enoplids is highly diversified.
The sexual armature of the male, in addition to spicules, includes cop- ulatory papillae, setae, and an accessory organ. Papillae and setae are situated in two submedial rows in the anal region. Slightly anterior to the anus an unpaired glandular structure occurs, constituting an accessory organ. It resembles a large papilla externally but inside one finds rather
Figure 12. Types of spicular apparatus in lower Enoplida.
1 to 2—Leptosomatum; 3 to 4—Synonchus; 5—Deontostoma; 6—Thoracos- toma; 7—Pseudocella; 8—Cylicolaimus; 9 to 11—Anticoma; 12—Barbonema; 13—Platycoma; 14—Platycomopsis; 15—Crenopharynx; 16—Rhabdodemania.
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well-developed sclerotized tubes, annulations, or hemispheres. Sometimes sclerotized processes, directed downward or upward, are also present. The structure of the accessory organ and number and disposition of papil- lae and setae may serve as reliable species indexes. All these auxiliary copulatory armatures may be partially or fully absent. Representatives of Rhabdodemania and Leptosomatum lack setae, papillae, and accessory organs. In species of Anticoma an accessory organ of the tubular type is always present but setae and papillae absent. In species of Crenopharynx, on the contrary, accessory organs are absent but preanal setae invariably present. In Deontostoma, Thoracostoma, and Pseudocella an accessory organ, papillae, and setae are usually present. Very rarely papillae or setae may be atrophied but an accessory organ invariably developed. When all three are present, the structure of the accessory organ as well as the disposition of the papillae and setae may vary significantly. In Deontostoma arcticum papillae with setae commence near the anus and extend a fairly significant distance. The accessory organ is situated in the middle of this row of papillae. In Deontostoma papillatum the papillae bear no setae and commence not from the anus but from the accessory organ. Males of Deontostoma antarcticum have only an accessory organ; papillae and setae are totally atrophied in them. In Leptosomatum inocel- latum setae commence immediately behind the anus and papillae devoid of setae lie somewhat above the level of the accessory organ.
PHYLOGENETIC RELATIONS AND TAXONOMIC BASIS
Position of Order Enoplida in the Classification of Nematodes
The origin of nematodes and the position of their different groups in the taxonomic system of the class have yet to be conclusively resolved. Winslow (1960, p. 341) remarks that the position of nematodes in the classification of the animal kingdom and their phylogenetic relations have, as it were, slipped from the consciousness of researchers and hence their position is one of incertitude. In my opinion the latter contention is overly cautious. At present, most scientists engaged in the study of this group consider free-living marine nematodes extremely primitive and original forms (Filip’ev, 1921, 1934a; Schuurmans-Stekhoven, 1931; Hyman, 1951; Paramonov, 1962; and others). But Winslow is right that the question of the evolution of the class as a whole has yet to be fully resolved.
Researchers of this group have directed their attention mainly to parasitic nematodes and hence we now have considerable morphological, embryological, histological, and other data on this group. However, parasitic nematodes, being a specialized and highly organized group, can-
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not alone illuminate the evolution of this class. The answer to this ques- tion must be sought among the most primitive and less specialized group of nematodes. For this reason, before searching for affinities between nematodes and other groups of animals, it is essential to note relations between orders and families within the class per se.
I do not claim to have conclusively established these affiliations as the amount of anatomical and histological information available in literature is, to my regret, inadequate. Hence only preliminary observations regard- ing this problem are given.
Filip’ev (1921) rightly suggested that highly simple forms, which exhi- bit no features of reduction or (atrophy), should be considered the most primitive nematodes, since the evolution of this group followed a line of specialization and simplification of some organic systems. Such nema- todes belong to the order Enoplida.
Class Nematoda is divided into two subclasses—Secernentea compris- ing highly specialized and parasitic forms, and subclass Adenophorea in which mainly free-living forms, together with enoplids, a smaller number of parasitic nematodes, and phytonematodes are included. The families studied by me under the order Enoplida include exclusively marine forms. Of these families, Leptosomatidae comprises the least reduced and specialized group of nematodes with respect to structure and, for this reason, may probably be considered the most primitive family among free- living nematodes. The primitivity of this group is expressed in a number of anatomical and morphological peculiarities of structure.
The nervous system of nematodes of various groups is structured as follows. Around the nerve ring—the central part of the nervous system— nerve cells in species of Enoplida are situated in the most primitive man- ner; ganglia are totally absent and the nerve cells lie in a simple layer around the esophagus. In free-living nematodes of Monhysterida (Sipho- nolaimus, Solenolaimus) anatomically well defined, densely fused ganglia are present. In parasitic nematodes (Ascaris, Mermis, Ancylostoma) the Situation of the cells of the central nervous system reflects an intermediate position between these two groups, i.e., less well-defined ganglia repre- sented by only a group of cells. This is probably explained by a secondary reduction of the nervous system caused by a parasitic mode of life.
The peripheral nervous system has an extremely complex structure in species of Enoplida, while in free-living smaller forms, such as nema- todes of Monhysterida, this nervous system is quite simple. A similar phenomenon is observed in parasitic nematodes (Filip’ev, 1921).
Probably the original form of the nematode nervous system should be considered such a structure as is found in enoplids, where the degree of integration of the central nervous system is very minimal and the peri- pheral nervous system exhibits no features of reduction. In more highly
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organized free-living nematodes a distinct process of ganglionization, which leads to greater integration of the central nervous system, is ob- served. But reduction of the peripheral nervous system, brought about by the process of general reduction of cellular composition, accom- panies this. Reduction of the central and peripheral nervous systems of parasitic nematodes is effected by a parasitic mode of life. In addition to a weakly integrated central nervous system and a highly developed peri- pheral system, nematodes of the order Enoplida have the most primitively constructed organs of chemical sensitivity—the amphids—which are cyathiform in shape. Other orders of free-living nematodes have more complexly constructed amphids—round, horseshoe-shaped, or spiral.
The body cavity in various groups of nematodes is developed to differ- ent degrees. In leptosomatids, where it has not been seen by a number of authors (Jagerskidld, 1901; Tiirk, 1903; de Man, 1904; Timm, 1953), the body cavity is least developed. It is poorly developed in other families of the order Enoplida (Filip’ev, 1921). In other orders of free-living nema- todes it is present as a small slit and achieves fuller development in saprozoic forms and intestinal parasites (Filip’ev, 1937). Thus the near absence of a body cavity in leptosomatids also points to their lower stage of organization.
Within the limits of the class the process of oligomerization of a num- ber of organs has taken place (Dogel’, 1954). This process can be observ- ed by comparing the setaceous armature of free-living and parasitic nematodes.
Setae are extremely numerous and best developed in free-living nema- todes, especially in marine forms (Filip’ev, 1918, 1921; Dogel’, 1954). In parasitic forms they are considerably reduced. The original number of cephalic sensory organs of nematodes should be taken as six labial papillae and a crown of ten cephalic setae. In parasitic forms (Ascaridata, Spirurata, and others) the number of papillae and setae decreases either as a result of fusion or as a result of reduction. In free-living nematodes, in addition to cephalic setae, other setae are scattered all over the body or at least over the anterior end. In nematodes of the order Enoplida the crown of cephalic setae is usually situated in a single circle; in some species these setae are equal in length, while in others the four sublateral setae may be longer than the others. Only in Oxystomatidae is the crown of cephalic setae distinguished by two types—anterior, comprising six shorter setae, and posterior, comprising four relatively longer setae.
Beyond the limits of the order Enoplida the crown of cephalic setae has undergone more significant change. In most nematodes of the orders Chromadorida and Monhysterida the anterior crown bears structures resembling papillae and the posterior crown comprises four setae. In some nematodes of the order Desmoscolecida the four setae of the second
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circle resemble cornuate processes. In some Chromadorida and Desmo- scolecida a number of setae situated on the body merge with each other, forming powerful and strictly localized setae employed for locomotion. Preanal setae in some Desmoscolecida fuse and acquire the significance of copulatory setae. Thus, on the basis of the foregoing examples, one can distinctly trace the change of function and oligomerization of setae which originally had a sensory function.
In most species of Enoplida, especially in lower representatives, the cephalic crown of setae has a much simpler, nonproliferative structure, and the setae on the body are numerous and irregularly scattered. All these setae have only a sensory function. Such a type of arrangement of setae in nematodes is apparently more primitive.
Dermal glands are also subject to oligomerization. These glands are numerous within Leptosomatidae, while only a lone cervical gland is seen in Anticomidae.
Oligomerization can also be seen in the reproductive system. Paired reflexed gonads, paired genital ducts, and paired uteri fusing only near the genital pore should be considered the original form in nematodes. A reduction in the reproductive system takes place within the limits of the class. The commencement of this process is already evident in Enoplida, in some species of Oncholaimus (Filip’ev, 1921) where one female genital tube is significantly shorter than the other. In some cases even complete atrophy of one of the female genital tubes is seen. More often the ante- rior genital tube (Oncholaimidae) is reduced and less often the posterior genital tube (Oxystominidae).
No sign of reduction or fusion of organs is observed in the structure of the reproductive system of female leptosomatids and anticomids. Since no gonadal reduction or fusion of the reproductive tubes has occurred in them, the gonads are always reflexed. More often a single unpaired female genital tube is found in parasitic nematodes, but the phenomenon of polymerization may also be observed exceptionally. Thus there are four genital tubes in Polydelphis, six in Hexametra, and even nine to eleven in Turgida. This is considered quite natural for parasitic forms in connection with the need to produce a large number of eggs.
Paired gonads are extremely rare among males compared to females. Thus in Chromadorida males with a single testis are more common, in Monhysterida the testis may be single or paired, in Enoplida the testes are generally paired, but in lower groups of this order they are always paired. The genital ducts (vas deferens and ejaculatory duct) are always unpaired in males. Sometimes oligomerization is evident in even the male copulatory apparatus; of the two spicules, one may be atrophied, which is mostly observed in parasitic nematodes.
Thus the female and male reproductive systems in leptosomatids are
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least reduced and hence this group is considered much more primitive than the remaining groups of nematodes.
Phagocytic cells in nematodes of Enoplida are usually very numerous and scattered irregularly over the body. Their number in Leptosomatidae and Oncholaimidae ranges from 150 to 220 or more, and in Enchelidiidae never more than 70. Their structure and situation in enchelidiids are similar to those in oncholaimids. A more regular disposition of these cells is seen in Oxystominidae, where they concentrate near the lateral fields (Biitschli, 1874; de Man, 1907). In most leptosomatids the phago- cytic cells are numerous and scattered irregularly over the body, but in Leptosomatides euxina they are situated mainly along the ventral line. In species of Chromadorida these cells are arranged in a few longitudinal rows (up to eight in number). In Araeolaimida the number of phagocytic cells is considerably reduced; in Axonolaimus setosus there are only two phagocytic cell (Filip’ev, 1918, 1921).
Extremely numerous and irregularly scattered phagocytic cells are thus found in enoplids.
It is interesting to review the changes in cellular composition of indi- vidual organs and tissues of nematodes. In nematodes of the order Eno- plida eight cords formed by the hypoderm may be present; these cords invariably project. Submedian cords vary in number and may be absent in some species (Filip’ev, 1921). In such cases the total number of cords may decrease to four. In more highly organized free-living and parasitic nematodes the number of these cords is always constant and equal to four. Fluctuations in cellular composition of the lateral cords have been observed in Leptosomatidae. In Synonchus strasseni three to five rows of cells have been recorded (Tiirk, 1903), in Thoracostoma setosum five to Six rows in the median cords (de Man, 1904), and in Leptosomatum ace- phalatum four to five rows in the lateral cords (Timm, 1953). Filip’ev (1916) relates the number of cellular rows in the hypodermal cords to the change in number of cells in other organs. The number of intestinal cells in different nematodes varies considerably (Biitschli, 1873; de Man, 1888; Maupas, 1900; Filip’ev, 1918, 1921; Timm, 1953). Their number is maxi- mal in Leptosomatidae and Oncholaimidae of the order Enoplida and minimal in the orders Chromadorida and Monhysterida. In many mon- hysterids the intestine consists in all of one or two rows of cells. It should be noted that besides the large number of cells constituting the intestine in enoplids, Timm (1953) has observed considerable variation in the number of cells within the limits of species in some leptosomatids.
In the muscular fields situated between the hypodermal cords cellular composition also varies. As is well known, all members of the order Eno- plida belong to the polymyarian group, i.e., a large number of cells occur in each muscular field. The majority of free-living nematodes also belong
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to this group. Enoplids have a very large number of cells in the muscular
elds (up to 12; Timm, 1953). A small number of free-living nema- todes—Monhysteridae and Rhabditoides—and parasitic nematodes be- long to the meromyarian group. Even a total degeneration of muscles (Filip’ev, 1934) has taken place in phytonematodes of the genera Hetero- dera and Allantonema. The same phenomenon has been observed in Meloidogyne. ,
During ontogenesis all nematodes pass through the stage of mero-
myarian musculature when the number of muscle cells is constant (Mar-
36 tini, 1903, 1906). By preserving this stage, adult meromyarian nematodes with a constant number of cells develop (Martini, 1908). With the multi- plication of muscle cells the polymyarian type is obtained. It seems to me that Filip’ev is absolutely right in his assertion that it would be erro- neous to consider young meromyarian individuals the ancestors of all meromyarian forms. Meromyarian forms should be cosidered regressive or neotenic but not primitive.
To summarize, of all these orders enoplids are the lowest organized group: cuticle smooth and totally devoid of protective armature of any kind; cephalic setae usually situated in one circle; amphids cyathiform; nervous system simple; and esophagus devoid of diverticula. Such fea- tures indicate the primitive structure of enoplids.
Taxonomy and Phylogenetic Relation of Families of Order Enoplida
To understand the problem of the taxonomic position of families of the order Enoplida attention should be given to the differences observed by Inglis in the cephalic structure and oral cavity of Leptosomatidae and Anticomidae on the one hand, and most representatives of the order on the other. In representatives of Leptosomatidae, especially higher ones such as Thoracostoma, the buccal cavity is poorly expressed and is not topographically demarcated from the onchial cavity; consequently the onchia are displaced far toward the anterior end and situated almost at the level of the odontia. Supporting structures, if developed, form as processes of the cephalic capsule. Because of the fusion of the buccal and onchial cavities and the anterior position of the onchia, the specialized musculature of the esophagus extends far forward toward the bases of the onchia, where it is attached after crossing the cephalic bladder. Non- specialized musculature in the posterior part of the esophagus remains undifferentiated, which is expressed exteriorly in the nonalveolar appear- ance of the esophagus. The same is observed in representatives of Anti- comidae; the only differences are that the cephalic capsule and oral cavity with all its armature are weakly expressed.
An entirely different picture is seen in representatives of Phanoder-
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matidae, Enoplidae, Oncholaimidae, and Enchelidiidae. Here the oral cavity is distinctly differentiated topographically into the anterior buccal cavity and the posterior onchial cavity; buccal rods may be situated in the former which play the role of supporting structures or develop later into mandibles, while in the posteriorly situated onchial cavity these rhabdoid structures develop into onchia. The sclerotized lining of both cavities may fuse imperceptibly, forming onchiobuccal plates, to the pos- terior (onchial) half of which the specialized musculature is attached, ensuring movement of the entire complex. Due to the posterior position of the onchia, the specialized musculature does not extend to the poste- rior margin of the buccal cavity and, consequently, does not cross the cephalic bladder. The nonspecialized musculature of the posterior part of the esophagus is differentiated into separate fascicles which externally impart an alveolar appearance to this part of the esophagus.
For a clear-cut picture of these undoubtedly independent lines of evolutionary development, one must imagine the structure of a hypothe- tical form which could have been their common ancestor. The cephalic capsule of such a form should resemble a cap at the anterior end of the body, i.e., of that part where the musculature of the esophagus joins the body wall. The cephalic and esophageal capsules in this form should not be differentiated and the cephalic bladder should be absent. The trira- dial internal lumen of the esophagus should open abruptly as a triangular oral opening so that there would be practically no buccal cavity. The lumen in the anterior part of the esophagus should remain constant in diameter throughout its entire length so that, strictly speaking, there would be no onchial cavity. Here, one could project that part of the eso- phagus would later develop into the onchial cavity. Because of the com- plete absence of oral armature, there would be no need for specialized musculature. The musculature of the esophagus would remain undiffer- entiated throughout its length.
Such a hypothetical form*is very similar to members of the genus Leptosomatum. This gives one grounds for assuming the first evolutionary line (Leptosomatidae, Anticomidae, and Oxystominidae) or their primi- tive representatives as ancestral in relation to the second line, i.e., Eno- plidae, Phanodermatidae, and others. Since it is indisputable that such forms as Leptosomatum are the most primitive within the limits of the first evolutionary line, it is clear that Leptosomatidae is the most primitive in this order.
In the order Enoplida, in addition to the families studied by Inglis (1964), there are other families related to these two phylogenetic branches; unfortunately information about them is absolutely inadequate to judge their taxonomic position. Of the two families grouped under the super- family Tripiloidea and often considered the most primitive in the order
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(de Coninck, 1965), Ironidae belongs to the leptosomatid—anticomid branch (Inglis, 1964). Tripilidae cannot be regarded as the most primi- tive in the order due to the presence of some specialized peculiarities of the esophagus, in particular the development of the esophago-intestinal valve. Lauratonematidae also cannot be regarded as primitive due to the reduction of the posterior gonad in males, and the annulated nature of its cuticle; the latter is uncharacteristic of representatives of the order as a whole.
If the evolution of the head in Leptosomatidae is examined, two parallel, but to some extent independent, processes can be traced. The first process is intensification of development of the cephalic and esopha- geal capsule, and the second process the formation and development of the oral cavity. The initial stages of the first process can be traced among genera close to Leptosomatum. In Leptosomatides and Paraleptosomatides the cephalic capsule is developed more powerfully than in Leptosomatum and there is every reason to assume that a developed cephalic bladder is also present. Moreover, in Leptosomatides conisetosum a depression occurs in the posterior margin in which the cephalic setae are situated. In Leptosomatum reducta there are outgrowths in the cephalic capsule resembling the supporting structures observed by Inglis in some of the forms studied by him. The commencement of the second process—devel- opment of the oral cavity—is also evident to some extent in nematodes of the group Leptosomatum. Mawson (1956, 1958b) observed a distinct oral cavity in Leptosomatides conisetosum. Both of these processes are developed in genera clustering around Synonchus and Thoracostoma. Genera of this group have a powerful cephalic capsule or often support- ing structures in the anterior part. Sometimes they have a cephalic cap- sule continuing strongly backward or uniting in this part with the cervical capsule, which has deep clefts along its posterior margin. Representatives of these genera also have a fully developed esophageal capsule and a con- spicuous cephalic bladder which is usually divided into six parts by the radii of the esophagus and fascicles of specialized musculature. At the same time they have an oral cavity in which onchia and odontia are pre- sent. True, the oral cavity is rather small in size.
In the other group of genera, those close to Cylicolaimus, the cephalic capsule has not attained the significant development seen in the previous group, and at best resembles the cephalic capsule of some species of Lep- tosomatides. Contrarily, here the oral cavity is quite well developed (at least in males of those genera exhibiting sexual dimorphism). Moreover, widening of the oral cavity has taken place mainly at the expense of the onchial cavity, while the buccal cavity retains a relatively insignificant depth. Concomitantly, some peculiar types of cephalic bladder are seen; the bladder may extend significantly along the body but be reduced to a
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narrow ring between the large oral cavity and the body wall. Structures such as odontia sometimes develop in the anterior part of the oral cavity; large onchia are situated somewhat posteriorly. The absence of onchia is probably explained by their wearing out since otherwise the reason for the development of an extensive onchial section in the oral cavity would not be understandable.
Thus three distinctly defined groups of genera, of which one is pri- mary and the other two derived independently from it, are observed in Leptosomatidae.
Sometimes the genus Triodontolaimus, with only a single species— Triodontolaimus acutus (Villot)—is placed as a subfamily, in addition to the group of genera discussed above, in the family Leptosomatidae. The problem of its phylogenetic connection with the present Leptosomatidae is fairly complex. Judging from the description of de Man (1893, p. 116), the cephalic capsule in T. acutus is absent or at best very poorly devel- oped. On the basis of his description, one can only gather that the head is posteriorly limited and demarcated from the rest of the body by a thin suture (p. 116); unfortunately this suture is not depicted in the illustra- tions. de Man makes no mention of the esophageal capsule, directing his attention to the presence of three symmetrical ‘‘teeth”’ with wide and concave bases. Subsequent information, namely, that musculature binds these bases, makes one assume that these “‘teeth’’ are onchia. The shift- ing forward of the onchia and the indivisibility of the small oral capsule indisputably indicate the relation of Triodontolaimus to the phylogenetic branch, Leptosomatidae—Oxystominidae. Simultaneously, the combi- nation of peculiarities noted above (weak development of the cephalic capsule and powerfully developed onchia located in a comparatively small oral cavity) compel one to assume that Triodontolaimus is an ex- tremely unique lateral offshoot of this phylogenetic branch. Hence it cannot be included in Leptosomatidae and merits isolation in an inde- pendent family. Because information on the morphology of Triodonto- laimus is so meager, it seems more appropriate to assume that this group is derived from extremely primitive representatives of the family Lepto- somatidae.
To solve the problem of the position of the family Anticomidae, it is necessary to establish whether the structural simplicity of the cephalic end is primary or simply the result of secondary simplification. An exa- mination of the main group of genera of this family, clustering around Anticoma, revealed that some forms, such as Cephalanticoma chitwoodi (Inglis, 1964), possess an adequately developed cephalic capsule, a poor- ly developed cephalic bladder, and a small oral cavity with distinct onchia. In Odontanticoma the cephalic capsule is almost negligible but the oral cavity well developed (apparently at the cost of its onchial part).
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These peculiarities, in association with small size, seem to indicate that the structural simplicity of the anticomid head is the result of secondary simplification due to general reduction in size. The presence of a renette also bespeaks the phylogenetic advancement of anticomids. The genus Parabarbonema, with only one species—P. barba Inglis, 1964—occupies an intermediate position between anticomids and leptosomatids. The structure of the cephalic capsule in this species is almost identical to that in members of Leptosomatides. The oral cavity is small and armed with three large onchia. Thus the anterior end of the body of anticomids could be regarded as the end result of simplification of the form type Parabar- bonema. Parabarbonema is distinguished from Anticoma by the absence of a renette.
The taxonomic position of the other two groups of genera, clustered around Platycoma and Barbonema, is not really clear since information concerning these two genera is very scanty. Nevertheless both groups contain representatives with a highly reduced or even totally reduced cephalic capsule and an extremely small oral cavity; however, small but distinct onchia are present in Proplatycoma sudafricana (Inglis, 1964). Furthermore, one cannot refrain from mentioning the well-known re- semblance in spicule structure in Parabarbonema and Barbonema.
Until fuller elucidation of the peculiarities of various anatomical char- acters is forthcoming, it is better to consider genera clustered around Platycoma and Barbonema independent of Anticoma and genera close to it, and also independent of ancestors analogous to Parabarbonema. The absence of a renette in Parabarbonema bespeaks the possibility of keeping Anticoma and genera close to it isolated in contrast to other genera in this family. If leptosomatids progressed along the path of complexity of the cephalic capsule and oral cavity, anticomids retrogressed along the path of simplification of these structures which, among other reasons, confirms the evolutionary independence of the family.
Two groups included by a number of authors in the composition of the family Leptosomatidae have been deliberately omitted by me in the foregoing discussion. Rhabdodemania has been variously included in the family Leptosomatidae (Filip’ev 1927; Schulz, 1932; Schuurmans-Stekho- ven, 1946; Schuurmans-Stekhoven and Mawson, 1955), Oncholaimidae (Southern, 1914; Ditlevsen, 1926), Enoplidae (Wieser, 1959; Inglis, 1964; de Coninck, 1965), and sometimes established as an independent family (Filip’ev, 1934). As shown by Inglis (1964), Rhabdodemania belongs to the evolutionary branch Phanodermatidae-Enoplidae on the basis of structure of the anterior end of the body, and consequently must be ex- cluded from the family Leptosomatidae. However, it is not easy to estab- lish the position of this genus within the limits of the phylogenetic branch. Inglis (1964) in transferring this genus to Enoplidae, understood by him
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in a very broad sense, notes features of its similarity with the family Enchelidiidae. Contrarily, de Coninck (1965) aligns Rhabdodemania with the family Enoplidae in a special subfamily, Rhabdodemaniinae, includ- ing therein the genera Chaetonema, Trichenoplus, Trileptium, and Donsi- nema. In my opinion, the latter four genera have very little in common with Rhabdodemania in the construction of the anterior end of the body. I think it is more appropriate to isolate Rhabdodemania as a separate group (separate family), occupying a somewhat intermediate position among enoplids with unequal onchia (Saveljevia, Parasaveljevia, Oxy- onchus), i.e., between Oncholaimidae and Enchelidiidae.
The taxonomic position of the genus Crenopharynx merits special discussion. Species now related to this genus were earlier included in Stenolaimus (Filip’ev 1927; Schuurmans-Stekhoven, 1950), and usually placed close to Anticoma or even listed as its synonym. Filip’ev (1934) suggested the name Crenopharynx for that group of species which has characters in common with Stenolaimus and placed the genus in Phano- dermatidae (Filip’ev, 1927). Subsequently many authors related the genus Crenopharynx to the family Phanodermatidae, guided by the predomi- nantly alveolar structure of the esophagus. Inglis (1964) showed that the structures of the buccal cavity of Phanodermatidae and Enoplidae were homologous through a detailed analysis of the cephalic structure of Cre- nopharynx eina. On these grounds he emphasized the need for including Crenopharynx in Phanodermatidae. However, this inclusion is improper. The homologue only proves the affinity of this genus to the phylogenetic line Phanodermatidae—Enoplidae and does not substantiate its inclusion
40 in either family. Crenopharynx can be sharply distinguished from present- day Phanodermatidae, type Phanoderma, as well as the aberrant genus Dayellus isolated by me in a separate family, by the presence of a trian- gular oral opening, primitive cephalic capsule with undeveloped cephalic bladder, and shallow buccal cavity devoid of distinctly formed buccal styli. Hence one is compelled to isolate Crenopharynx in an independent family to which it seems to me, the genus Nasinema should also be trans- ferred. The genus Nasinema was formerly included by Filip’ev in Phano- dermatidae.
The structure of the head, oral cavity, esophagus (alveolar in the posterior half), and general shape of the body bring Nasinema and Cre- nopharynx close together.
Representatives of the family Crenopharyngidae occupy, apparently, a much lower position in the phylogenetic branch to which they belong. Such an interpretation explains the similarity in structure of the cephalic end of Crenopharyngidae and Anticomidae. A poorly developed cephalic capsule and oral cavity are found so often among anticomids and lower leptosomatids that the similarity of these features cannot be overlooked.
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Taxonomy of Family Leptosomatidae
The family Leptosomatidae was first established as a subfamily of Enoplidae by Filip’ev in his works of 1916 and 1918 to 1921 and only later raised to the rank of family (de Coninck and Schuurmans-Stekho- ven, 1933).
Leptosomatidae comprises a primitive group of free-living marine nematodes with poorly expressed features of specialization. Filip’ev (1927) has stated that the specialization of this family is of such a low order that leptosomatids do not represent a single group but rather a series of isolated genera. However, descriptions of genera of Leptosoma- tidae since 1930 have directed my thoughts not to isolated genera, but to distinct groups of genera. It seems to me that these groups would be better classified as separate subfamilies.
Leptosomatinae, an extremely primitive subfamily, includes the genera Leptosomatum, Leptosomatides, Leptosomella, Leptosomatina, and Paraleptosomatides for which a short cephalic capsule with relatively fine walls and a narrow cephalic ring are characteristic. The oral cavity is absent. In most of these genera the tail is short and bluntly rounded. Leptosomella has a rather long and conical tail which narrows soon after the anus. Extremely short cephalic setae are also characteristic of this group. Usually the cervical setae, if present, are short. Only Leptoso- matina Allgen, 1951 and Leptosomella Filip’ev 1927, which probably will be combined in the future due to many features of similarity, have long cephalic setae. It is regrettable that Filip’ev described his genus only on the basis of females and Allgen on the basis of males. As the material of these two genera was not available to me I cannot propose their combin- ation at present and tentatively treat Leptosomatina and Leptosomella as independent genera.
In speaking about the merger of these two genera I have in view their type species—Leptosomella acrocerca and Leptosomatina longisetum re- spectively. They are very close in such characters as shape of head, pre- sence of long cephalic setae, absence of eyes, thick cuticle, and absence of cervical setae. These very characters have been given by the authors as diagnostic features of the genera. Allgen later (1958a) described another species of Leptosomatina, namely, L. appendixocaudatum, in which the cephalic structure is entirely different from that in L. longise- tum, and for which extremely short cephalic setae and an accessory organ of unique structure are characteristic (latter absent in L. Jongisetum). The differences between L. longisetum, and L. appendixocaudatum appear to me so incomparably greater than the differences between Leptosomatina longisetum and Leptosomella acrocera that a study of supplementary material will no doubt lead to their combination in one genus and the
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isolation of Leptosomatina appendixocaudatum in an independent genus.
Of all the genera belonging to this group, Leptosomatum has the sim- plest spicular apparatus, i.e., weakly curved spicules and simple guberna- culum devoid of processes. All the remaining genera have a gubernacu- lum provided with a process, which may be only dorsal or dorsal and ventral.
Thoracostomatinae, isolated by de Coninck (1965), is characterized first and foremost by a highly developed cephalic capsule. It includes such genera as Thoracostoma, Deontostoma, Pseudocella, and Synonchus with genera close to it. The genus Synonchus originally embraced so many varied forms that many authors had a tendency, totally justified, to divide it into several subgenera. A contrary attempt to unite all forms with a well-developed cephalic capsule and clavate tail created much confusion in the taxonomy of this group. The fact that a series of species were transferred to Thoracostoma and some even to Leptosomatum (Villot, 1875) on the basis of the structure of the cephalic capsule, exacerbated this confusion. Cobb (1893a, p. 411) described the genus Synonchus as follows: ‘“‘Worms of this genus are closely related to those of Oncholai- mus. They have a pharynx armed with teeth in which the dorsal one is predominant and the remainder rudimentary. The pharynx is so small . that the teeth occupy almost all the space when the mouth is closed... . A ventral accessory organ is present in males anterior to the anus.’ A detailed description of the two species of this genus—S. hirsutus and S. fasciculatus—came later.
Linstow (1900) described the Artic species Enoplus edentatus in which the oral capsule lacks sclerotized plates and teeth, which characterize representatives of this genus. Due to the absence of the most distinctive character of the genus Enoplus, namely, sclerotized jaws, Jagerskidld (1901) considered it improper to include this species in Enoplus and trans- ferred it to Thoracostoma. He also gave a detailed description of a new species, Thoracostoma acuticaudata, but observed that he was relating it to Thoracostoma only tentatively, suggesting that future studies might isolate it in an independent genus. de Man (1904) held the same point of view. Tiirk (1903) gave a detailed description of two Neapolitan species which he included in Thoracostoma. Southern (1914) described two species from the southern coast of Ireland and assigned them to a new genus, Fiacra—F. brevisetosa and F. longisetosa. He considered the genus established by him close to Thoracostoma, Enoplus, and Tridontolai- mus, and conceded that with future studies his species might have to be transferred to two different genera.
Filip’ev (1916) suggested the combination of all species with a conical tail, described as Thoracostoma, in a new genus—Jaegerskioeldia—with the type species Thoracostoma acuticaudata (Jagerskidld). Later Filip’ev
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(1927), acknowledging he had not known earlier about Cobb’s descrip- tion of the genus Synonchus (Cobb, 1893a), accepted the synonymy of these genera. Observing the great diversity of species in this genus, Filip’ev (1927) divided it into three subgenera: 1) Fiacra [type species, S. (F.) longisetosum] with long cephalic setae, large amphids, large arcuate spicules, and labial teeth; 2) Synonchus s. str. [type species, S. (S.) fasci- culatus| with cephalic setae of average size, large amphids, large spicules, and without labial teeth; and 3) Jaegerskioeldia [type species, S. (J.). acuticaudata] with extremely short cephalic setae, small amphids, short spicules, and without labial teeth.
Quite recently it has been suggested (de Coninck, 1965) that these subgenera be elevated to independent genera. On studying those forms which constitute the genus Synonchus in its new dimensions, I have arriv- ed at the conclusion that the latter is a composite group but undoubtedly liable to division into a series of genera. Thus, in addition to isolating the above-mentioned Synonchus, Fiacra, and Jaegerskioeldia, I also iso- late Eusynonchus (type species, Fiacra brevisetosa), Tuerkiana (type species, Thoracostoma strasseni), and Paratuerkiana (type species, Thora- costoma comes), the descriptions of which are given in the taxonomic part of this work.
Thoracostoma (Synonchoides) galatheae, described by Wieser (1956), combines characters of Synonchus (short cephalic capsule and buccal capsule with triangular plates) and Thoracostoma (shape of tail). As such, the form is isolated here in the subgenus Synonchoides of the genus Thora- costoma, stipulating that future studies will probably elevate it to the rank of genus. Another subgenus, Corythostoma, described by Wieser in the same work, also deserves in my opinion to be raised to the rank of genus as it differs notably from Thoracostoma in the structure of its cephalic capsule. The cephalic capsule of Corythostoma is wide and short with extremely wide, uniform interlobular grooves. The lateral grooves are not distinguishable in any way from the subventral and subdorsal grooves.
I propose that all the genera enumerated above be combined in the subfamily Synonchinae of the family Leptosomatidae. Macronchus Inglis, 1964 should also be transferred here; the author himself expressed doubts about its affinity with Synonchus. Finally, Anivanema, described by me in the present work, has likewise been placed in the family Leptosoma- tidae.
The history of the genus Thoracostoma warrants review. This genus was established by Marion in 1870 for four species from the Mediterra- nean Sea: T. echinodon, T. dorylaimus, T. montredonense, and T. zolae. To this genus Marion assigned worms with a long, almost nonattenuated body, with a sharply truncated head and a short tail. The presence of
4
Ww
53
permanent eyes and the absence of an accessory organ in the genital ap- paratus of the male (papillae present instead) are also characteristic of the genus, but a sclerotized cephalic capsule is the most important diag- nostic feature. Species which had earlier been assigned to different genera—Hemipsilus (Leuckart, 1849), Enoplus (Eberth, 1863; Schneider, 1866), and Leptosomatum (Bastian, 1865; Villot, 1875)—were subsequ- ently included in this genus. Later all nematodes with a sclerotized cephalic capsule were likewise included in the genus Thoracostoma. The significant difference in the structure of cephalic capsules compelled taxonomists to subsequently define a series of independent genera in Leptosomatidae, namely, Tridontolaimus de Man, 1893; Rhabdodemania Baylis and Daubney, 1926; Synonchus (Jaegerskioeldia) Filipjev, 1916; Platycoma Cobb, 1893; Metacylicolaimus Stekhoven, 1946; Cylicolaimus de Man, 1890; Synonchus Cobb, 1893; Deontostoma Filipjev, 1916; Leptosomatides Filipjev, 1918; and also a genus already placed in another family—Phanoderma Bastian, 1865.
At the commencement of the twentieth century the limits of Thoraco- stoma were more or less firmly established. In 1916 Filip’ev isolated from Thoracostoma a new genus—Deontostoma. Filip’ev regarded the presence of a ventral process in the cephalic capsule of Thoracostoma and its ab- sence in Deontostoma one of the basic differences between these two genera. He labeled this process rather inappropriately the ‘‘ventral tooth.” This term misled foreign authors (Wieser, 1953c; Mawson, 1958a) and hence they refused to recognize the independence of genus Deontostoma.
On the basis of a thorough study of the work of Filip’ev and the material at my disposal, I consider it necessary to restore the indepen- dence of the genus isolated by Filip’ev (Platonova, 1962). The genus Deontostoma differs significantly from Thoracostoma in cephalic structure as well as in structure of the spicular apparatus. The cephalic capsule of representatives of Deontostoma is almost equal in width near the top and base and its entire wall is of the same thickness; as a result it has a radi- ally symmetrical structure and appears symmetrical in a lateral view. In representatives of Thoracostoma the cephalic capsule narrows consider- ably from the base to the top; its ventral wall is significantly longer and thicker than the dorsal wall and due to this fact the capsule has a bilateral symmetrical structure and appears asymmetrical in a lateral view.
The spicules of males of Deontostoma are rather uniformly curved in their proximal part and devoid of sharp angles and grooves. The guber- naculum has distinct dorsal and ventral processes which are joined together by a curved plate. When they fuse, the halves of the guberna- culum form a sort of funnel in which the distal parts of the spicules lie. In Thoracostoma the spicules have a sharp break approximately midlength
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and a velum often occurs on their internal margin. The terminal part of the gubernaculum encloses the distal end of the spicules. The processes of the gubernaculum are directed dorsally and although closely apposed to the spicule body are situated at a sharp angle to it.
These are the most distinctive characters differentiating Deontostoma and Thoracostoma. Several minor characters are detailed below.
Filip’ev (1927) divided Thoracostoma into two subgenera—Thoraco- stoma s. str. and Pseudocella. He related nematodes with distinct photo- sensitive eyes and the above-described spicular structure to subgenus Thoracostoma. To the subgenus Pseudocella he transferred species com- pletely devoid of photosensitive pigment, or with pigment scattered throughout the anterior end of the body, or very rarely species with eyes always devoid of a lens. The spicules in this subgenus are smoothly arcuate and notably narrower than those of the subgenus Thoracostoma s. str. The gubernaculum has a caudal process directed at right angles to the longitudinal axis of the spicules. Filip’ev predicted that these two subgenera would be elevated to independent genera with the passage of time. Wieser (1956) notes that the structure of the spicular apparatus is a much more important character for the division of these two subgenera than the presence or absence of photosensitive organs. since in all cases the latter may be totally absent even in Thoracostoma s. str.
A study of the species of Pseudocella permits me to supplement the diagnosis of this subgenus given by Filip’ev. All three genera are com- bined in a single subfamily, Thoracostominae, of the family Leptoso- matidae.
If leptosomatids of the subfamily Thoracostominae reveal a tendency toward greater complexity of the cephalic capsule, then the genera Cylicoliamus, Ritenbenkia, and Metacylicoliamus exhibit complexity of the oral capsule. In this group together with greater complexity of the cephalic capsule, developed significantly less however than in Thoraco- stominae, one finds a powerful oral capsule with a thick sclerotized lining armed with onchia. Representatives of Metacylicolaimus have a relatively wide but not very deep oral cavity in which blunt onchia jut out. In Ritenbenkia the oral cavity is significantly longer than that in the previous genus, its wall much thicker, and the onchia and sclerotized plates arrang- ed around the oral opening. Maximum development of the oral cavity occurs in Cylicolaimus, where it is very extensive, thick-walled, and usually armed with large teeth situated in its depth.
Such a characteristic feature as the presence of a highly developed
‘oral cavity and associated changes in the structure of the head permit one
to combine the above-mentioned genera with Paracylicolaimus in the subfamily Cylicolaiminae.
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Taxonomy of Family Anticomidae
Like leptosomatids, anticomids were also isolated in a separate sub- family within Enoplidae by Filip’ev in his works of 1916 and 1918 to 1921. In much later works (1927, 1934) Filip’ev transferred the genus Anticoma to Leptosomatinae. de Coninck (1965) assigned Anticominae to the family Leptosomatidae but Hope and Murphy (1972) raised it to the rank of a family.
The family Anticomidae includes many diverse genera that can be grouped into different subfamilies. The genera Anticoma, Paranticoma, and Anticomopsis, as well as Cephalanticoma and Odontanticoma, newly described in the present work, Antopus (with a single species, A. serialis) and Stenolaimus (with a single species, S. Jepturus) can all be included in Anticominae.
For a long time Stenolaimus occupied in extremely uncertain position in the classification of Anticomidae. Filip’ev (1934), conceding its hete- rogeneity, proposed S. /epturus as a synonym for Anticoma and proposed the genus Crenopharynx for the species Stenolaimus marioni, retaining it in the family Phanodermatidae. I agree with this concept only because this genus really is in need of a similar division into two independent genera. But Stenolaimus lepturus considerably differs from the genus Anticoma in structure of the spicules and situation and number of cervical setae, and must indisputably be regarded as an independent genus of the subfamily Anticominae. The position of Crenopharynx has already been discussed.
Barbonema and Parabarbonema differ so much from each other that each deserves isolation in a special subfamily—Barbonematinae and Parabarbonematinae.
Platycoma and Platycomopsis should also constitute a separate sub- family.
ECOLOGY
The ecology of free-living nematodes has been studied little and needs special attention and collection of material. As the basic purpose of this work is the taxonomic revision of the lower Enoplida, I had to utilize to some extent the casual and fragmentary information available while examining some problems regarding the ecology of this group.
The opinion that free-living nematodes were highly eurybiont prevail- ed among nematologists for many years. Kreis (1934) proposed that while inhabiting those parts of the sea which are advantageous to their existence, these nematodes do not exhibit a distinct affinity for definitive biotopes. This means that one and the same nematode species may be
56
found at different depths and in entirely different conditions, inhabiting littoral aquatic plants and sublittoral silts nonselectively.
Schuurmans-Stekhoven (1931) studied the nematode fauna of the North Sea and Zuider Zee and discovered a large number of euryhaline forms among these organisms.
Gerlach (1958) notes that differences in biotopes with respect to fauna of free-living marine nematodes are not large; this fauna lives mainly in sandy beds and sublittoral facies. He thinks that the major percentage of
45 these species are eurybionts. Gerlach, however, has noted a rather signi- ficant difference in nematodes in the littoral zone on the basis of biotopes.
It has also been established by Gerlach (1953, 1958) and Wieser (1951, 1953, 1960) that the distribution of nematodes reflects not so much a variety of biotopes, as a peculiarity in substratum, in particular the degree of its disintegration. In the distribution of nematodes on the basis of their association with various types of algae, species affinity of algae is not so significant as its external form, size, and degree of fragmentation of thallus. The same may be said about the substratum. Silt, fine sand, pebbles, and coarse sand should be examined first of all for the presence of interstices which may serve as shelters for the worms (p. 324).
Wieser (1953) has given an interesting ecological classification of free- living nematodes. It is based on the structure of the oral apparatus, which reflects the nature of feeding and consequently to some extent the type of life led by these organisms. All free-living nematodes are divided by Wieser into four groups (Figure 13).
Figure 13. Types of structure of the oral cavity of nematodes (from Wieser, 1953b).
1] A—Anticoma,; 1B—Paramonhystera; 2A—Microlaimus; 2B—Enoploides.
1. Group 1A. Forms lacking a distinct oral cavity and any kind of oral armature. Type of feeding, simply sucking with the help of the esophageal muscles. Food, detritus consisting of fine soft particles. Thrive among algae in the littoral zone and soft beds in the sublittoral.
2. Group 1B. Forms with well-developed cyathiform, conical, or cylindrical oral cavity which, like the previous group, are also devoid of an oral armature. Feeding asin group 1A. In addition, intake of detritus
46
=)//
effected by movement of lips and mouth. Food, detritus consisting of larger particle (including diatoms), Inhabit soft sand rich in detritus.
3. Group 2A. Oral cavity well-developed and armed with small scle- rotized denticles or plates. Nematodes capable of scraping the surface of algae or piercing their membrane to suck cellular sap. Food, epiphytes and algae. Inhabit almost all biotopes.
4. Group 2B. Oral cavity large with a powerful armature of different types. Feeding as in the previous group but most of these nematodes are predators, swallowing small organisms, including other nematodes. Live in the littoral zone in coarse sand poor in detritus, and the sublittoral among shells and sand with larger particles.
Species of Leptosomatidae and Anticomidae play a significant role in the fauna of free-living marine nematodes. The number of their species ranges from 5 to 46 (or from 2 to 19% in relation to the total number of nematodes studied). My data and that collected from literature is present- ed in the Table which follows.
In some cases leptosomatids may be the predominant group. In my analysis of Lake Kergelen there were nematodes representing ten differ- ent families, of which 50.7% belong to Leptosomatidae (Platonova, 1968). In material also collected from Lake Kergelen, Schuurmans-Stekhoven
Proportion of lower Enoplida in the fauna of nematodes of some seas
Water body Enoplids Enoplids Author Total ————-—— Total —-——-——— Number % Number % Barenieisea 1,040 203. 19 121 26 21 + My data
North Atlantic,
Norway-Green-
land coast — — — 33 9 27 Norway, Trond-
Ditlevsen, 1926
heims Fiord 2,560 182 7 177 6 3.3 Allgen, 1933 Arctic Sea — — — 292 46 15 Allgen, 1957 North Sea — = = 206 11 5 Schuurmans-
Stekhoven, 1935 Baltic Sea, Oresund 3,000 248 8 222 5 2.2 Allgen, 1935 Kiel 3,000 195 7 254 5 1.9 Gerlach, 1958 Mediterranean Sea 614 54 8.7 338 24 7 Schuurmans-
Stekhoven, 1950 Black Sea 5,750 115 2 122 5 4 Platonova, 1962a Tropical part of
Pacific Ocean 970 142 14 109 15 13 Allgen, 1961 Antarctic and sub-
antarctic seas 5,582 546 9.8 343 21 6 Allgen, 1959
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and Mawson (1955) found that leptosomatids constituted 88.0% of the total population of nematodes.
It must be noted that when a ladle with a small catchment area, say 20 to 40 cm? (for example, the standard earthen bowls and other devices for making probes into the meiobenthos) was used for collecting nema- todes, leptosomatids were rarely caught. They were most frequently found in bottom-combing probes where the sweep of the catching device was considerably larger. This fact, which I have noted a number of times, most probably indicates that the average distance between individuals of this group in nature is many times more than in other usually smaller marine nematodes. Possibly this is due to the larger size of leptosomatids (compared to other representatives of the meiobenthos in general and all other nematodes in particular) and also due to their greater mobility.
Hence leptosomatids should be included in the category of organisms of the macrobenthos in spite of their relatively smaller size. A predomi- nant majority of other free-living nematodes are organisms of the meio- benthos, which is supported by their being found in large numbers during standard meiobenthic probes.
Biotopes. All the families examined in the present work are found by and large in all biotopes, from littoral water plants to deep water silt.
Leptosomatids live mainly among larger types of algae with a less fragmented thallus. These are usually brown algae (Fucus, Ascophyllum, Laminaria, Alaria) and rather rarely red algae (Porphyra, Rhodimenia, Halosaccion, Litothamnion, and Corallina). There are numerous nema- todes in these which belong to group IA according to the classification of Wieser (1953). Representatives of this group cannot utilize the algae they inhabit as food material due to the structure of their oral apparatus. Most probably the algae provide them with shelter and mechanical pro- tection against the impact of sea breakers. As is well known, nematodes live in the surface layers of the seabed (Cobb, 1929; Filip’ev, 1934) and for this reason those which live in the zone of sea breakers and the littoral belt need that type of defense.
Wieser (1951) states that smaller forms of nematodes inhabit algae with a highly fragmented thallus (for example Ceramium) and large forms usually inhabit larger algae with a slightly truncated thallus. My obser- vations confirm Wieser’s. Among shrublike and highly dismembered algae I found small forms of Chromadoridae in abundance, but larger leptosomatids (average size 6 to 15 mm) in larger types of brown algae. Group 1B does not include lower Enoplida.
Representatives of group 2A are found in algae of the littoral zone in very significant numbers: some (for example Pseudocella trichodes) may be considered exclusive inhabitants of this biotope. They are capable of utilizing algae not only for shelter but also as food on the basis of their
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oral structure. Group 2B was represented in my material by just six species of two genera—Cylicolaimus and Rhabdodemania. In the littoral zone these nematodes are almost nonexistent. Information in literature on the distribution of other species of these genera support my obser- vations.
Fine sand and gravel are only slightly inhabited by nematodes as these organisms are easily swept away by waves from ground not protected by algae.
Silted sand in the sublittoral zone provides favorable conditions of habitation for nematodes. Here the impact of sea breakers is not felt, food reserves are sufficient, and far better aeration insured compared to silt. As shown by Wieser (1960) the degree of ground siltation exerts a great influence on the development of nematode fauna. Little silt preserves the interstices in which nematodes take refuge. When such spaces are filled by silt, a severe impoverishment of nematode fauna takes place. All three groups—1A, 2A, 2B—are widely represented in this biotope. As men- tioned above, group 2B is found almost exclusively in silted sand beds of the sublittoral zone. Wieser (1951, 1953) believes that species of this group are capable of feeding on small organisms as well as algae, because of the presence of a large and well-armed oral cavity. Proceeding from the fact that species of this group are found very rarely in algae and live mainly in silted sand grounds, one may assume that these nematodes are mainly predators. As far as mollusks are concerned, Filip’ev (1927) and Schuurmans-Stekhoven (1950) think that this biotope always contains a rich fauna of nematodes. But leptosomatids are found among mollusks (lamellibranchs) rather rarely and usually singly. However, Filip’ev (1918) claims he often found species Leptosomatum bacillatum among bivalve mollusks.
Biotopes containing large numbers of invertebrates (independent of their taxonomic groups) are particularly rich in nematodes. Areas rich in polychaetes, mollusks, echinoderms, and sponges are equally rich in nematodes. Probably as a result of the vital functions of these organisms, the substratum is enriched with nutritive material utilized by nematodes.
Temperature. I have no experimental data on the influence of tempe- rature on nematode fauna. Only this observation can be made: Deonto- stoma arcticum, Pseudocella arcticum, P. coecum, and P. trichodes are found predominantly in cold seas of the Arctic basin, while Eusynonchus hirsutus, Leptosomatum bacillatum, and Leptosomatides euxina live in the warm waters of the Black Sea and the Mediterranean Sea. Leptosomatum elongatum may be considered eurythermal as it has been found in the cold waters of the subantarctic, Barents Sea, and Greenland Sea, as well as in the warm waters of tropical parts of the Indian and Pacific Oceans. Data on the remaining species discussed in this work are so meager that
60
at present it is difficult to comment on the influence of temperature on them.
The influence of temperature on nematode fauna is detailed by Gal’t- sova in the present volume (p. 327).
Salinity. Filip’ev (1927), Schuurmans-Stekhoven (1931), and Allgen (1935) observed a reduction in number of free-living marine nematodes in relation to lower salinities. This is clearly evident for nematodes of family Leptosomatidae and Anticomidae. Most species of these families may be considered stenohaline. Fauna comprising leptosomatids and anticomids is much richer with respect to species in seas with a normal oceanic salinity (46 species, see Table). In such seas species of Leptoso- matidae constitute 27% in relation to the total number of nematode species. In seas with lower salinities (Black Sea—17%,, Baltic Sea in region of Gulf of Kiel—13 to 19%,, and considerably diluted waters of Trondheims Fiord, Sea of Norway) the number of species of leptosoma- tids and anticomids falls to 4.0 to 6.0% or 1.9%. In the Sea of Azov (Filip’ev, 1922c; Mordukhai-Boltovskii, 1960) and in the eastern part of the Baltic Sea (Filip’ev, 1929; Schneider, 1906) leptosomatids are entirely absent.
Representatives of Thoracostomatinae (Thoracostoma, Deontostoma, Pseudocella) are probably rather sensitive to lower salinity. Thus in the western part of the Baltic Sea species of these genera are found very rarely and usually singly, while in the Black Sea they are totally absent. The subfamily Leptosomatinae (Leptosomatum, Leptosomatides, Lepto- somella) is usually found in seas with normal salinity. However, two species of Leptosomatum (L. punctatum and L. bacillatum) and Leptoso- matides euxina inhabit the Black Sea.
The family Anticomidae is, as a whole, more euryhaline. Moreover, species of Anticoma, which live in all seas except those with very low sali- nities, are the most euryhaline. Rhabdodemaniidae is adapted to great fluctuations of salinity. In my material there were specimens of Rhabdo- demania from the Okhotsk, Barents, White, and Black Seas. According to Allgen (1929a) and Gerlack (1958) species of the genus are also found in the western part of the Baltic Sea.
The possibility is not ruled out that there may be other factors affect- ing the prevalence of leptosomatid fauna in the Black and Baltic Seas, but indubitably the considerable dilution of water is significant.
The problem of the ecological characteristics of individual species is incomparably more complex. Diversity of habitat and extremely wide distribution of species in various seas and under various conditions (depth, nature of the bottom, and salinity) indicate that many species of this group have adapted to a wide range of ecological factors.
It seems to me that the eurybiont nature of free-living marine nema-
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todes has been rather exaggerated. In my material there were no species encountered in all biotopes in equal measure. Moreover, some species exhibit a distinct affinity for definite conditions. For example, Pseudo- cella trichodes is an inhabitant of large littoral algae, while P. tenius and P. elegans live predominantly in depths of about 300 to 400 m in brown sublittoral silts.
It is difficult to express an opinion on the ecological affinity of species encountered in extremely diverse biotopes. At first sight they appear widely eurybiont and are so regarded by a number of authors (Schulz, 1932; Kreis, 1934; and others). However, it seems to me a careful analysis of the prevalence of these species makes it possible to pinpoint the bio- tope in which a definite species is encountered on a large scale or, at any rate, in a larger percentage than in other biotopes. Such a phenomenon bespeaks, first of all, the affinity of a species for certain conditions; the solitary occurrence of specimens of species in other biotopes can be attri- buted to wider limits of adaptation inherent in free-living nematodes, especially primitive marine forms. Sometimes cases of occurrence of nematodes of a single species in biotopes markedly different from each other can be explained by their drifting with fragments of algae or erosion of beds by sea breakers. Nematodes are also subject to wide-flung dis- persal by currents due to their ability to cling to the surface film of the water. An example of a widely distributed species is Pseudocella kuri- lensis; definite conclusions about its ecological affinity can be derived from its prevalence. This species was found at five places in the littoral zones of Kuril Islands in pieces of algae; however, in all five places only solitary specimens were collected. Contrarily, as many as 49 specimens were found among a dense mass of sponges caught in a probe at 25 m depth on a slightly silted bed. In all probability the latter biotope is favo- rable for the prevalence of this species.
The species Leptosomatides brevisetosum seems to thrive in the littoral zone where it can find shelter in thickets of large algae, although solitary specimens have been recorded from a sandy bottom at a depth of 53 m.
It seems to me that grouping nematodes, as done by Wieser (1953), on the basis of their oral apparatus without taking into account their physiological indexes is incorrect. For example, in my material three species of Pseudocella would fall in group 2A but they apparently thrive under notably different conditions. P. trichodes is an inhabitant of litto- ral algae, while P. tenuis and P. elegans live in sublittoral silts. It is pos- sible that P. trichodes is a more oxygen-loving form than P. tenuis and P. elegans.
The foregoing account shows that in spite of the few studies done to date the ecological characteristics of the family have been sufficiently defined to reveal its primitiveness. For a better understanding of the
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ecology of this group, obviously more field and experimental studies are needed.
GEOGRAPHIC DISTRIBUTION
The geographic distribution of free-living marine nematodes of this group is steeped in confusion and even vacuity.
In the 1920’s and 1930’s many researchers considered free-living marine nematodes cosmopolitan. The hypothesis was put forward that zonal climatic factors play no role in the distribution of nematodes (Steiner, 1915; Kreis, 1934). Chitwood (1936a, 1936b, 1937, 1951, 1960) disputed this point of view on the grounds that species found by him on the coast of America differed significantly from those found on the European coast. Authors of a number of contemporary studies (Gerlach, Mawson, Meyl, Timm, and Wieser) subscribe to this point of view and believe that among free-living marine nematodes there are far fewer cos- mopolitan forms than indicated earlier. Thus Wieser (1953c) found an extremely small number of species of nematodes, common in the fauna studied by him, on the coast of Chile and in coastal waters of Europe. Gerlach (1955) studied the fauna of marine nematodes of the Pacific coast of Central America, and Meyl (1956, 1957) nematodes of the coast of Brazil; they found a large number of new forms not seen in areas studied earlier.
Schuurmans-Stekhoven (1950) in his comprehensive work on nema- todes of the Mediterranean Sea compared this fauna with that of the North, Baltic, Mramor, Black, and Azov Seas. He established that species of nematodes common to the North, Baltic, and Mediterranean Seas do not exceed 15% of all the nematode fauna of the Mediterranean Sea. Contrarily, the Mramor, Black, and Azov Seas have a much larger number of species common to the Mediterranean Sea (34.79%). For the Mramor this figure was 65.0%, the Black 29.5%, and the Azov 33.3%. Thus the fauna of the Mediterranean Sea reveals greater similarity to the fauna of the Mramor, Black, and Azov Seas than that of the more nor- thern seas of Europe. Such an interrelation of the nematode fauna of these seas should be expected if the distribution of these organisms is subject to the same biogeographic phenomena as other groups of marine benthic organisms.
Data presented in a number of works by Allgen (1956a, 1956b, 1956c, 1957a, 1958b, 1958c) are none too clear in this respect. This author compares regions situated great distances apart. Comparing the Norwe- gian nematode fauna with that of other regions he states that at different points of the Norwegian coast significant percentages of species are found which are common to the Mediterranean Sea, tropical seas along
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the coasts of Australia and South America, and also the Antarctic and subantarctic.
In other works (1934a, 1954b) Allgen has stated that several species are bipolar in distribution. All the bipolar species in the northern hemi- sphere live mainly in temperate waters (coast of Norway, England, and France) and in the southern hemisphere in the subantarctic region (islands of Terra del Fuego, Falklands, Campbell, Kergelen, MacCoury, Tasmania, New Zealand) or even in the Antarctic. Thus the distribution of these nematodes is similar to other groups of bipolar organisms. It is interesting that while discussing the reasons for the bipolar distribution of nematodes, Allgen refutes the present theory about the bipolarity of species; their settling in various oceanic depths (Chun, 1897), along the western coasts of continents, particularly in relation to Quaternary gla- ciation (Ortmann, 1896; Berg, 1920), and bipolarity as a result of a uni- formly wide distribution during the Tertiary period (Deryugin, 1915). Allgen holds that bipolar species as well as species known to exist only in one hemisphere are, as a matter of fact, much more widely distributed and their known occurrences are casual and fail to reflect the size of the area of occurrence. Thus in his zoogeographic concepts Allgen reverts to the old opinion that free-living marine nematodes are cosmopolitan forms.
Not negating the possibility of a bipolar distribution of nematodes, I nonetheless hold that for an accurate analysis of this problem a thorough morpho-systematic study of bipolar species is essential. In the works mentioned above Allgen includes two species of Leptosomatidae among bipolar species. The first, Pseudocella elegans, was discovered by Ditlevsen (1922) in the subantarctic but as he had only one specimen, not sexually mature, he gave no description. Ditlevesen later discovered (1926) a large number of sexually mature nemotodes in Skagerrak, which he considered identical to the subantarctic specimen, and gave a de- scription of the species. It seems to me that on the basis of the foregoing account one cannot conclude that this species is bipolar in distribution.
Allgen labeled the second species, Thoracostoma coronatum, bipolar in distribution because he annexed it with Triceratonema campbelli. I cannot accept this contention because the identification of these two forms is erroneous; the former should be considered a Mediterranean form and the latter Antarctic.
Rhabdodemania minor, Leptosomatum arcticum, Deontostoma arcti- cum, and Pseudocella trichodes appear at first glance to be species with a bipolar distribution.
Rhabdodemania minor has been recorded from the coast of Ireland to that of Murmansk and once recorded by Allgen (1959) from the coast of Antarctica. The occurrence of this species in the Antarctic Ocean appears
64
dubious to me as only one female and two immature specimens were recorded, as a result of which identification could have been inaccurate. Specimens of Leptosomatum arcticum were recorded by Filip’ev from the Barents Sea near Murmansk (1916) and near the coast of Novaya Zemlya (1927). Mawson (1958b) found this species in the Antarctic and sub- antarctic. There are sufficient grounds to assume that here the authors were dealing with two different species. The species described by Filip’ev was based on a single female specimen and later a sexually immature specimen found by him near the coast of Novaya Zemlya. A large number of nematodes with mature males and females were at the disposal of Mawson. Having no opportunity to compare the males, on the basis of which a precise species identification is possible, Mawson made a mistake in identification and considered these two different species one.
The bipolar distribution of Deontostoma arcticum appears more valid. This species is often found in the lower Arctic and in boreal waters. It has occurred in large numbers along the southern coast of Chile (Wieser, 1953c) and in the Antarctic and subantarctic (Mawson, 1956, 1958b). Pseudocella trichodes is a species widely distributed in the littoral zone in Arctic and boreal waters, living mainly among larger algae. Allgen (1951, 1959) indicates the occurrence of this species on the south coast of Australia (one sexually immature specimen) and in the subantarctic in the sandy and silted-sand benthos of the sublittoral zone. Leptosomatum gracile and Synonchus fasciculatus have been recovered from the North Atlantic and Arctic Oceans. They were also detected by Allgen in the subantarctic region.
Thus the problem of the bipolarity of distribution of marine nema- todes requires, in my opinion, a special exhaustive study.
If the distribution of marine nematodes is mainly subject to the same zoogeographic laws as the distribution of all other groups of marine benthic organisms, then one may essay, albeit in general outlines only, a zoogeographic classification of species and isolate groups of species characteristic for different seas. It should be noted beforehand, however, that specialists of other groups of marine benthos deal with organisms for which the zoogeographic characteristics are fairly clear. For marine nematodes this problem is still in the process of elucidation. To explain this phenomenon I want only to show the potentiality of a zoogeographic analysis of distribution of lower Enoplida. Marine nematodes in general have been studied too little to permit an exhaustive review. With the manifestation of affinity (adaptation) of an individual species to one or another zoogeographic entity, one can be guided by the scheme of zona- tion of the seas (to be exact, sublittoral) proposed by Ekman (1935, 1953), which is universally recognized.
Odontanticoma murmanica, Anticoma insulaealbae, Leptosomatum
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tetrophtalmum, Leptosomatides steineri, Pseudocella tenuis, and P. coecum are known from numerous points only in the Kara and Barents Seas. On the basis of their type of distribution they can probably be consi- dered Arctic species. Other Arctic species include Deontostoma magni- ficum and Ritenbenkia micropapillata, and species described earlier in this work—Anticoma filipjevi, A. grandis, and Pseudocella gracilis. But since these species were only found singly, it is difficult to make a statement about their distribution.
Anticoma arcticum A. minor, Rhabdodemania minor, R. gracilis, R. scandinavia and Synonchus murmanicus should probably be considered arctico-boreal species, because of their occurrence in the Kara and Barents Seas as well as in the boreal waters of Europe (North Sea and coast of England).
I cannot assign a number of species to a definite group because they constitute solitary specimens. However, as their habitats are widely dis- persed in the Kara, Barents, and Norwegian Seas, the North Atlantic, and the North Sea, it may be that the following species will eventually be regarded as arctic, arctico-boreal, or less probably boreal species: Anticoma strandi, A. brevisetosa, Odontanticoma vanoorti, Crenopharynx armatus, Barbonema setifera, Platycomopsis cobbi, P. mesjatzevi, Lepto- somatides microlaimum, L. crassus, Leptosomatum arcticum, L. groen- landicum, L. breviceps, Leptosomella acrocerca, Pseudocella conicaudata, P. saveljevi, P. filipjevi, and Deontostoma lobatum. There is an analogous collection of species known to occur only singly from the Bering Strait, Commander Islands, and the northern part of the Sea of Azov: Anticoma behringiana, A. curta, A. uschakovi, Rhabdodemania ochotensis, R. brevicaudata, Leptosomatum papillatum, L. grebnickii, L. behringicum, Pseudocella acuta, P. angusticeps, and Deontostoma papillatum. Like the species in the previous list, they are also arctico-boreal or upper boreal. However, at present it is not possible to define their biogeographic characters.
Anticoma eberthi, A. limalis, Crenopharynx marioni, Rhabdodemania laticauda, Leptosomatum gracile, Metacylicolaimus filicaudatus, M. obtusidens, M. flagellicaudatus, M. effilatus, and Fiacra longisetosa may be considered boreal-European forms distributed along the coasts of Norway, in the North and Baltic Seas, and along the coasts of England and France. From the records of solitary specimens it is possible that the following species may belong to this group: Anticoma zosterae, A. microseta, Barbonema horridum, Rhabdodemania striata, R. major, Platy- comopsis effilatus, Leptosomatum caecum, Jaegerskioeldia acuticaudata, and Eusynonchus brevisetosus.
Species found by me near South Sakhalin and Kuril Islands may apparently be considered boreal or even lower boreal-Pacific forms:
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Odontanticoma dentifer, Leptosomatum acutipapillosum, L. brevisetosum, Anivanema magna, Pseudocella bursata, P. kurilensis, P. mamillifera, and P. truncaticauda. Probably Rhabdodemania illgi from the Pacific coast of North America, known only from one habitat, could be transferred to this group.
A significant number of anticomids and leptocomids live in the Mediterranean Sea. Frequently found species include: Anticoma pellu- cida, Platycoma cephalata, Crenopharynx paralepturus, Leptosomatum punctatum, L. bacillatum, Anivanema magna, Cylicolaimus (?) jaegerskio- eldi, Eusynonchus hirsutus, Tuerkiana strasseni, Paratuerkiana comes, Deontostoma montredonense, Thoracostoma coronatum, and T. zolae.
Anticoma tyrrhenica, Crenopharynx metagracilis, C. brevicaudatus, Pseudocella cavernicola, and P. citronicauda have been recorded as isolat- ed cases from the Mediterranean Sea. It is important to note that some of the species go beyond the limits of the Mediterranean Sea and are dis- tributed in the north up to the coast of England, while others are not known beyond the limits of this sea.
From the Black Sea only five species have been recorded: Anticoma pontica, Leptosomatides euxina, Rhabdodemania pontica, Leptosomatum punctatum and L. bacillatum. Of these, the first three have been dis- covered only in the Black Sea to date.
In the Indo-West Pacific (Southeast Asia: Malayan Archipelago and along the Indian coast) single finds have been recorded for these species: Anticoma ditlevseni, A. aberrans, A. procera, A. profunda, Anticomopsis filicauda, A. tenuicollis, Paranticoma elegans, P. bandaensis, P. profunda, Platycomopsis filiappendicatus, Leptosomatum ranjhai, L. keiense, Lepto- somatides reducta, Leptosomatina longisetum, Thoracostoma philippin- ensis, and T. karachense. To date these species have not been discovered outside the limits of this region.
Steiner and Albin (1933) and Allgen (1951) recorded the following species of anticomids and leptosomatids along the Pacific coast of Cen- tral America: Anticomopsis tenuis, Leptosomatum pedroense, Deontostoma microlobatum, D. anchorilobatum, D. jollaensis, D. californicum, and Pseudocella panamaense. Only isolated specimens were found, however.
Anticomids and leptosomatids are particularly numerous in the Antarctic and subantarctic. Species repeatedly encountered include: Anticoma longissima, A. dahli, A. tenuis, A. filicauda, A. subsimilis, A. major, A. columbia, A. campbelli, A. australis, A. wieseri, Paranticoma antarctica, Crenopharynx antarcticus, Platycomopsis dimorphica, Deonto- soma auclandiae, D. antarcticum, Thoracostoma anocellatum, T. vallini, T. angustifissulatum, T. campbelli, T. setosum, T. australe, Pseudocella brachychaites, P. tabarini, and P. polychaetes. Species found only once: Anticoma lata, A. kerguelensis, A. extensa, A. longisetosa, A. graciliceps,
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Paranticoma odhneri, P. tubuliphora, Anticomopsis gibbonensis, Creno- pharynx serialis, C. crassus, Rhabdodemania calicolaimus, Platycomopsis paracobbi, Leptosomatum australe, L. crassicutis, L. kerguelense, L. clava- tum, Leptosomatides conisetosum, Deontostoma papillosum, D. demani, Thoracostoma chilensis, T. schizoepistylium, T. parasetosum, and T. brunni. The study of marine nematodes is too inadequate to permit a statement as to which species are exclusively adapted to the subantarctic and which to the Antarctic. However, it may be noted that most of these species are known from both the subantarctic and the Antarctic.
The distribution of four species of Anticoma has given rise to doubts. Anticoma pellucida is widely distributed in the Mediterranean Sea. It has also been detected in the North Sea and the North Atlantic as far as the Barents Sea. Allgen (1927b) recorded this species for the subantarctic. A. acuminata has also been mainly found in the Mediterranean Sea and adjacent seas; it has also been recorded from Zond Islands (Micoletzky, 1930), the Pacific coast of North America (Wieser, 1959), and in Antarc- tic and subantarctic waters (Allgen, 1959). A. limalis is often found in the Arctic, North Atlantic, North Sea, and the western part of the Baltic Sea. Allgen recorded this species near the coast of California (1947b), for the Pacific and Atlantic coasts of Central America (1947a, 1951), the Caribbean Sea, the Philippines, the Hawaiian Islands, and the Antarctic and subantarctic (1959). A. similis has been recorded from the coast of Australia, Terra del Fuego, in the subantarctic, Antarctic, and Zond Islands. Probably these four species could have been classed as cosmo- politan had their taxonomic status not undergone so much confusion. As is mentioned in the taxonomic part of this work, some were combined repeatedly into one species and then separated subsequently. The limits of these species have not yet been distinctly defined. Hence the problem of their distribution must remain open.
Three species of Leptosomatum also appear at first glance to be cosmo- politan in distribution. L. bacillatum is widely distributed in the Mediter- ranean and adjacent seas and has also been recorded from the Norwegian and Caribbean Seas, on the coast of California and South Australia, and in the subantarctic and Antarctic. However, Allgen (1940a, 1943, 1947, 1951, 1959) had insufficient material at his disposal: most of it comprised females and sexually immature specimens. For this reason I am inclined to consider L. bacillatum a Mediterranean species. L. sabangense was first recorded from the islands of Zond by Steiner (1915). Later this author mentions the discovery of this species along the coast of Venezuela; as only a single sexually immature specimen was found I fear his identifica- tion may have been erroneous. Micoletzky recorded this species from the Red Sea (1922) and Allgen from the Mediterranean Sea, the coast of California, Panama (along the Pacific coast), Australia, and the Falkland
68
Islands. In every instance only one to three specimens were recovered and these too were sexually immature. For this reason I consider it an Indo-West-Pacific species. L. elongatum is widely distributed in the arctic and boreal regions. It has been found in the Mediterranean Sea, in the tropical part of the Indian Ocean, in the Pacific Ocean, on the coast of Panama and California, on the western coast of Australia, in the suban- tarctic and Antarctic.
It is extremely difficult to determine the geographic distribution of some species. Anticoma ditlevseni was first recorded by Micoletzky near the islands of Zond (233 specimens). Most of the specimens were sexually mature. Allgen has recorded the occurrence of one female of this species from the coast of Norway. Anticomopsis typicus was also recorded for the first time by Micoletzky near the islands of Zond. Luc and de Coninck (1959) discovered a male and female of this species in LaManshe. Wieser (1953c) recorded Pseudocella kreisi for the first time on the coast of Chile (one specimen which was sexually immature). Later (1956), he found one male off Sri Lanka (Ceylon) at a depth of 3,400 m. Thoraco- stoma steineri was described by Micoletzky (1922) on the basis of one female specimen found in the Red Sea. Later (1930) he found a signi- ficant number of sexually mature specimens of this species on the islands of Zond. Allgen found this species in the Mediterranean Sea and on the coast of California. Schuurmans-Stekhoven (1943, 1950) also discovered it in the Mediterranean Sea but his description differs significantly from that given by Micoletzky.
The material presented, it seems to me, bears testimony to the fact that free-living marine nematodes are not universally (ubiquitously) distributed organisms. Each zoogeographic region corresponds strictly to a well-defined group of species. Most of the data about the extremely wide distribution of species reflects an inadequate study of their system- atics.
Studies of the zoogeographic characteristics of genera of lower en- oplids are almost impossible today. All the genera, irrespective of species composition, are transoceanic and only some, mainly monotypic ones, have an affinity for definite regions.
In conclusion, it must be stated that the main problem in the analysis of the geographic distribution of nematodes is inadequate study of their fauna in most regions of the world. An accumulation of faunistic infor- mation in the future should significantly elucidate their zoogeographic analysis.
COLLECTION AND PROCESSING OF NEMATODES
Collecting nematodes is a very simple but laborious process. Infor- mation on this procedure is available in the works of Filip’ev (1926b) and
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Goodey (1959). In the littoral zone samples are collected manually from the benthos and algae at rather shallow depths with the help of dredges operated from a boat. In the sublittoral zone benthos is scooped up by standard equipment used for such purposes, i.e., various types of trawls and dredges. Extracting nematodes from the seabed is not so easy. The method of “‘thorough-wash”’ is preferable for obtaining nematodes in a more concentrated mass. In this method the probe situated in Koch’s cup is shaken vigorously and the contents poured into another container. Only larger, coarse particles of the benthos remain at the bottom of Koch’s cup. This operation is repeated several times. The poured-off water contains nematodes and fine particles of benthos. It is filtered through a sieve with a fine mesh (No. 69) to remove the fine particles of silt. The benthos remaining on the sieve and containing a large number of nematodes is examined under a binocular microscope in Bogorov’s chamber. Worms thus isolated are preserved in 70° alcohol or 4% formalin.
When nematodes are collected from algae the latter is shredded and separated in a large glass container. The material is then filtered through a sieve of large mesh to separate the algal fragments. The filtrate, con- taining small fragments of algae and nematodes, is subsequently passed through a sieve of fine mesh (No. 69). The remaining mass is either pre- served as a whole or subjected to selection; nematodes freed from foreign particles and floating in clean water are preserved.
To make preparations of nematodes the worms are transferred from the preservation medium to a mixture of equal volumes of 96° alcohol, distilled water, and glycerine, and kept there for 3 to 12 days depending on the size and transparency of the nematodes. In this mixture the nema- todes become transparent, after which they are transferred to pure glycerine for 12 to 20 hours. Nematodes processed in this manner are mounted in a glycerine-gelatin medium.
Systematics
Certain clarifications are necessary before proceeding with the taxo- nomic classification of Enoplida. First of all, the order Enoplida is divided into two superfamilies—Enoploidea and Leptosomatoidea. A characterization of each superfamily is presented, followed by a key to families which, in addition to serving the purpose of identification, gives some idea about the size of each superfamily. This information is essen- tial to my later detailed discussion of the four families—two from each superfamily.
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Species earlier assigned to just family Leptosomatidae and recorded from marine bodies of the Soviet Union are described herein and re- distributed in four families—Leptosomatidae, Anticomidae, Rhabdo- demaniidae, and Crenopharingidae. Species present in my material are not only described but depicted in original illustrations. All the measure- ments of body parts are based on my own material. For species not represented in my material but described by other authors from these seas, I have presented the published descriptions which, because they vary in style, could not be fitted into the scheme adoped for describing species at my disposal. Descriptions taken from literature are asterisked. Species encountered in the seas of the Soviet Union are numbered in the keys.
1. Order ENOPLIDA Schuurmans-Stekhoven and Coninck, 1933
Free-living nematodes of rather large size, complete in organization, and subject to less reduction (Filip’ev 1918, p. 37). Characters: cuticle almost always smooth, but nematodes of the family Lauratonematidae with annulations constitute an exception. Oral opening encircled by six papillae (occasionally setae); another circle, consisting of ten papillae, or two circles, one consisting of six and the other of four setae (occasionally papillae) situated on head. Occasionally setae of first circle totally reduc- ed. Amphids cyathiform with transverse slit either elliptical or longitudi- nally elongated. Esophagus almost cylindrical, sometimes gradually broadening toward base. Esophageal glands often open sublaterally in lower part of oral cavity. Esophagi characteristic of the order either fuse with the cuticle anteriorly or show signs of an earlier attachment, disap- pearing subsequently due to powerful development of the oral cavity. Oral cavity later loses its capacity to extrude due to weak development and differentiation of muscles of anterior end of esophagus. Structure of oral cavity highly variable. Genital tubes mostly paired; family Laurato- nematidae exceptional in which females have reproductive tubes with a reduced posterior part.
Key to Super families of Order Enoplida
56 1 (2). Esophagus with wavy margin in posterior part, rarely cylindrical. Oral cavity sharply divided into two parts: buccal cavity with jaws or buccal stylets or simply lined with sclerotized cuticle, and onchial cavity often armed with onchia. Esophageal musculature extends anteriorly only up to anterior margin of onchial cavity..........
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= CaS ULERY ESM Pg Reve oR 2. Enoploidea Baird, 1853. 2 (1). Esophagus cylindrical and without wavy margin. Oral cavity either not expressed or without sharp division into buccal and onchial parts. Onchia, if present, displaced toward oral opening due to protrusibility of oral musculature almost up to oral opening...... gene rae Sc Males eA SNS A er 1. Leptosomatoidea Filipjev, 1918.
1. Superfamily LEPTOSOMATOIDEA Filipjev, 1918
Sclerotized cephalic capsule well developed in many representatives. Oral cavity either completely reduced or with a simple structure and not divided into buccal and onchial parts. Additionally, its armature never represented by jaws or buccal stylets. Of the derivatives of the buccal cavity, only development of odontia (Cylicolaimus for example) possible. More often in forms with oral armature, odontia represented by onchia (derivatives of onchial cavity), which are notably shifted toward oral opening due to protrusibility of esophageal musculature. Esophagus widens gradually from anterior end toward base; alveolate structure never observed in posterior half. Cuticle covering the body thick, smooth, and often with fascicles of intersecting fibers in external layer. Amphids in most forms round or cyathiform. Some representatives of Oxystominidae have extremely narrow, and longitudinally elongated amphids.
Key to Families of Superfamily Leptosomatoidea
1 (8). Cephalic setae (10 in number) situated in single circle. Amphids usually cyathiform.
2 (7). Cephalic capsule either poorly or well developed; oral cavity cyathi- form, sometimes extremely short or not developed at all.
3 (4). Cephalic capsule very poorly developed; oral cavity armed with thireconchiai waichiresemble mandibles 7455 34)32)) 0.35 acle... as sll le eae eB Me a es a a Triodontolaimidae de Coninck, 1965. REE Ves oe al [Only species: Triodontolaimus acutus (Villot, 1875)].
4 (3). Oral cavity unarmed or its armature represented by typical onchia.
5 (6). Cephalic capsule either absent or so poorly developed as to be undetectable. Body tapers distinctly toward both ends.......... Bini Bieta Ie coat Phn 31 TES a eran RS 2. Anticomidae Filipjev, 1918.
6 (5). Cephalic capsule always present and represented by powerful sclerotized structure in a number of forms. Body tapers slightly toward anterior end but negligibly toward posterior end........ Bey stele ree ce unis eduyesi olay eo mg 1. Leptosomatidae Filipjev, 1916.
7 (2). Cephalic capsule absent; oral cavity in the shape of a long, narrow CYLMA SRA eee eee PLR ee UNE RE Ironidae de Man, 1876.
Si
q2
8 (1). Cephalic setae situated in two circles (six plus four); some setae reduced in some forms. Amphids with large openings, sometimes highly elongated in longitudinal direction.................... » REESE, DRE, Pesakcaes Oxystominidae Micoletzki, 1924.
1. Family LEPTOSOMATIDAE Filipjev, 1916
Large free-living marine nematodes, ranging from 10 to 50 mm in length. Cuticle thick, often multilayered. Ten cephalic setae always arranged in one circle. Mouth encircled by six papillae. Some genera with eyes or spots of photosensitive pigment. Esophagus straight, without bulbs. Cardia large, triangular. Most characteristic features of family: presence of sclerotized cephalic capsule with various degrees of com- plexity evident in endocuticle. More or less developed oral cavity armed with onchia or odontia in a number of forms. Gonads always paired and no sign of their reduction ever observed. Females with paired gonads, genital ducts, and uteri. Only testes paired in males, which later merge into an unpaired vas deferens and ejaculatory duct. Spicular apparatus of males highly diverse in structure but always consists of a pair of spi- cules and a gubernaculum. Gubernaculum with paired or unpaired processes. Most species of this family have an accessory organ, anal setae, and papillae. Caudal glands three, tubular or fusiform, and almost always open terminally at the tip of the tail.
Key to Subfamilies of Family Leptosomatidae
1 (4). Cephalic capsule highly developed, thick-walled.
2 (3). Interlobular grooves of cephalic capsule differentiated into narrow furrows and wide fenestrae; lateral grooves differ in shape from the rest.< Lailyshontsand)bluntly:rounded:, 722% .2 3055.3: ee eee eee sep Ne Belch sk on abla an eAean SR Sion en ed coe 3. Thoracostominae de Coninck, 1965.
3 (2). Interlobular grooves of cephalic capsule not differentiated and uni- form in shape. Tail elongated and claviform.................. BG, DASE Te OPE Ay 2. Synonchinae Platonova, 1970.
4 (1). Cephalic capsule poorly developed, thin-walled.
5 (6). Oral cavity highly developed, thick-walled, and armed with onchia. LOU. BARR AAIR Be Sacco a cna Cylicolaiminae Platonova, 1970.
6 (5). Oral cavity not developed...... 1. Leptosomatinae Filipjev, 1916.
1. Subfamily LEPTOSOMATINAE Filipjev, 1916
Nematodes with poorly developed, short cephalic capsule. Cephalic suture straight or slightly wavy and without interlobular grooves. Lepto-
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somatides conisetosum, with a cephalic suture with a deep groove, consti- tutes an exception.! Amphids always situated below line of cephalic suture. Cephalic ring narrow. Oral cavity poorly developed, almost absent. Esophagus encircled by nerve ring between anterior third and fourth part. Sclerotized granules sometimes present around the vulval slit on cuticular surface. Tail short and bluntly rounded in most repre- sentatives of family. Cephalic and preneural setae extremely short; latter sometimes absent. Posterior body end in males may or may not be armed with setae. Well-developed photosensitive eyes present in most BDuCec a tatives of subfamily.
Key to Genera of Subfamily Leptosomatinae
W@)sMailiclavifOrm ys .cio% oS vaste cps 3. Leptosomelia BipIeN: 1927. 2 (1). Tail conical, rounded, or acicular. 3 (6). Eyes present. 4(5). Gubernaculum small, without processes................-.++.- EP eth tes sett tee ote ants ls 2 1. Leptosomatum Bastian, 1865. 5 (4). Gubernaculum large, with large dorsal process..............-- BO cites “arepibiane uemydays ah we bene 2. Leptosomatides Filipjev, 1918. 6 (3). Eyes absent. 7 (8). Spicules with velum. Gubernaculum with ventral and dorsal pro- CESSES etch ities c. sibyeyay es cleus as Paraleptosomatides Mawson, 1956. (Two species: P. spiralis Mawson, 1956 and P. elongatus Mawson, 1956.) 8 (7). Spicules without velum. Gubernaculum with dorsal process only. mn: Rs erat des pashagy «si raraegies BGangy ster Leptosomatina Allgen, 1951. (Two species: L. longisetum Allgen, 1951 and L. appendixocaudatum Allgen, 1957.)
1. Genus Leptosomatum Bastian, 1865
Bastian, 1865: 144; Eberth, 1863: 18 (Phanoglene non Nordmann, 1841); de Man, 1893; 102; Filip’ev, 1961: 65; 1918: 42.
Type species. L. elongatum Bastian, 1865.
Nematodes of large size. Body tapers slightly toward anterior end and almost not at all posteriorly. Head slightly truncated. Cephalic cap- sule, though poorly developed, with walls which may vary significantly in width. Cephalic ring varies in position within limits of upper half of
1It is possible that this species will be transferred in the future to another genus or even to another subfamily. Having no material at my disposal, I could not solve this problem just now.
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cephalic capsule. Labial papillae distinct. Cephalic setae similar to pre- anal setae but occasionally rudimentary with appearance of small papil- lae. Anal setae absent. Amphids circular. Oral cavity poorly developed. Esophagus immediately apposed to oral opening. Lips and anterior part of esophageal wall often sclerotized and thickened. Vulva situated mid- body. Spicules simple in structure and slightly arcuate; in some species only proximal part curves sharply. Gubernaculum small and simple in structure. Most species with preanal glands but no distinct accessory organ on outlet on wall surface. Accessory organ well developed only in L. keiense and L. ranjhai; preanal papilla also present in latter species.
In the description of species of both Leptosomatum and Leptosoma- tides figures in Cobb’s formula indicate the distances of the following parts of the body from the anterior end: 1. posterior end of cephalic capsule; 2. pigmented eyes; 3. nerve ring; 4. base of esophagus; 5. com- mencement of anterior genital tube; 6. vulva; 7. commencement of pos- terior genital tube; and 8. anus.
For the male the first four measurements are those given for the female. The dash which follows indicates the middle of the male body. The last figure indicates the distance from the anterior end to the anus. The corresponding width of the body is given below the line for those parts of the body described above.
Key to Species of Genus Leptosomatum
1 (38). Photosensitive eyes in preneural region. 2 (37). One pair of photosensitive eyes present, consisting of pigment bowl and light-refracting lens. 3 ( 4). Cephalic capsule very short; width exceeds length six times.... THEE ORTH SUS CLL Se AM a mar aT en ET 8. L. breviceps Platonova, 1967. 4( 3). Cephalic capsule significantly longer; ve exceeds length by not more than three times. 5 (12). Cephalic setae well developed. 6( 7). Head highly flattened.............. L. australe Linstow, 1906. 7( 6). Head anteriorly rounded. 8( 9). Amphids situated from anterior end at a distance equal to 3.5 times the cephalic diameter........ L. Micoletzky Inglis, 1971. 9( 8). Amphids situated from anterior end at a distance equal to 1.0 to 1.5 times the cephalic diameter. 10 (11). Width of amphids equal to one-third corresponding body width. NA See Hides etic yy rae Hie .....6. L. punctatum (Eberth, 1863). 11 (10). Width of amphids equal to one-fourth corresponding body WAGE ee oar We hoe EUAN L. keiense Micoletzky, 1930.
12( 5).
13 (18). 14 (15).
15 (14). 16 (17).
17 (16).
18 (13). 19 (26).
20 (21).
21 (20). 22 (23).
23 (22). 24 (25). 25 (24). 26 (19). 27 (28).
28 (27). 29 (30).
30 (29). 31 (34).
32 (33). 33 (32). 34 (31). 35 (36).
60 36 (35).
37( 2).
75
Cephalic setae either rudimentary, resembling papillae, or more often absent.
Males with accessory organ.
Cuticular rays present on cephalic capsule.................. yee Hot GR cl ety a He EU L. ranjhai Timm, 1960. Cuticular rays absent on cephalic capsule.
Lens-shaped broadening occurs in anterior part of esophagus. PUTA CASK Ane HUM BER ae a 4. L. bacillatum (Eberth, 1863). Lens-shaped broadening does not occur in anterior part of eso- fo) see sR MT pes fy as 4 eat ALE ts cS A 9. L. gracile Bastian, 1865. Males without accessory organ.
Cephalic setae rudimentary and do not project on surface of cuticle.
Cephalic setae pierce cuticle and form a coronet on cephalic CAMSUIEM sais oe saci ers eure Ue L. crassicutis Platonova, 1958. Coronet on cephalic capsule absent.
Head broadens and appears clavate in region of cephalic setae. . STR eg tian lah ae ad da oe vee ac an che L. clavatum Platonova, 1958. Broadening of head in cephalic region not evident.
Amphids cordate............ L. kerguelense Platonova, 1958. Amphids) transversely oval in)shapes . 628.) ese eo es isis) AEC Cd AUG RC ALAS APP GN Dara et Ea L. sabangense iiemee 1915).
Cephalic setae short but nonetheless project on cuticular surface.
Tail extremely short; length does not exceed three-fourths of anal idiameter.) Yee Jewel ae L. pedroense Allgen, 1947. Tail length exceeds anal diameter.
Body diameter near eyes equal to 2.5 times cephalic diameter. . PAA ORES SME Met ccna art 3. L. behringicum Filipjev, 1916. Body diameter equal to twice cephalic diameter.
Eyes situated at a distance twice cephalic diameter from anterior end.
Lateral organs equal to one-sixth cephalic diameter from ante- 1a oyen(=)0Val ey Namen an Mees Geena 2. L. grebnickii Filipjev, 1916. Lateral organs equal to one-tenth cephalic diameter from ante- ION Ais Ma es eho hl 1. L. arcticum Filipjev, 1916. Eyes situated at a distance thrice cephalic diameter from anterior end.
Spicular capitulum demarcated from body of spicule by a dis- tinct necklike constriction...... 5. L. elongatum Bastian, 1865. Spicules with no necklike constriction..................00-. TREAD EAU einai ReatisIRY Stag eg ¢ L. acephalatum Chitwood, 1936. Two pairs of photosensitive eyes present; on pair consists of pig-
6
=
76
ment bowl and light-refracting lens and second pair simple col- lection ofepiomicnts ase 7. L. tetrophtalmum Saveljev, 1912.
38( 1). Photosensitive eyes absent.
39 (40). Cephalic setae extremely long; length equal to one-half cephalic diameter erry WA ree See ae L. caecum Ditlevsen, 1923.
40 (39). Cephalic setae short.
41 (42). Esophagus granulated in anterior part...................... SR NBN ah OU Sees ea L. bathibium Allgen, 1947.
42 (41). Esophagus not granulated.
43 (44). Width of amphid one-sixteenth corresponding cephalic diameter. SPE eR Se SAA Aeon L. abissale Allgen, 1915.
44 (43). Width of amphid one- hind corresponding cephalic diameter. . Bais Mc ae ce ctaleig eben acne eenae L. groenlandicum Allgen, 1954.
1. Leptosomatum arcticum Filipjev, 1916 (Figure 14) Filip’ev, 1916: 66-68, tab IV, fig. 1; Mawson 1958b: 315, fig. la-c.
19: 20 120 335 1,275 6,200 7,550 9,100 10,725 52 73 140 170 — 210 — 150 b—=9:'c—o2; V —697
10,900 um; a= 52;
Body elongated, fairly thick, and tapers to almost 1/4 midbody diameter at anterior end and to 5/7 midbody diameter at posterior end. Width of cephalic capsule 2.6 its length. Cephalic ring situated midlength of cephalic capsule. Cephalic suture slightly sinuous. Labial papillae rather short. Cephalic setae, like cervical ones, extremely short; length does not exceed 4.0 wm (1/13 corresponding diameter). Amphids 7.0 um in diameter and situated 30 wm from anterior end (1/40 esophageal length). Eyes situated 120 wm from anterior end (1/10 esophageal length). Size of pigment bowl 5.0 wm x 9.0 um; diameter of lens 7.0 wm. Esopha- geal wall near mouth highly sclerotized. Esophagus thin and widens slightly in posterior part. Nerve ring situated 335 wm from anterior end (approximately 1/4 esophageal length). Vagina thick-walled. Sclerotized granules scattered on cuticle around vulva. Genital tubes not detected.
Filip’ev, who described the species, mentions the following characters which distinguish it from other species: 1) L. elongatum—small size, small amphids, and better developed cephalic capsule;.2) L. bacillatum—twice larger but has smaller amphids and eyes; 3) L. terrophtalmum—absence of additional pair of eyes situated behind original eyes and more sub- median position of vulva; 4) L. grebnickii—structure of cephalic capsule and much larger amphids; 5) L. behringicum—significantly better devel- oped cephalic capsule, much larger amphids, and eyes and setal armature slightly reduced.
60
fy)
= i
Figure 14. Leptosomatum arcticum.2
Geographic distribution. Barents Sea (littoral and sublittoral zones up to a depth of 5.0 m, among Lithothamnion sp. and Laminaria sp.). Occur- rence in subantarctic (Mawson, 1958b) dubious.
2. Leptosomatum grebnickii Filipjev, 1916 (Figure 15) Filip’ev, 1916: 68-70, tab. IV, fig. 2.
Holotype 9: Zoological Institute, Academy of Sciences, USSR. Col- lection nos. 5778, 5779. 15 80 356 1,385 5,200 7,750 11,500 11,910 60 100 107 124 — 185 — 120 c=92; V=64%.
Body large and tapers to 1/5 midbody diameter at anterior end and to 5/7 midbody diameter at posterior end. Caudal length equal to width. Cuticle 7.0 wm thick, with fascicles of intersecting fibers. Cephalic cap- sule better developed than in L. arcticum; width 2.2 length. Cephalic ring situated in middle of cephalic capsule and narrower than in L. arcticum. Cephalic suture barely visible. Labial papillae larger and wider than in L. arcticum. Cephalic and cervical setae short, 5.0 wm (1/12 correspond- ing diameter). Amphids situated 30 wm from anterior end (1/4 esophageal
12,040 wm; a=65; b=9;
2Scale for Figures 14 to 86 corresponds to 50 um.
62
78
length); diameter of amphids 9.0 ym (1/6 corresponding body diameter). Eyes 80 wm from anterior end (1/17 esophageal length). Pigment bowl 8.0 wm x 12.0 wm; diameter of lens 9.0 wm. Esophageal wall near oral opening greatly thickened. Nerve ring at a distance of 365 wm from ante- rior end (1/4 length of esophagus). Esophagus long, narrow, and widens slightly toward posterior end. Sclerotized granules scattered around vulva on cuticle. Genital tubes not detected.
YI
Very close to L. arcticum in structure, but differs from latter in wider, shorter, and significantly less sclerotized cephalic capsule; significantly narrower cephalic ring; and much larger amphids.
Geographic distribution. Barents Sea.
—
| i
Figure 15. Leptosomatum grebnickii.
_ — —_—
3. Leptosomatum behringicum Filipjev, 1916 (Figure 16)
Filip’ev, 1916: 70-72.
Holotype 9: Zoological Institute, Academy of Sciences, USSR. Col- lection nos. 5780, 5781.
80 82 295 1,100 2,650 5,300 8,700 9,673 50 100115 145 — 170 ~— _— 80 c= 126; V=56%.
Body tapers to 5/28 midbody diameter at anterior end and to 1/2 midbody diameter at posterior end. Tail extremely short; length almost equal to width in anal region. Cuticle 4.0 wm thick, with fascicles of in- tersecting fibers. Cephalic capsule extremely short and wide; width exceeds length by 3.7 times. Cephalic ring very narrow and situated in upper part of cephalic capsule. Cephalic suture slightly sinuous. Labial papillae extremely minute. Cephalic setae also short, 2.0 wm long (1/25
9,750 um; a=57; b=9;
719
corresponding diameter). Cervical setae not detected. Amphids situated 25 wm from anterior end (1/40 esophageal length). Diameter of amphids 5.0 um (1/9 corresponding body diameter). Eyes situated 82 wm from anterior end of body (1/13 esophageal length). Pigment bowl small, only 5.0 wm x 8.0 wm; diameter of lens 5.0 wm. Esophageal wall sclerotized in oral region. Esophagus slender and broadens slightly in posterior part. Nerve ring situated 295 wm from anterior end (1/4 esophageal length). Vulva situated midbody. Eggs spherical and 150 to 160 ym in diameter. Genital tubes not detected.
oe eee
Figure 16. Leptosomatum behringicum.
Structurally close to L. grebnickii but distinguished from it in: 1) more weakly developed labial papillae; 2) more weakly developed seta- ceous armature; 3) position of cephalic ring situated in upper part of cephalic capsule in present species; 4) smaller size of amphids; and 5) smaller size of-eyes.
Geographic distribution. Barents Sea.
4, Leptosomatum bacillatum (Eberth, 1863) (Figure 17)
Eberth, 1863: 19, 20, tab. II, figs. 1 to 4 (Phanoglene); Bastian, 1865: 146; Marion, 1870: 17, 18, pl. C., fig. 2 (Stenolaimus macrosoma); de Man, 1876: 103, tab. 8, fig. 9a, b: Filip’ev, 1918: 44-48, tab. 1, fig. 1; Allgen, 1940a: 488, Fig. la, b; Schuurmans—Stekhoven, 1950: 25-28, fig. la, b.
11-13 73-75 280-285 1,090-1,110 — 9,207-9,260
23:39 50-57 80-82 952100120 80-82 00 -93°> pm; a=78-79; b=8-9; c=98-—100. 15 9; Qr12 75-80 235-240 1,030-1,045 4,050-4,200_5,200-5,350
° 27-30 55-60 70-80 95-100 — 120
63
80
x —_ 08S 8,600-8,700 ym; a=69-74; b=8-9;
e=110-145; V=60%.
Body tapers to 1/4 midbody diameter at anterior end and 2/3 at post- erior end. Head rounded. Tail length almost equal to width. Cuticle bilay- ered and 5.0 to 6.0 wm thick; thickness of exterior layer 1.0 wm. Fascicles of intersecting fibers extend into outer layer of cuticle. Cephalic capsule thick-walled; width three times length. Cephalic ring situated in upper- most part of cephalic capsule. Cephalic suture and labial papillae barely discernible. Cephalic and cervical setae extremely small, not exceeding 1.5 wm (1/20 corresponding diameter). Amphids situated 18 to 25 wm from anterior end (1/50 esophageal length) and 8.9 wm x 7.5 um (1/4 to 1/5 corresponding body diameter). Diameter of amphid opening 2.5 wm. Eyes situated 73 to 80 wm from anterior end (1/13 to 1/14 esophageal length). Pigment bowl 12.0 wm x 10.0 wm; diameter of lens 5.0 um. Esophageal walls thick in this region. Two grooves with thick sclerotized walls form lens-shaped dilatations 15 to 18 wm from anterior end in wall of esophagus. Nerve ring situated 235 to 285 um from anterior end (1/4 esophageal length). Esophagus and genital tubes usual in size for such structures. Uterus occupies 2/3 of entire genital tube. Eggs 200 to 250 pm x 70 to 80 wm. Spicules straight, with rectangular head curved at an angle, and 90 wm long. Length of gubernaculum 25 wm. Accessory organ and anal papillae present but barely visible in my preparations.
The important characters distinguishing this species from others in the genus are: 1) lens-shaped expansions in anterior part of esophagus; and 2) straight spicules with almost rectangular head curved at an angle to the spicular body.
(.)
if
Figure 17. Leptosomatum bacillatum.
64
81
Geographic distribution. Black Sea (along the coastal strip among algae and on banks of mussels in silty and sandy benthos in a depth range of 10 to 96 m) and Mediterranean and Red Seas.
The distribution of this species given by Allgen is dubious. It is diffi- cult to explain its presence on the coast of Norway (1940a), the Pacific coast of Panama and California (1947c), the Hawaiian Islands (1951), and all along the coast of Argentina right up to Terra del Fuego (1959). The occurrence of this species in the subantarctic and on the coast of Norway are particularly questionable, especially since the author had only one female specimen for Norway. It seems to me that another species of this genus was involved. Identification of females of species of this genus is a very difficult task.
5. Leptosomatum elongatum Bastian, 1865 (Figure 18) Bastian, 1865: 145, pl. XII, figs. 156, 157; de Man, 1893: 103-107, pl. VI, fig. 9. 21-22 104-109 545-566 1,957-2,111 5,819-6,386
a 23-25 46-48 75-78 116-127 137-170 162-182 7,673-8,137 9,424-9,785 _10,850-12,360 : “Ca TY Se a=61-74; b=6; c=72-81; V =63-65%. 11-18 18-31 86-104 375-463 — 4,752-8,291
mote 14-23 31-42 34-48 54-73. 77-100 92-127 87-100 —
x 4,827-8,428 um; a—53-66; b—4-5; c—63-65.
Body rather long and tapers to 10/37 to 5/21 midbody diameter at anterior end and 5/6 to 5/7 at posterior end. Length of tail equal to width. Cuticle 8.0 to 9.0 wm thick, with fascicles of intersecting fibers. Cephalic capsule with rather thick walls; width at base exceeds length by 2.2 times. Cephalic ring rather massive. Cephalic setae short, 2.32 wm long (1/20 corresponding diameter). Cervical setae even shorter, 1.5 zm long. Amphids 29 to 34 wm from anterior end (1/60 esophageal length) and 7.0 wm in diameter (1/8 corresponding body diameter). Eyes situated 104 to 109 wm from anterior end (1/20 esophageal length). Pigment bowl 9.28 wm x 11.6 wm; diameter of lens 5.8 wm. Lips somewhat thick. Nerve ring situated 545 to 566 wm from anterior end (1/4 esophageal length). Length of anterior female genital tube 1,751 to 1,854 wm and reflexed part 1,030 to 1,236 um; of posterior tube 1,648 to 1,751 ym, and reflexed part 1,030 to 1,133 wm. In one female eggs 412 wm x 133 wm were de- tected in each uterine branch. Vulva surrounded by sclerotized granules and situated somewhat posterior to midbody.
Regrettably there was no male of this species in my material. Hence the distinctive features of this species are restricted to the cephalic struc-
82
{\\ ==a\\\
Figure 18. Leptosomatum elongatum Bastian.
65 ture, namely, its thick walls, cephalic ring situated in the upper part of capsule, and a distinct cephalic suture forming wide semicircular grooves separated by acicular projections.
Geographic distribution. This species in all probability is cosmopo- litan. It has been found in the Barents Sea (predominantly in the littoral zone among shells or in sand), the Mediterranean Sea, coast of California, tropical part of the Indian Ocean, coast of Australia, and in the Antarctic and subantarctic.
6. Leptosomatum punctatum (Eberth, 1863) (Figure 19) Eberth, 1863: 20, 21, tab. 2, figs. 5-7 (Phanoglene); Bastian, 1865: 145; Filip’ev, 1918: 48-50, tab. I, fig. 2. ' 8 105 350 1,080 — 7,905 12: 10 100 360 1,100 4,006 4,158 5,437 8,359 “25 48 80 90 — 120 — 90 a=70; b=8; c=76; V=49%.
8,470 um;
Body tapers to 1/3 midbody diameter at anterior end and 10/13 at posterior end. Cuticle bilayered; outer and inner layers equal in thick- ness, 6.0 wm on the average. Cephalic capsule thick-walled; width exceeds
6
fo)
83
length by 3.2 times. Cephalic suture barely discernible. Cephalic ring not distinct in my preparations; it appeared narrow and was situated mid- length of the head. Labial papillae short. Cephalic and cervical setae rather long. Cephalic setae 6.0 wm long (1/4 corresponding diameter); cervical setae slightly shorter, 5.0 um long. Amphids situated 30 um from anterior end (1/30 esophageal length); diameter of amphids 8.0 wm (1/3 corresponding diameter). Eyes situated 105 wm from anterior end (1/10 esophageal length). Pigment bowl 10 wm wide; diameter of lens 4.0 wm. Anterior margin of cephalic capsule forms rectangular depression in oral region which Filip’ev (1918) called a ‘‘pocket’’. Esophageal wall highly sclerotized near oral opening; thickening extends up to level of amphids. Esophagus rather narrow, almost not expanding posteriorly. Male spicules approximately uniform in width almost throughout their length, narrowing only in the distal (sharply curved) part in the middle, and 65 pm long. Gubernaculum 20 wm long. Accessory organ situated 112 wm anterior to anus. Anal papillae absent.
Figure 19. Leptosomatum punctatum.
Close to L. bacillatum, but differs in the following characters: 1) ce- phalic setae much longer, constituting 1/4 corresponding cephalic dia- meter versus 1/20 in L. bacillatum; 2) cuticular pockets present lateral to oral aperture in L. punctatum; and 3) spicules curved in middle portion (spicules straight in L. bacillatum).
Geographic distribution. Found mainly in the Black Sea in silt and among shells in a depth range of 40 to 100 m, and in algae of the coastal belt of the Mediterranean Sea.
84
7. Leptosomatum tetrophtalmum Saveljev, 1912 (Figure 20) Savel’ev, 1912: 124.
159: 23-29 104-116 __515_2,060-2,163 _7,004-6,901 * 93205 52-55 81-92 125-137 175-207 224-265 10,094-10,300 12,772-13,184 15,144-15,759 .. .
734-265 704-234 140-150 192206-19.934 pm:
458-73: b= 7_8: c= 91_94- V—61-65,,
Body very long and tapers to 1/4 midbody diameter at anterior end and 2/3 at posterior end. Caudal length slightly exceeds width. Cuticle thick, 9.3 to 10.4 um, with fascicles of intersecting fibers. Cephalic cap- sule well developed but its wall not very thick. Cephalic suture distinctly visible and slightly sinuous. Width of cephalic capsule exceeds length by 1.8 times. Thin cephalic ring situated in anterior third of cephalic cap- sule. Labial papillae rather large, distinct. Cephalic setae short, 3.5 wm long (1/15 corresponding diameter). Cervical setae 2.0 um long. Amphids with very thick wall, situated 23 to 34 wm from anterior end of body (equal to 1/60 to 1/90 esophageal length), spherical, and 7.0 wm in dia- meter (1/9 corresponding body diameter). Eyes situated 104 to 116 wm from anterior end (1/18 to 1/20 esophageal length). Pigment bowl 8.1 to 9.2 wm x 11.6 wm; diameter of lens 5.8 to 6.9 ym. Two more pigment spots situated posterior to original eyes. Oral cavity absent. Esophageal wall highly sclerotized in oral region. Nerve ring situated 515 wm from
So
Nh
Figure 20. Leptosomatum tetrophtalmum.
67
85
anterior end (1/4 esophageal length). Length of anterior female genital tube 3,090 to 3,399 um, and of posterior tube 2,678 to 2,884 um; respec- tive lengths of reflexed parts 1,751 to 1,854 and 1,339 to 1,442 wm. Sclero- tized granules occur around vulva on cuticle. Four to eight eggs 154 to 206 um x 154 to 185 wm found in each branch of uterus.
Distinguishing characters of this species: 1) large size; 2) presence of short setae; 3) thick-walled amphids, spherical in shape; and 4) presence of additional pigment spots without lens situated behind main eyes. The last feature is the most important from a diagnostic point of view.
Geographic distribution. Limited to the Barents Sea. Found in Lake Mogil’noe, Kola Bay, and on the shores of Novaya Zemlya.
8. Leptosomatum breviceps Platonova, 1967 (Figure 21) Platonova, 1967: 829, fig. 1.
ro, 6 87 382 1,184 — 4,377-7,779 * 17-34 104 112 125 — _ 104-105 c=79; V=56%.
Body tapers to 1/4 midbody diameter at anterior end and 10/13 at posterior end. Tail length equal to width. Cuticle 6.7 wm thick. Cephalic capsule extremely short; width exceeds length six times. Wall of cephalic capsule rather thin. Narrow cephalic ring passes medially through cephalic capsule. Cephalic suture straight. Labial papillae distinct; cephalic setae much longer than cervical ones. Length of cephalic setae 5.8 um (1/6 corresponding diameter), and that of cervical setae 1.2 wm. Amphids situated 23.2 um from anterior end (1/50 esophageal length).
7,879 um; a=56; b=7;
Figure 21. Leptosomatum breviceps.
69
86
Eyes situated 76 wm from anterior end (1/13 esophageal length). Pig- ment bowl 13.9 wmx 12.7 wm; diameter of lens 5.8 wm. Nerve ring situated 382 wm from anterior end (1/3 esophageal length). Vulva situated at midbody. Female specimen examined was sexually immature and hence tubes not visible.
Distinguishing features of this species: 1) extremely short cephalic capsule (width six times greater than length; 2) medial situation of ce- phalic ring in cephalic capsule; 3) rather long cephalic setae; and 4) short cervical setae, 1/5 length of cephalic setae.
Geographic distribution. This species has been found only in Kol’sk Gulf of the Barents Sea among Lithothamnion sp.
*9, Leptosomatum gracile Bastian, 1856 (Figure 22) Bastian, 1865; 145; pl. XII, figs. 158-160; Steiner, 1916: 610-620, tab. 16, fig. 27c, d; tab. 29, fig. 27a, b, e-g; tab. 30, fig. 27h-o (description).
1 2: L=13.3 mm; a=68; b=6; c=74.
Cephalic capsule very short and thin-walled. Cephalic suture at level of cephalic papillae. Labial papillae distinct and usually situated in a group of six somewhat posterior to oral opening. Cephalic setae trans- form into papillae. Contrary to all other representatives of this family in which the cephalic setae or papillae substituted for them are always ten in number and situated in one circle, in L. gracile only six cephalic papillae were detected by Steiner. Neither papillae nor setae occur on the body. Amphids large, situated a short distance posterior to lateral cephalic setae, and with notably thickened anterior wall. In addition to well- developed eyes with lenses, pigment spots of irregular shape also occur near the pigment bowls. Of the three lips encircling oral opening, dorsal one highly thickened, sclerotized, and markedly projects above the other two. Esophageal wall also sclerotized. Nerve ring encircles esophagus at border of its anterior third. Vulval opening encircled by rather thick scle- rotized lips. Cuticle around lips covered with minute sclerotized granules.
Despite the very brief description given by Bastian, Steiner noted the fallacy of making L. gracile synonymous with L. elongatum Bastian as done by de Man (1893). After studying specimens from the Barents Sea, Steiner arrived at the conclusion that species L. elongatum and L. gracile, although very similar, are nevertheless not identical.
Distinguishing features of this species: 1) cephalic capsule more weakly developed than in L. elongatum; 2) six cephalic papillae versus ten setae in L. elongatum; and 3) in addition to photosensitive eyes, irregular pigment spots also present in L. gracile.
Geographic distribution. Barents Sea and English Channel (shores of England).
87
"(Q16] ‘1OUISIg Woy) aj}o048 unjouosojdeT w oun
89
70
88 2. Genus Leptosomatides Filipjev, 1918
Filip’ev, 1918: 50, 51; 1922a: 98.
Type species: L. euxina Filipjev, 1918.
Nematodes of this genus highly resemble species of Leptosomatum in size, shape, and structure of cephalic capsule. Labial papillae distinctly visible, sometimes pointed, reminiscent of setae but usually short and blunt. Cephalic and cervical setae generally short. Unlike species of Leptosomatum, anal setae or papillae or sometimes both present in males of Leptosomatides. Amphids usually round and often taper toward posterior end. Oral cavity poorly developed. Vulva displaced pos- terior to midbody. Each spicule divided into two more or less equal parts—narrower proximal and wider distal. Occasionally velum situated on ventral aspect. Gubernaculum more complex than in species of Lep- tosomatum; always with paired capituli directed at right angles to spicular body. Dorsal process always present. Sometimes ventral process also present. Gubernaculum per se forms funnel around distal part of spicules. Well-developed accessory organ invariably present.
Key to Species of Genus Leptosomatides 1 (10). Amphids large; width exceeds one-eighth corresponding head
diameter. 2( 3). Cephalic setae long; length about one-fifth corresponding head diameter 32) keer a ie L. reducta Timm, 1959.
3( 2). Cephalic setae short; length does not exceed one-tenth corre- sponding head diameter. 4( 5). Small denticles present in anterior part of esophagus........ RONEN ee epee ots ORS L. antarcticum Mawson, 1956. 5 ( 4). Denticles absent in anterior part of esophagus. 6( 9). Sclerotized granules present on cuticle around vulva. 7( 8). Cervical setae reduced. Body slender (a=74 to 91).......... ne fensepinremn he ES cde aie eam 16. L. marinae sp. nov. 8( 7). Cervical setae present.......... 13. L. crassus Platonova, 1967. 9( 6). Sclerotized granules on cuticle around vulva absent.......... Ne ae PMN 12. L. inocellatus Platonova, 1967. 10 ( 1). Amphids small; width less than one-eighth corresponding head diameter. ; 11 (12). Labial papillae acicular and resemble setae.................. 12 (11). Labial papillae blunt, usual in shape. 13 (16). Gubernaculum with dorsal and ventral processes. 14 (15). Suture of cephalic capsule forms rather deep groove.......... ....L. conisetosum Schuurmans-Stekhoven and Mawson, 1955.
89
15 (14). Suture of cephalic capsule sinuous but does not form deep
PEOOVEN): HA ctoh seek ois idle @elole eens 15. L. brevisetosus sp. nov. 16 (13). Gubernaculum with only dorsal process. 17 (18). Males devoid of preanal papillac.................0.e seen, LOE Monae etal Po ee ms L. microlaimum Allgen, 1957
18 (17). Males with preanal papillae. 19 (20). Cephalic setae long; length one-ninth corresponding head dia-
IMELCT RR eee otis worn sel 9 toe a 10. L. euxina Filipjev, 1918. 20 (19). Cephalic setae short; length does not exceed one-twentieth corresponding head diameter.....11. L. steineri Filipjev, 1922.
10. Leptosomatides euxina Filipjev, 1918 (Figure 23) Filip’ev, 1918: 51-54, tab. 1, fig. 3; 1922a; 98-100, tab. 1, fig. 1. 11 100 470 1,800 — 8,877 1 3: 25GONIRS OSteL00 100. 8,950 ym, a= 89; p= 52 G=]0h, 1c: 14 113 555 1,815 4,567 7,768 8,897 10,988 PSO mSSrSsOMeO0n 11S 120.- fia 9s b=6; c=123; V=707%.
Body tapers to 2/5 midbody diameter at anterior end, but does not taper toward posterior end. Head narrow. Length of tail exceeds width by 1.2 times. Cuticle bilayered and 7.5 wm thick. Cephalic capsule with walls of average thickness. Cephalic suture distinct and only slightly sinuous. Capsule width exceeds length three times. Thin cephalic ring crosses cephalic capsule medially. Labial papillae small. Cephalic setae 4.0 wm long (1/9 corresponding diameter). Cervical setae slightly shorter, 3.0 um. Amphids small, rounded, 5.0 wm in diameter (1/8 corresponding body diameter), and situated 16 wm from anterior end (1/100 esophageal length). Eyes situated asymmetrically: one lies 80 wm and the other 140 pm from anterior end (1/20 and 1/13 esophageal length respectively). Pigment bowl 13 wm x 13 um; diameter of lens 4.0 wm. Esophageal wall highly sclerotized in oral region and markedly thickened at level of am- phids. Nerve ring situated 470 wm from anterior end (1/4 esophageal length). Two mature eggs, 430 wm x 90 wm, found in each uterine branch. Spicules of males unequal in length; left spicule 110 wm long and right 90 wm. Neither has a distinct capitulum. Proximal part of spicules uni- form in width, middle broadens considerably, almost doubles in width, and distal end blunt. Gubernaculum paired with fairly long processes, 65 wm. Ten pairs of protuberances with setae situated anterior to anus. Accessory organ present with lateral alate fortifying structures on cuticle.
Distinguishing features of this species: 1) location of amphids, which lie close to cephalic capsule, at a distance of 1/100 esophageal length from
71 anterior end; 2) thickening of esophageal wall at level of amphids;
11,078 um; a=92;
90
Figure 23. Leptosomatides euxina.
3) unequal length of spicules; and 4) unequal distance of eyes from ante- rior end. .
Geographic distribution. Limited to the Black Sea where it has been
found in depths ranging from 25 to 200 m among shells and in phaseolin and terebellid silts.
11.
Leptosomatides steineri Filipjev, 1922 (Figure 24) Filip’ev, 1922a: 98; 1946: 159, fig. 2; Platonova, 1967: 829.
2 11 116 463-469 1,390-1,499 — 10,660-10,769 3 34 45-46 81-83 110-112 112-120 120-125 115-125 x 10,780-10,894 wm; a= 85-90; b=8; c=87.
‘peut 104-116 433-510 1,566-1,823 5,686-6,973 99 42-52 81-94 122-132 *137=162 150-187 5,692-9,033 7,952-10,887 9, 703-12,844 * “155-287 145-200 1122137 22893 12,994 pm;
a=63; b=6-7; c=63-93; V=66-71%. 15-17 81-86 357-382 1,127-1,412 — 19-29 34-49 58-73 85-125 87-167 92-187
5,247-9,527 Mei ctu Alas pilots 4 aS 2105. 5,359-9,652 Lm, a2 59; eae 8; c=46-77.
10 juv.:
72
91
Body long, tapers to 1/3 to 1/4 midbody diameter at anterior end and 2/3 at posterior end in female; no posterior attenuation seen in male. Length of tail almost equal to width. Cuticle thick, 10 to 14 wm; fascicles of intersecting fibers present in outer layer. Cephalic capsule extremely short: width exceeds length by four times; wall very thick. Cephalic suture barely discernible and almost straight. Cephalic ring very narrow and lies in upper third of cephalic capsule. Labial 'papillae large. Ceph- alic setae extremely short, 2.3 wm long (1/20 corresponding diameter); cervical setae still shorter, 1.2 wm long. Amphids situated 17 to 29 um from anterior end (1/60 to 1/80 esophageal length). Amphids 6.9 um x 5.8 um; width 1/9 to 1/10 corresponding diameter. Eyes situated 116 wm from anterior end (1/12 to 1/15 esophageal length). Pigment bow] 9.3 pm x 12.7 wm; diameter of lens 8.1 wm. Nerve ring situated 433 to 510 yin from anterior end (1/3 esophageal length). Length of anterior female genital tube 1,236 to 2,575 wm, posterior tube 1,030 to 2,163 wm, and their reflexed parts 927-2,060 wm and 721 to 1,442 wm respectively. One egg, 412 to 515 wm x 133 to 154 wm, seen in each uterine branch. Male spicules smoothly arcuate in midsection; length 137 wm and width in narrowest part 17.5 wm and in widest part 25 wm. Gubernaculum with long (30 wm) process. One postanal and 17 preanal pairs of papillae present on tail. Accessory organ with complex sclerotized skeleton situ-
SS
Figure 24. Leptosomatides steineri (a—amphid).
73
92
ated anterior to anus at a distance of 125 wm and provided with four processes, two directed dorsally and two ventrally.
Distinguishing features of this species: 1) extremely short cephalic capsule; 2) extremely short cephalic setae; 3) smoothly curved spicules of equal length; 4) one pair of postanal and 17 pairs of preanal papillae; and 5) accessory organ with complex structural processes (dorsal and ventral).
Geographic distribution. Arctic species. Found in Kara Sea in depths ranging from 140 to 360 m in sandy silt.
12. Leptosomatides inocellatus Platonova, 1967 (Figure 25) Platonova, 1967: 829, fig. 1 (3, 4).
‘Dl y= 510), 1 146ge—— 9.83
29: 15-23 515-618 2,060-2,678 5,768-7,539 " 30-40 52-61 150-219 177-290 212-336 8,652-9,599 9,991-11,330 13,390-15,264 :
ep PSG 1622500 ae Ge a=45-58; b=6; c=70-108; V=52-64%. 14-17 408-463 1,390-1,644 — 5,764-10,660
2 JUV: 77-19 34-40 104-120 142-150 150-170 112-125
x 5,889-10,835 wm; a=39-64; b=4-8; c=47-62.
Body extremely long, tapers to 1/4 to 1/5 midbody diameter at anterior end and to 5/6 to 10/13 at posterior end. Length of tail almost equal to width. Cuticle very thick, 13 to 17 wm, bilayered, with intersecting fasci- cles of fibers in outer layer. Cephalic capsule short; width exceeds length three times. Cephalic wall rather thin. Cephalic suture faintly discernible and straight. Narrow cephalic ring situated medially in cephalic capsule. Labial papillae short. Cephalic setae short, but rather thick and massive, and 4.6 to 6.0 wm long (1/10 to 1/13 corresponding diameter). Cervical setae somewhat short, 3.5 to 4.0 wm long, situated in small pits, occasion- ally in groups of three to nine. Preanal setae of males significantly longer, up to 20 wm long. Amphids situated 29 to 35 wm (1/50 to 1/70 esophageal length) from anterior end, large, stretched longitudinally, 10.0 to 11.6 wm long, and width 1/6 corresponding diameter. Eyes absent. Nerve ring 510 to 618 wm from anterior end (1/4 esophageal length). Vulva median or posteromedian. Sclerotized granules around vulva absent. Length of anterior genital tube 1,545 to 2,884 wm, its bent part 1,133 to 2,678 um, of posterior tube 1,200 to 2,020 wm, and of reflexed parts 1,133 to 1,648 um. Sexually mature females with one egg 772 to 669 wm [sic] x 175 to 257 wm in each uterine branch. In females two to three pairs of papillae present on tail. Anterior male gonad 262 wm and posterior 1,442 ym long. Spicu- les equal in length but different in shape; right spicule smoothly arcuate,
93
with slightly thickened capitulum, followed by neck (cervix) widening into spicular body; left spicule significantly more irregular in shape. Spicular length 237 wm. Length of gubernaculum 50 ym. Accessory organ situated 150 «zm anterior to anus. Setae in anal region number 20 pairs, of which
6 are postanal. Anterior to these setae lie 17 pairs of papillae.
74
47, »\ : ‘ a Q
igh
= =
— 72
—= — \
=——
@ 4 7 Po) —$——_ 4’ SSS —————————
Au
AAA AAT
——
7 a oF a Ld a.
|
|
Figure 25. Leptosomatides inocellatus.
Distinguishing features of this species: 1) extremely thick cuticle; 2) cervical setae gathered in groups in small pits; 3) large amphids, stretched longitudinally; 4) complete absence of eyes and photosensitive pigment; 5) presence of two to three pairs of papillae on tail of female; 6) absence of sclerotized granules around vulva; 7) spicules significantly different in shape; and 8) presence of 20 pairs of setae and 17 pairs of papillae in anal
region of male. Geographic distribution. To date found only in the Kara Sea at depths
ranging from 200 to 800 m.
13. Leptosomatides crassus Platonova, 1967 (Figure 26) Platonova, 1967: 829-831, fig. 1 (5-7)
5 9: 13-23 98-109 412-433 " 21-26 43-48 81-89 125-150 6,407-7,828 9,191-9,888 9,497-12,154 9,622-12,329 pm:
200-212 225-250 135-150 a=48-51; b=7-8; c=70-77; V=64-67%.
1,463-1,669 5,580-5,665 167-200 217-250
7
.o7)
94
10-11 50-63 220-270 980-991 —_— 18-21 28-31 50-58 76-82 95-105 115-120 2,052-4.°87 4 003-4,437 um; a=30-35; b=4; c=30-34. 90-95.
Body tapers to 1/5 midbody diameter at anterior end and 5/8 at post- erior end. Length of tail almost equal to width. Cuticle thick, 11.6 to 14.0 wm, with fascicles of intersecting fibers in outer layer. Cephalic capsule with rather thick wall but poorly expressed cephalic suture; width exceeds length by 2.5 times. Extremely narrow cephalic ring situated in upper third of cephalic capsule. Labial papillae distinct. Cephalic setae extremely short, 2.32 wm in length (1/20 corresponding diameter). Cervi- cal setae 1.6 um long. Amphids 23 to 34 ym from anterior end (1/60 esophageal length) and 8.0 to 7.0 wm wide (1/6 to 1/8 corresponding dia- meter). Eyes 98 to 109 wm from anterior end (1/14 to 1/15 esophageal length). Pigment bowl 8.12 wm x 15.08 um; diameter of lens 7.0 to 8.0 pm. Esophageal wall sclerotized in oral region. Nerve ring 412 to 433 wm from anterior end (1/3 esophageal length). Length of anterior female genital tube 1,957 to 2,575 yum, of posterior tube 1,554 to 2,060 wm, and
5 juv.:
mn"
Figure 26. Leptosomatides crassus (below vulva).
95
of reflexed parts 515 to 1,030 wm and 824 to 927 um respectively. Four to eight eggs, 154 to 360 wm x 824 to 206 wm, found in uteri.
This species is distinguished from others in the genus (except L. stein- eri) by the following features: 1) long and broad body covered with thick cuticle; 2) relatively long cephalic capsule; and 3) extremely short cephalic and cervical setae. L. crassus differs from L. steineri in: 1) wider body; 2) cephalic capsule almost two times longer; 3) amphids situated closer to anterior end; 4) esophageal wall much thicker in oral region; 5) greater number of eggs in uteri of L. crassus (up to eight) than in L. steineri [in my material only one each, but according to Filip’ev (1946) up to four]. It should be noted that Filip’ev (1916) gives more taxonomic importance to such characters as size and number of eggs.
Geographic distribution. Found only in the Barents Sea in the littoral zone, predominantly under offshoots of brown algae.
14. Leptosomatides acutipapillosus sp. nov. (Figure 27) Holotype 9: Institute of Zoology, Academy of Sciences, USSR. Col- lection No. 7034.
17 92 463 1,802 5,922 8,909 11,896 13,441
SS 7g tl SGI nt pee
a=68; b=7; c=91; V=66%.
Paratypes.
Te 17 92-109 459-463 —1,695-1,802 5,929-6,330 195279 467 R= 100M 125137 622177 187-242 8,909-9,214 11,896-12,201 13,441-14,466 *~ 192-225 200-212 (P50 ee Coe
a= 65-68; b=7-9; c=84-91; V=62-66%. 10-17 69-104 300-408 969-1,438 Me
12 juv.:
14-25 31-46 48-98 72-150 97-175 120-187
SDB 25? 5,429-8,469 wm; a=44—48; b=5-6; c=44-70. 87-125
Body tapers to 1/4 to 1/5 midbody diameter at anterior end and 5/7
to 2/3 at posterior end. Head round, tail small, slightly conically stretch- ed and bluntly rounded at end. Length of tail exceeds width by 1.2 times. Cuticle bilayered, 9.0 to 10.0 wm thick, with fascicles of intersecting fibers situated in outer layer. Cephalic capsule with fairly thin wall and barely discernible suture. Narrow cephalic ring situated in upper third of ce- phalic capsule. Width of latter exceeds length by 2.7 times. Labial papil- lae with characteristic structure, pointed, and resemble setae. Cephalic setae short, 3.5 wm in length (1/13 corresponding body diameter). Cervi- cal papillae 2.3 um long. Amphids 29 wm from anterior end (1/60 eso-
76
96
phageal length) and 8.1 wm wide (1/7 to 1/8 corresponding body diameter). Eyes 92 to 109 ym (1/16 to 1/18 esophageal length). Pigment bowl 10.4 to 12.7 wm; diameter of lens 7.0 wm. Nerve ring situated about 1/4 length of esophagus from anterior end. Length of anterior female genital tube 2,884 to 2,987 um, of posterior tube 2,987 to 3,000 um, and of reflexed parts 2,060 to 1,751 and 1,554 to 1,957 wm respectively. Two to eight eggs, 154 to 257 wm x 133 to 154 wm, found in each uterus.
Figure 27. Leptosomatides acutipapillosus sp. nov.
Distinguishing features of this species: 1) conically stretched but ob- tusely rounded tail of female; 2) labial papillae pointed and resemble thick setae. Thick cuticle, relatively long cephalic capsule, and amphids with large openings are also characteristic of this species. Structurally close to L. crassus but further distinguished from it by shape of tail, pointed labial setae, somewhat wider cephalic ring and its lower position, and longer cephalic setae.
Geographic distribution. The only place of occurrence of this species has been the Sea of Okhotsk; found at a depth of 25 m in silted benthos.
15. Leptosomatides brevisetosus sp. nov. (Figure 28) Holotype 3: Institute of Zoology, Academy of Sciences, USSR. Col- lection No. 6128.
25 92 515 1,799 — 10,825
sagdGy GOMODASIIDAISO MOD Nee ee Boone
77
97
Paratypes. gg, —_1O-IL__81-92_450-515_1,799-1,854 «S124 AG=5 286270 8221005) 11 25125° 1252130 TS?! 10,000-12,000 um; a=73-92; b= 6-7; ¢=62-84. 93.9; 11-23 __ 92-125 470-618 1,892-2,472 5,022-8,170 * 32-34 42-50 76-87 120-145 167-180 170-175 10,000-11,951 10,935-14,938 11,800-17,441 *—~T80-250 ED=DOO\ sic MA0LISOT ac, a= 56-80; b=6-8; c= 70-100; V = 75-80%.
Body tapers to 2/5 to 1/3 midbody diameter at anterior end and 10/13 to 5/8 at posterior end. In males body in region of spicular apparatus somewhat wider than midwidth. Cuticle thick, 7.5 wm, with fascicles of intersecting fibers in outer layer. Labial papillae short but very wide. Cephalic and cervical setae papillate, very short, with rounded ends. Length of cephalic setae 2.0 wm (1/15 to 1/16 corresponding diameter). Cephalic capsule short; length 2.8 times less than width. Cephalic suture barely discernible and sinuous. Cephalic ring shifted more anteriorly: situated in first quarter of capsule. Lips sclerotized. Faily large amphids, width 8.12 wm (1/8 corresponding diameter), situated 25 to 32 wm from anterior end. Eyes 81 to 100 wm from anterior end. Pigment bowl 11.6 pm x 11.6 wm; diameter of lens 5.8 wm. Nerve ring 450 to 618 wm from anterior end (1/4 esophageal length). Length of anterior female genital tube 3,000 to 3,200 um, of posterior tube 2,884 to 2,900 um, and of re- flexed parts 1,700 to 1,820 um and 2,000 to 2,060 um respectively. Vulval lips thick and muscular with upper lip covering lower one. Genital arma- ture of male represented by spicular apparatus, accessory organ, seven to nine pairs of pretubal, and one pair of postanal papillae. Length of spicules 140 to 170 wm. Each spicule divided into two parts: distal part significantly wider than proximal. Gubernaculum with dorsal and ventral processes. Accessory organ 150 to 160 wm from anus, with sclerotized cyathiform supports with two alate processes, one proceeding anteriorly and the other posteriorly.
Distinguishing features of this species: 1) amphids situated at a dis- tance equal to two cephalic lengths from anterior end of body, i.e. situated farther away from anterior end compared to other species of the genus; 2) characteristic shape of amphids, anteriorly wide and tapering rather abruptly posteriorly; 3) absence of anal setae; 4) pretubal and postanal situation of papillae in-males, but no papillae between anus and accessory organ; 5) cyathiform sclerotized structures with alate processes support- ing accessory organ from inside; 6) distinct division of spicules into narrow proximal part and wide distal part; 7) presence of dorsal and
98
Figure 28. Leptosomatides brevisetosus sp. nov.
ventral processes on gubernaculum; and 8) extremely short, papillate ce- phalic and cervical setae.
Geographic distribution. Sea of Okhotsk (Kuril Islands). Found in the littoral zone under offshoots of algae and in sandy benthos.
16. Leptosomatides marinae sp. nov. (Figure 29) Holotype 3: Institute of Zoology, Academy of Sciences, USSR. Col- lection No. 7880.
18 84 465 1,834 — 12,474 24 40 70 140 145 169 148
12,633 wm; a=75; b=9, c=80.
Paratypes. =, 16-18 | 78-91 /399%465 1 7202,061 3: 54-96 38-48 70-80 120-145 142-160 137-169 10,573-14,323 an te ee 189 10,719-14.522 um; a= 75-94; b=6-7; c= 73-80. 2g. 15-23 78-96