A Scanning Electron Microscope Study of Them As Sublateral Setae Reminiscent of Phasmids and Somespecies of Terrestrial Nematodes From' Spitzbergen

The taxonomic position of some teratocephalid nematodes

- a scanning electron microscopeA study

Sven BOSTROM” University of Stockholnz, Department of Zoology, 106 91 Stockholm, Sweden.

SUMMARY Four teratocephalid species, viz. Metateratocephalus crassidens, Teratocephalus costatus, T. lirellus and T. terrestris, were studied by SEM, which provided additional information on anterior organization and external morphology.Al1 species have six leaf-like lips, separated by incisures about half the lip length in M. crassidens and by deep incisures almost the whole lip length in Teratocephalus, supported by strongly sclerotized margins.In M. crassidens subdorsal and subventral lips beartwo setiform sensilla each, lateral lips only one.In Teratocephalus subdorsal and subventral lips bear a single setiform sensillumat the base. The weakly annulated and minutely punctated cuticle of M. crassidens has scattered pores anteriorly and pores posteriorly along both sides of the lateral fields, which are coarsely punctated anteriorly and consist of expanded cuticle from Inmidbody. Teratocephalus lateral fields are demarcated bytwo incisuresand usually distinctly offset.The possible plesiomorphic or apomorphic state of some external characters are discussed and in the light of this the taxonomic position of the teratocephalids.

RESUME

Position taxinomique de quelques nématodes Tératoceplzalides - une étude au nzicroscope e7ectmnique à balayage Quatre espèces de Tératocéphalides - Metateratocephalus crassidens, Teratocephalus costatus, T. lirellus, T. terrestris - ont été étudiées au microscope électronique à balayage, apportant ainsi des données complémentaires sur l’organisation de la partie antérieure et la morphologie externe. Toutes les espèces ont six lèvres foliacées, séparées par des incisures, longues de la moitié des lèvres chezM. crassidens, et de la longueurde celles-ci chez Teratocephalus; ces lèvres sont soutenues par des marges fortement sclérotisées. Chez M. crassidens, les lèvres subdorsaleset subventrales portent chacune deux sensilli sétiformes et les lèvres latérales un seul. Chez Teratocephalus, les lèvres subdorsales et subventrales portent un seul sensillum, à leur base. La cuticule de M. crassidens, faiblement annelée et pourvue de fines ponctuations, présente des pores irrégulièrement disposésa la partie antérieure, et situés de part et d’autredu champ latéral à la partie postérieure du corps.Le champ latéral est fortement ponctué antérieurement et consiste en une expansion de la cuticule à partir du milieu du corps. Chez Teratocephalus les champs latéraux sont délimités par deux incisures et le plus souvent distinctement en relief. L’état supposé plésiomorphique ou apomorphique de certains des caractères externes est discuté, de même que, à la lumière de ceux-ci, la position taxinomique des Tératocéphalides.

Species of the genera Metateratocephalus Eroshenko, probable that the teratocephalid genera are more dis- 1973 and Teratocephalus de Man, 1876 were recorded tantly related to each other than many present classifi- from Spitzbergen by Loof (1971). His survey of terres- cation schemes reflect. trialnematodes was based on alarge collection per- In thispaper four species of teratocephalids(one formedin July 1965 by Mr. H. vanRossen inthe Metateratocephalus, three Teratocephalus) are studied by western part of the island. A smaller collection of soil SEM inorder to add further information on the anterior samples, fromroughly the same area, was made by organization and on theexternal morphologyin general. Mr. G. Rudback in July 1985. So far this collection has The possible ancestral or derived stateof some external resulted in the description of a new cephalobid species characters studied and thetaxonomic positionof the two (Bostrom, 1987) anda scanning electron microscope genera is also discussed. (SEM) study of a plectid and some cephalobid nema- rodes (Bostrom, 1988). The taxonomicposition of the teratocephalids has Material and methods been,much discussed and the genera have often been collectively placed either close to thecephalobids (in the The western part of Spitzbergen, from Longyearbyen Secernentëa) or close to the plectids (in the Adenopho- in thesouth to Amsterdamoya in thenorth, was sampled rea) (see discussion ” for details). It is,however, in July1985. Twentyfour samplesof loamy soil to about S. Bostrom

6 cm depthwere collected with a small corer.They were REMARKS transported in capped plastic tubes and subsequently nematodes were extracted by awet funnel method The specimens are in agreement with the population (Sohlenius, 1979). described as Euteratocephalus crassidens(de Man, 1880) The nematodes were heat-killed, fiied in cold TAF, Andrassy, 1958 from Spitzbergen by Loof (1971), and transferred to glycerine by a slow evaporation method further extend the ranges of some measurements and (Hooper, 1970) and mounted on slides forlight mi- ratios forthe species (Andrassy, 1984). Loof pointed out croscopy (LM) as described in Bostrom and Gydemo that his specimensdiffered fromde Man’s types in having a longer tail (cf = 5-6 cf = but they are (1983). For SEM,specimens were postfiied in 1 O/O OsO, vs. 5), in redistilled water for one hour and dehydrated in an within the ranges (c‘ = 4.5-6) given in Andrassy (1984) acetone/redistilled water series to pure acetone. They for M. crassidens. Andrassy (1984) synonymized M. were critical point dried, mountedon stubs, coated with typicus Eroshenko, 1973 with M. crassidens, an action gold and examined in the SEMas described in Bostrom not followed by Zell (1986). Andrassy later (1985) de- and Gydemo (1983). scribed a new species, M. gracilicaudatus, distinguished The nematodes were identified to species level in the by a more slenderbody, a wider head and a much longer, LM. filiformtail. Inthis species “ phasmids ” were not observed. The taillength of M. gracilicaudatus (56-62 pm) is similar to that found in thespecimens of (deMan, 1880) Metateratocephaluscrassidens M. crassidens here (52-66 Pm), but the c‘-ratios (7-8 vs. Eroshenko, 1973 5-6) and vulva-anushail-ratios (2-2.5 vs. 2.6-3.9) differ. (Fig. 1) The populationdescribed here is thus regarded as ,. MEASUREMENTS belonging to M. crassidens. Fernales (n = 10) : L = 430-620 pm (505 f 21); a = 21-30(24 f 1); b = 3.9-4.7 (4.3 rf: 0.1); Teratocephalus costatus Andrissy, 1958 c = 7.8-10.5 (8.8 f 0.3); cf = 5.0-6.0 (5.4 k 0.1); (Fig. 2) V = 50-55 (53 f 0.4); vulva-anushail = 2.6-3.9 (3.1 f 0.4). MEASUREMENTS Males :not found. Fernales (n = 3) : L = 510-570 pm;a = 24-27; b = 3.4-3.9; c = 5.9-6.5; C’ = 7.9-8.7; V = 53-59; DESCRIPTION vulva-anus/tail = 1.5-1.8. Head distinctlyoffset by constriction. Six broad Males :not found. leaf-like lips, separated by incisures about half their length, supported by sclerotized margins; internallythe DESCRIPTION lips are supported by radial ridges connecting to the tangential ridges surroundingthe stomatal aperture Head offset without cervical expansion. Six leaf-like (Fig. 1 A-B). Each subventral and subdorsal lip bears lips (about 3.5 pm high), separated by deep incisures two setiform sensilla, the anterior about 3.5-4 pm long almost the whole lip length and supported by strongly and theposterior somewhat shorter (about3 pm), which sclerotizedborders, which arerounded apically enterthrough medianperforations thein lips (Fig. 2 A). The lips are supported internally by radial (Fig. 1 A-B). The laterallips bear only the anterior ridges connecting at the tangential ridges that surround sensillum. Amphids large (about 5 pm diameter) and the stomatal opening.The subdorsal and subventral lips circular, about 10-12 Fm from base of lips (Fig. 1 C). bear a single setiform sensillum basally (Fig. 2 A, C). Cuticle vaguely annulated and finely punctated; scat- The small porelike amphid opening is positioned in the tered pores anteriorly and posteriorly along both sides first transverse body stria (Fig. 2 A). First body annule of the lateral fields (Fig. 1 C, F). Excretory pore round broad,sloping anteriorly; second and third annules (aperture about 1 Pm), at level of metacorpus (Fig. 1D). compressed;the following four to six annulesabout Lateral fields coarsely punctated anteriorly (Fig. 1 E), 1-1.5 pmbroad; from the eighth-tenthannules, the from midbody an expanded cuticle (Fig. 1 F). Vulva a annulesare broader (2-2.5 pm)and the longitudinal transverse slit with many radially arranged narrow cu- ridges (n = 8)commence (Fig. 2 C). Excretorypore ticularridges (Fig. l G). Anal aperture atransverse (aperture about 0.5 pm) surrounded by raised cuticle slit witha long posterior lip and apostanal depres- incisedanteriorly (Fig. 2 D). Lateral field with two sion (Fig. 1 H). A pair of lateroventral setiform papillae crenate incisures (Fig. 2 B). Vulva a transverse indented justposterior to anus (Fig. 1 F, H). Tail always at- slit (Fig. 2 E). Anal aperture a transverse slit with the tractsdetritus which mayindicate presence ofse- posteriorlip somewhat protuberant (Fig. 2F). Tail cretions, although caudal glandS.have not been observ- elongate (79-96 pm) with a bifid terminus; phasmidsnot ed. seen (Fig. 2 F).

182 Revue Néwlatol. 12 (2) :181-190 (1989) SEM study of teratocephalids S. Bostrtim

...

Fig. 2. TeratocephaZus costatztsAndrassy, 1958. A : Head, lateral view; B : Lateral field; C : Anterior end; D : Excretory pore; E : Vulva; F : Tail. (Bar on A, C, D = 1 Pm; on B, E = 2 Pm; on F = 4 Pm.)

184 Revue Nérnatol.(1989) 12 (2) :181-190 SEM study of teratocephalids

~ ~~~~

REMARKS b = 4.7-4.9; c = 3.5; c' = 17.5-18.0; V = 47; vulva- anusltail = 0.8-0.9. The specimens agree withthe population Loof (1971) described as T. decarinus Anderson, 1969 from Spitz- Males :not found. bergen apart from a relatively longer tail (c = 4.8-5.7; c' = 9-1 1; vulva-anusltail = 1.4-1.5) in Loof s speci- DESCRIPTION mens. In theoriginal description by Anderson (1969) of i': decarinus, its tail length ranges from 69 to 103 pm The anterior organization is very similar to that of 7: (c = 5.5-6.8). Loofdiscussed the minordifferences lirellus (cf. Figs 3 C and 4 A). Head offset with cervical between T. costatus and T. decarinus. Andrassy (1984) expansion and prominent cephalic ribs (Fig. 4 A). The synonymized the two species and the specimens de- lips appear very angular apically (Fig. 4 A). Amphids as scribed here are within the ranges of i': costatus estab- in the othertwo species. First annule broad and sloping lished by him. anteriorly; second annule about 1 pm broad; the following body annules 1.5-2 pm broad. Excretory pore (aperture about 0.5 pm) with raised cuticular margins Teratocephalus 1it.ellus Anderson, 1969 incised anteriorly (Fig. 4B). Anterior to thelateral field, (Fig. 3) bosdered by two incisures, there are about 25 perfor- ationsbetween the annules (Fig. 4 C). Perforations MEASUREMENTS (about 15) were also found ventrally in the same region Females (n = 3) : L = 515-575 pm;a = 28-38; (Fig. 4 C). Vulva a transverse slit with protruding lips b = 4.3; c = 4.0-4.2; C' = 13.6-16.4; V = 49-51; (Fig. 4 D, F). Anus a transverse slit with posterior lip vulva-anusltail = 1.O- 1.1. protruding.Tail elongate (162-177 Pm) with minute bifurcation at terminus; phasmids notobserved. The tail Males :not found. on Fig. 4 E is unfortunately broken and the terminal bifurcation can not be seen. DESCRIPTION

The general anterior organization is similar to that REMARKS foundin T. costatus. Head offset;a distinct cervical expansion with prominent cephalic ribs (Fig. 3 C). The These specimens differ from i': lirellus mainly in the lips are somewhat higher (about 4 pm) and more trunc- lack of longitudinal body ridges. The tails are much ate than in T. costatus (Fig. 3 A, C). Small, porelike longer than in thespecimens of T. lirellus (129-136 pm) amphids in first body stria (Fig.3 A). First body annule described above, but are within the range (81-177 pm) broad,sloping anteriorly; second annule plain; from of the original descriptionof i': lirellus (Anderson, 1969). third annule longitudinal ridges (about 18 at midbody) Loof (1971) stated that T. lirellus is immediately dis- start to appear (Fig. 3 C). Excretory pore (aperture ca. tinguished from T. terrestris on account of the very long 0.5 pm) with margin of raised cuticle incised anteriorly tail and the pre-equatorial vulva. That the distribution (Fig. 3 B). Lateral field conspicuous with two incisures of T. terrestris is very uncertain due to confusion with (Fig. 3 D). Vulva atransverse slit with prominent closely related species was pointedout by Andràssy protruding lips (Fig. 3 F). Anus a transverse slit with (1984) and Zell (1986) also stressed the unreliability protuberantposterior lip (Fig. 3 E). Tail elongate in theinformation on thespecies. These specimens will, (129-136 Pm) with minute terminal bifurcation; phas- however, be provisionally determined as T. terrestris as mids not observed (Fig. 3 E). they lack the longitudinal ridges typical of T lirellus. REMARIZS Discussion The specimens agreewell with the original description of T. lirellus by Anderson(1969) and with the population As stated in the introduction, the taxonomic position described by Loof (197 1) from Spitzbergen, although of the teratocephalids has been much debated and they Loofs specimensagain had relatively longertails have been variously placed under the classes of nema- (c = 2.3-3.5; c' = 19-35) than recorded here. todes. AndrAssy (1958) proposed the family Teratocephali- Teratocephalus tewesttis (Bütschli, 1873) dae and considered it transientbetween the families de Man, 1876 Cephalobidae (Filipjev, 1934) Chitwood & Chitwood, (Fig. 4) 1934 and Mectidae Orley, 1880 [i.e. between the classes Phasmidia (Secernentea) and Aphasmida (Adenopho- MEASUREMENTS rea)]. Goodey (1963) gave it status of an order, Teratoce- Fe~nales (n = 2) : L = 560-620 Pm; a = 34-37; phalida, which he placed betweenthe orders Rhabditida

Revue Nématol. 12 (2) : 181-190 (1989) 185 S. Bostrom

Fig. 3. Teratocephalus lirellus Anderson, 1969. A : Head slightly tilted, lateral view;B : Excretory pore; C : Head, sublateral view; D : Lateral field; E : Tail; F : Vulva. (Bar on A-C = 1 Pm; on 0, F = 2 pn; on E = 10 pm.)

186 Revue Nématol. 12 (2) :181-190 (1989) SEM study of teratocephalids

Fig. 4. Teratoceplzalus terrestris(Biitschli, 1873) de Man, 1876. A : Head, sublateral view; B: Excretory pore;C : Ventral and lateral perforations and lateral field anteriorly;D : Lateral field and vulva; E: Tail; F : Vulva. (Bar on A, B, 0, F = 1 pnz; on C = 4 p?z; on E = 10 pm.)

Revue Nématol. Revue (1989) 12 (2) : 181-190 187 S. Bostrom and Araeolaimida as it shows a mixture of characters of bour the taxa not belonging to the Chromadorida, and these orders. the Teratocephalidae was placed in this new suborder. Maggenti (1963) put thefamily Teratocephalidae Some other authors have recently (Inglis, 1983; Poi- Andrassy, 1958 in a basal position on the secernentean nar, 1983) placed the teratocephalids under the Araeo- branch close to the Cephalobidae. laimida (subclass Chromadoria). Inglis (1983) further- De Coninck (1965 b), Eroshenko (1973), and Gerlach more splitted them intotwo families [viz. Teratocephali- and Riemann (1973) placed the family in the Araeolai- dae and Metateratocephalidae (Eroshenko, 1973) Inglis, mida close to the plectids. 19831, which he suspected should be referred to differ- Andrassy (1976, 1984) put the suborder Teratoce- ent orders. phalina Andrassy, 1974 in the Rhabditida between his Apart from the resemblances in the anterior organiz- subclass Torquentia and what he refers to as the true ation, which may be due toconvergence, there is rather Secernentia; although he pointed out (1976) that it is a much that may cal1 for a further taxonomic separation peculiargroup [also embracing the Chambersiellidae of the genera Metateratocephalus and Teratocephalus. (Thorne, 1937) Sanwal, 19571. Andrassy (1976) con- Some differences betweenthe two genera as seen by the fessed that he was inclined to include a part of the SEM are listed in Table 1. There are also differences Teratocephalina in the Torquentia (Chromadorea), but regarding the female and male reproductive organsand in the species showing the largest number of Torquentia possibly also in the pharynx organization (i.e. the basal characters phasmids are present.He furtherstated that : bulb), but these characters have not been studied here. " The whole suborder of Teratocephalina gives the It would perhaps be fruitful to discuss some of, the impression that theywere just about tochange from the characters on Table 1 in terms of being plesiomorphic Torquentia-type into the Secernentia-type ". (ancestral) or apomorphic (derived). Lorenzen (198 1, 1983), on the otherhand, found no The external cuticle structure of Metateratocephalus indication that the caudal setae of M. crassidens and with minute punctations and pores(possibly connected related species are phasmidsand did nothesitate to place with the hypodermis) anteriorly and along the lateral the Teratocephalidaein the Adenophorea.Lorenzen fields may resemble thatfound in some species of (1981) Split the Araeolaimida. Taxa with outstretched Chromadorida (Wright & Hope, 1968). It is presumably ovaries were transferred to the Monhysterida and those plesiomorphic to thedistinctly annulated cuticleof Tera- with antidromous reflexed ovaries to theChromadorida. tocephalus. He also erected a new suborder, Leptolaimina, to har- The basic, and thus assumed plesiomorphic, external

Table 1 Some differences between the genera Metateratocephalus Eroshenko, 1973 and Teratocephalus de Man, 1876 as recorded by the scanning electron microscope.

Character Metateratocephalus Teratocephalus

Cuticle Weakly annulated, minute punctations; pores Distinctly annulated, withlwithout longitudinal anteriorly and along lateral fields ridges Cephalic sense organs Subdorsal and subventral lips bear twoseti- Subdorsal and subventral lips bear one setiform sensilla,lateral lips bear one setiform form sensillurn basally sensillum Amphids Postlabial, large, round (semi-spiral), 10-12pm Postlabial, porelike,in first body stria, 2.5-3pm posterior to base of head posterior to base of head Excretory pore Minute opening (about 1 pm in diameter) Minute opening (Ca. 0.5 pm wide) with margins of raised cuticle Lateral field Coarselypunctated anteriorly, expanded cu- Bordered by two incisures, usually distinctly ticle posteriorly offset Vulva opening Transverse slit with numerous radially arraned Transverse slit with protruding lips (depressed cuticular ridges in X cosratus) Anal aperture Transverseslit with longposterior lip and Transverse slit with posterior lip protruding post-anal depression Phasmids Possibly analogous lateroventral setiform papil-Not observed lae just posterior to anal aperture

~~~ ~~~

188 Revue Nématol. 12 (2) :181-190 (1989) SEM study of teratocephalids organization of cephalic sense organs is six inner labial organization of the valvular structures in thebasal bulb, sensilla, six outer labial sensilla, four cephalic sensilla and 4) the organization of the caudal setae (phasmids?) and two amphids (De Coninck, 1965~).Metateratoce- in Metateratocephalus must be carried out. phalus is close to thispattern : six, probablyouter, setiform labial sensilla, four setiform cephalic sensilla ACKNOWLEDGEMENTS and two amphids. The inner labials may be present in the form of minute papillae, but have not been traced. The author is grateful to Dr. Bjorn Sohlenius for reading andcommenting on the manuscriptand to Mr.Goran In Teratocephalus thenumber of external sensilla is Rudbgck for providing soil samples from Spitzbergen. reduced to foursetiform cephalicsensilla, the inner and outer labials have not been observed, and two amphids. The longersetiform sensilla of Metateratocephalus REFERENCES probably also represents a more plesiomorphic condition ADAMSON, M. L. (1987). Phylogenetic analysis of the higher than theshorter sensilla of Teratocephalus in accordance classification of the Nematoda.Can. J.Zool.,65 : 1478-1482. with the generalagreement presented by Adamson ANDERSON, R.V. (1969). Comparative morphology and de- (1987). scriptions of three newspecies of Teratocepkalus from The more posterior position of the amphids in Me- Canada. Can. J. Zool., 47 : 829-840. tateratocephalus is probably plesiomorphic to the more ANDRASSY,1. (1958).Erd- und Siisswassernematoden aus anteriorly placed in Teratocephalus asproposed by Bulgarien. Acta zool. hung., 4 : 1-88. Adamson (1987). Also the large circular(or semi-spiral) ANDRASSY,1. (1976). Evolution as a basisfor the systematization amphids of Metateratocephalus is plesiomorphic to the of nematodes. London, Pitman Publishing, 288 p. pore-like amphids of Teratocephalus (Adamson, 1987). The modified, coarsely punctatedand expanded, ANDRASSY,1. (1984). Klasse Nematoda.In : Besti?nmungsbiiclter cuticle making up thelateral fields in Metateratocepha- zur Bodenfauna Europas. Stuttgart, Gustav Fisher Verlag, lus are possibly plesiomorphic tothe differentiated, 509 p. more or less offset, lateral fields of Teratocephalus as ANDRASSY,1. (1985).A dozen new nematode species from discussed by Adamson (1987). Hungary. Qpusc. zool., Bpest, 19/20 : 3-39. The caudal lateroventral setae of M. crassidens are BOSTR~M,S. (1987).A new terrestrial nematode species regarded as phasmids by Andrassy (1958, 1976, 1984) (Rhabditida : Cephalobidae) from Spitzbergen. Polar Biol., andsome authors (e.g. Goodey,1963; Loof, 1971) 7 :375-378. followed his interpretation. Eroshenko (1973) described BOSTR~M,S. (1988). A scanning electron microscope study of them as sublateral setae reminiscent of phasmids and somespecies of terrestrial nematodes from' Spitzbergen. Lorenzen (1981, 1983) pointed outthat there is no Nematologica, 33 (1987) : 366-374. indication of these structures being phasmids. Andrassy BOSTR~M,S. & GYDEMO,R. (1983). Intraspecific variability in (1984) alsoclaims to have observed distinct phasmidsin Acrobeloides nanus (de Man) Anderson (Nematoda, Cepha- Euteratocephaluspalustris (de Man, 1880)Andrassy, lobidae) and a noteon external morphology. Zool. Scr., 12 : 1958. Neithercaudal setae nor phasmids have been 245-255. observed in species of Teratocephalus and it is thus not DE CONINCK,L. (1965~).Classe des nématodes. In : Grassé, possible to judge which genus is plesiomorphic in this P. P. (Ed.) Traité de Zoologie. Vol. 4 (2) Némathelminthes. respect. Paris, Masson & Cie : 1-217. There are, thus, data indicating that a further sep- DE CONINCK,L. (1965b). Syhématique des nématodes. In : aration of the genera Metateratocephalus (probably Grassé, P. P. (Ed.) Traité de Zoologie. Vol. 4 (2) Némathel- togetherwith Euteratocephalus Andrassy, 1958) and minthes. Paris, Masson & Cie : 586-681. Teratocephalus is necessary. The position of the genus EROSHENKO,A. S. (1973).[New data on taxonomy of the Steratocephalus Andrassy, 1984 is uncertain. family Teratocephalidae Andrassy (Nematoda)]. Zool. Zh., It seems less appropriate to regard Metateratocephalus 52 : 1768-1776. (In Russian). as a secernentean considering its many presumed ancestral character States. Teratocephalus, on the other hand, GERLACH,S. A. & RIEMANN,F. (1973). The Bremerhaven despite its many assumed derived character States can checklist of aquatic nematodes. Vero& Inst. Meeresforsch. Bremerh. Suppl., 4 : 1-404. neither be easily placed in the Secernentea. According to thescheme proposed by Adamson (1987) they would GOODEY,T. (1963). Soi1 andfieshwater nenzatodes, 2nd ed. rev. both be placed in the Rhabditea. It appears, however, J. B. Goodey. London, Methuen & Co., XVI + 544 p. premature toassign the genera to any higher taxa (order, HOOPER,D. J. (1970). Handling,fiing, staining and mounting subclass or class) based on the present information. nematodes. In : Southey, J. F. (Ed.). Laboratoy methods for To resolve the long-lastingcontroversy over this work with plant and soil nenzatodes. London, Ministry of group, detailed analyses by transmission electron mi- Agriculture, Fisheries and Food, Technic. Bull.no 2 :39-58. croscopy of l) the organization of the anterior sensory INGLIS,W. G. (1983). An outline classification of the phylum structures, 2) theorganization of the cuticle, 3) the Nematoda. Aust. J. Zool., 31 : 243-255.

Revue Nématol. 12 (2) :181-190 (1989) 189 S. Bostrom

LOOF, A.P. A. (1971). Freelivingand plant parasitic nematodes Univ. California Press. London, Cambridge Univ. Press : from Spitzbergen, collectedby Mr. H. van Rossen. Meded. 273-282. LandbHoogesch. Wageningen, 71 : 1-86. POINAR,G. O. Jr. (1983). me natural histoy of nematodes. New LORENZEN,S. (1981). Entwurf eines phylogenetischen Sys- Jersey, Prentice-Hall, 323 p. tems der freilebenden Nematoden.Veros Inst. Meeresforsch. SOHLENIUS,B. (1979). A carbon budget for nematodes, rotifers Bremerh. Suppl., 7 : 1-472. and tardigrades in a Swedish coniferous forest Holarctic soil. LORENZEN,S. (1983).Phylogenetic systematics : Problems, Ecol., 2 : 30-40. achievements andits application to the Nematoda. In : WRIGHT,K. A. & HOPE,W. D. (1968). Elaborations of the Stone, A. R., Platt, H. M. & Khalil, L. F. (Eds). Concepts cuticle of Acanthonchus duplicatus Wieser, 1959 (Nema- in nematode systematiw: London,New York & Paris, toda : Cyatholaimidae)as revealed by light and electron Academic Press : 11-23. microscopy. Can. J. Zool., 46 : 1005-1011. MAGGENTI, A. R. (1963). Comparative morphology in nemic ZELL,H. (1986). Nematoden eines Buchenwaldbodens. 7. Die phylogeny. In : Dougherty, E. C. (Ed.). me lower Metazou Teratocephaliden (Nematoda, Rhabditida). Carolinea, 44 : comparative biology andphylogeny. Berkeley & Los Angeles, 119-128.

Accepté pour publication le 11 juillet 1988.

190 Revue Nématol. 12 (2) :181-190 (1989)