Nematoda: Cystidicolidae) of Sturgeons

Article available at http://www.parasite-journal.org or http://dx.doi.org/10.1051/parasite/1996032169 S o m e n e w d a ta o n th e m o r p h o l o g y o f S p in it e c t u s in e r m is (N e m a t o d a : C ystidicolidae ), a r a r e p a r a s it e o f e e l s , AS REVEALED BY SEM MORAVEC F.* Summary : Résumé : D onnées nouvelles sur la morphologie en microscopie électronique à balayage de Spinitectus inermis ( N ematoda: Scanning electron microscopy studies of two males of Spinitectus Cystidicolidae), parasite peu fréquent de l'anguille inermis (Zeder, 1800), a stomach parasite of eels, Anguilla anguilla (L.), in Europe made it possible to describe in detail the L'etude en microscopie électronique à balayage de deux mâles de apical structure of this rare nematode as well as the morphology Spinitectus inermis (Zeder, 1800), parasite digestif de l'anguille, of the male caudal end. The structure of the mouth of S. inermis is Anguilla anguilla (L.) en Europe, a permis de détailler la structure intermediate between those of freshwater and marine species as apicale de ce nématode rare, ainsi que la morphologie de regards the configuration of the pseudolabia and the presence of l'extrémité caudale du mâle. La structure de la partie buccale de sublabia. This is probably associated with the host which occurs in S. inermis se situe entre celles des espèces de mer et d'eau both habitats. The presence of a median, unpaired preanal douce, pour ce qui concerne la configuration des pseudolabia et papilla is reported in the male of S. inermis for the first time. la présence de sublabia. Ceci est probablement lié à la présence de l'hôte dans les deux habitats. Pour la première fois, l'existence KEY WORDS : nematode, parasite, morphology. Spinitectus, Anguilla, d'une papille médiane préanale est signalée chez le mâle de MOTS CLÉS : Spinitectus, nématode, parasite, Anguilla, morphologie. S. inermis. INTRODUCTION____________________________ (Jilek and Crites, 1982; Petter and Morand, 1988; De, 1988). Nevertheless, these studies show that there may be, for example, distinct differences in the structure of pinitectus inermis (Zeder, 1800) is a rare, spe the mouth among the Spinitectus species. S. inerm is cific nematode of the stomach of eels, A nguilla has not so far been studied by SEM. In this paper the an g u illa (L.) in Europe, where it is widespread results of a SEM study of S. in erm is are presented. Sin the North, Baltic and Mediterranean Seas basins (Moravec, 1994). Although this species was known to helminthologists as early as at the beginning of the last century, the knowledge of its morphology remained MATERIALS AND M ETHODS________________ poor for a long time due to its rare occurrence. A detailed redescription of S. inermis, based on light wo male specimens of S. inerm is from the col microscopical study, was provided only by Moravec lection of the Institute of Parasitology, Academy (1979). However, some taxonomically important fea of Sciences of the Czech Republic, were used tures in cystidicolids, especially the structure of the T for SEM study. They were from the material collected mouth, can be properly studied only by using scan from Anguilla anguilla from the Břehyně Brook near ning electron microscopy (SEM). Of many Spinitectus Doksy, northern Bohemia, Czech Republic, on 9th species parasitizing fishes, this method has so far been September 1976 on which Moravec’s (1979) redes used only in six species ( Spinitectus g racilis Ward and cription of S. in erm is was based. Originally these Magath, 1917, Spinitectus carolini Holl, 1928, Spini nematodes were fixed in hot 4 % formaldehyde and, tectus beaveri Overstreet, 1970, Spinitectus micracan- after light microscopical examination, they were stored thus Christian, 1972, Spinitectus jamundensis That in 70 % ethanol. For SEM examination, the nematodes cher and Padilha, 1977, Spinitectus minor De, 1988) were transferred to 4 % formaldehyde, postfixed in 1 % OsO4, dehydrated through graded ethanol and acetone and then subjected to critical point drying. The speci mens were sputter-coated with gold and examined * Institute of Parasitology, Academy of Sciences of the Czech Repu blic, Branišovská 31, 370 05 České Budějovice, Czech Republic. with a Tesla BS-300 scanning electron microscope at Tel. : (42-38) 41 158; Fax (42-38) 47 743; E-mail <[email protected]>. an accelerating voltage of 15 kV. Parasite, 1996, 3, 169-174 Mémoire 169 MORAVEC F. RESULTS submedian labia, two subdorsal and two subventral, with broad base (Figs 1B, 2A), forming dorsolateral and dorsoventral margins of the oral opening. A simple, T he SEM examination of the cephalic end of the smooth, narrow, sclerotized structure (“sublabium” two male specimens of S. in erm is shows that according to the terminology of Margolis, 1977), with the oral opening is oval, dorsoventrally elon a somewhat thickened free margin, is attached by its gated, surrounded by four poorly developed, very low base to the inner surface of each labium (Figs 1B, 2A). Fig. 1. - Spinitectus inermis (Zeder, 1800), male; SEM micrographs. A) Anterior end of body, sublateral view; B) subapical view of mouth; C) anterior end, apical view; D) third and fourth rings of cuticular spines, subventral views; e : excretory pore, 1 : submedian labium, p : cephalic papilla, pf : papilla-like formation separating sublabia, μl : pseudolabium, s : sublabium. Scale bars ; A) 50 μm; B) 10 μm; C) 40 μm; D) 20 μm. Parasite, 1996, 3, 169-174 1 7 0 Mémoire Morphology of Srtxmx.Tt s m m m In apical view, each labium gradually narrows towards Ventral precloacal cuticular ridges (area rugosa) are both ends. The separation of both subdorsal and both well developed, and consist of several longitudinal subventral sublabia is very short, but distinct. The rows composed of mostly numerous short, narrow, lon cuticle may form a small papilla-like structure (Fig. 1B) gitudinal cuticular elevations (Fig. 2D, E). At the region separating the right and the left sublabia. The width of the preanal papillae, the cuticular ridges are formed of the sublabia is much greater than their length. only by two distinct subventral longitudinal rows, The lateral pseudolabia (Figs 1B, 2A) are relatively which continue far anteriorly, and by a short median large and project anteriorly beyond the labia. They do row (composed of only three cuticular elevations) not touch each other by their inner margins and are situated in front of the unpaired preanal papilla. A continuous on their inner margin with the lateral ante small, transverse cuticular elevation is present imme rior extensions of the buccal cavity wall. No distinct diately anterior to the unpaired papilla and posterior lateromedian plate, sepatated from the pseudolabium, to the median row of cuticular elevations (Fig. 2B, E). is present. In apical view, the flat inner parts of the Precloacal cuticular ridges extend anteriorly approxi pseudolabia covering partly the oral opening are dor- mately to the level of the proximal end of the invagi- soventrally expanded, forming two (one laterodorsal nated larger (left) spicule. In the region anterior to and one lateroventral) triangular extensions with sharp preanal papillae, longitudinal rows of cuticular ridges corners on each pseudolabium. Inner margins of both are more numerous (6). pseudolabia are dorsoventrally straight, parallel to each other (Figs 1B, 2A). The narrow, inner part of each DISCUSSION pseudolabium continues posteriorly into a thickened pulp bearing two elongate submedian cephalic papillae argolis (1977), De and Moravec (1979), Appy (Figs 1B, 2A) and a small amphid. and Anderson (1982), Ko (1986), Fagerholm Fig. 1A, C shows clearly that in properly extended spe and Berland (1988) and others demonstrated cimens the body wall at the cervical region is that the characters in the structure of the mouth, which somewhat depressed laterally and dorsoventrally, sug are not easily visible with the light microscope, are very gesting four longitudinal sectors, thus being responsible important for the identification and systematics of cys- for the square appearance in apical view (Fig. 1C). tidicolid nematodes. Jilek and Crites (1982) were the The SEM study has shown that the two anteriormost first to study the mouth structure in Spinitectus using rings of cuticular spines are much closer to each other SEM. They found the structure of the mouth of S. b ea- than the following rings, being interrupted on both veri, a parasite of the marine fish Albula vulpes (L.) in sides of the body by lateral lines (Fig. 1A). Each of the Florida, to be considerably different from that of the two anterior rings consists of 48-50 spines in the two three other North American species, S. gracilis, S. caro- male specimens studied. The spines are simple, elon lini and S. micracantbus parasitic in freshwater fishes. gate, sharply pointed and no pore-like openings Petter (1984) compared the apical structures of all the beneath them were observed (Fig. 2C). then known apical structures of Spinitectus spp. (based The excretory pore is situated ventrally just below the on both light and scanning electron microscopy stu fourth ring of spines (Figs 1D, 2C). A spine expected dies) and found that species parasitic in freshwater anterior to the excretory pore is absent (Fig. 2C). Dei- fishes of all continents had well developed pseudolabia rids were not observed. bearing submedian papillae and amphids, whereas The present study confirms that there are ten pairs of those from marine fishes had reduced pseudolabia, caudal papillae in the male, four preanals, one ada- without supporting papillae and amphids. Two species, nals and five postanals. The papillae of the first and Spinitectus agonostomi Moravec and BaruŠ, 1971 and third pairs of preanals, as well as the adanals, are dis Spinitectus pachyuri Petter, 1984, from freshwater tinctly smaller than those of the second and the third fishes belonging to essentially marine families (Mugi- pairs of preanals and, in contrast to the latter, they are lidae and Sciaenidae) had similar apical structures located more laterally (Fig.

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