Paraustrorhynchus neleae, Artois, Tom J. & Tessens, Bart S., 2008

Artois, Tom J. & Tessens, Bart S., 2008, Polycystididae (Rhabditophora: Rhabdocoela: Kalyptorhynchia) from the Indian Ocean, with the description of twelve new species, Zootaxa 1849, pp. 1-27 : 10-11

Paraustrorhynchus neleae n. sp.

( Fig. 2 A–C, H–I)

Localities in the Indian ocean. English Point, Mombasa ( Kenya): at 6 m depth on Thalassia hemprichii , partly covered with the epiphyte Syringodium isoetifolium (09/06/1987) (type locality). Kanamai, Mombasa ( Kenya): flattened red algae from a big tide pool on the reef, ± 1 km south of the institute (15/10/1992). Zanzibar Island ( Tanzania): Mbweni, beach behind the Mbweni Ruins Hotel, north of the creek, in a tide pool with a broad-leafed seagrass (17/08/1995).

Material. Several animals studied alive. Three whole mounts from the type locality; one of them designated holotype ( SMNH, no. 7443), the other two paratype (HU, nos. 353-354). One whole mount from each of the other localities.

Etymology. Named after Nele Spelmans, wife of TA.

Description. The animals are opaque, brown-green pigmented on the dorsal surface, the ventral surface is unpigmented. They are 0,6–0,9 mm long (measured on whole mounts), with two eyes. The proboscis is rather small, only about 1/7 of the body length long. The pharynx is in the first body half and slightly inclined forwards. The gonads are paired. The two testes are rather small and lie at the level of the pharynx. The ovaries are situated in the caudal body end. The vitellaria extend at both sides of the body from the eyes to the rear end of the body. Male and female atrial system as in P. pacificus Karling & Schockaert, 1977 .

There are two hard parts in the proximal part of the male atrium: a prostate stylet type II ( Fig. 2 B) and a prostate stylet type III ( Fig. 2 C). The prostate stylet type II is double-walled. At about its midpoint, it makes a 90° turn, which makes the curved distal part of the stylet run perpendicular to the proximal part. Distally the stylet tapers gradually to end in a sharp point. The inner stylet can be followed almost over the whole length of the outer stylet. Only in the proximal 1/5 is it lacking. At one side, the proximal part of the outer stylet shows a longitudinal slit ( Fig. 2 B, indicated by an arrow), which broadens at the level of the proximal end of the inner stylet, leaving the inner stylet apparently uncovered at this side. The prostate stylet type II is 64–74 µm long (= 71, n = 5). An ovoid prostate vesicle type II is connected to this stylet. It has a very thick muscular wall. The prostate stylet type III ( Fig. 2 C) consists of two long arms, proximally connected to a single broad folded plate. These arms extend from the two proximal corners of the plate, curving towards each other and broadening distally. The distal ends are very broad and are provided with teeth (often very difficult to see on the smallest of the two arms). The muscles surrounding the male atrium form a thick muscular bulb at the proximal end of this stylet. Measurements of the prostate stylet type III (6 specimens): length 24 – 37 µm (= 29); proximal width: 39–42 µm (= 40); width in the middle: 5–9 µm (= 7); distal width 18–39 µm (= 31). Some glands are associated with the prostate stylet type III, probably a prostate vesicle type III. The seminal vesicles are relatively small. The short ejaculatory duct enters the proximal part of the male atrium near to the prostate stylet type III. The male atrium is very broad and muscular. At one side it has a large fold in which large amounts of sperm were observed.

Diagnosis. Species of Paraustrorhynchus Karling & Schockaert, 1977 , with a prostate stylet type II of ca 71 µm long, that makes a 90° turn at about its midpoint. Distal end very sharp. Outer stylet leaves the inner stylet partly uncovered proximally. Prostate stylet type III consisting of a common proximal plate from which two arms depart. Both arms curved towards each other, with broad distal ends showing broad teeth. Prostate stylet type III ca 29 µm long, proximally ca 40 µm, in the middle ca 7 µm and distally ca 31 µm broad. Without female bursa.

Discussion. P. n e l e a e shows all the diagnostic features of the taxon Paraustrorhynchus (see Karling & Schockaert 1977). Only the absence of insemination ducts should be checked on sections, but as the rest of the organisation as observed in living animals and whole mounts is completely as in Paraustrorhynchus , we presume that insemination ducts are indeed lacking in the new species.

Until now, only three species of Paraustrorhynchus were known: P. e l i x u s, P. caligatus Willems et al., 2006 and P. pacificus . In P. e l i x u s the prostate stylet type II is a very small hook, while its prostate stylet type III is clearly bipartite. This is not the case in the three other species, which have a rather long prostate stylet type II and a prostate stylet type III that consists of a common proximal base from which two arms depart. Moreover, in P. elixus a female bursa is present,1 which is lacking in the other three species. All these differences cast some doubts on the relationship between P. e l i x u s and the other species of Paraustrorhynchus (see also Karling & Schockaert 1977), but for the time being, i.e. before a proper cladistical analysis of the entire taxon Polycystididae is carried through, we refrain from splitting the genus.

The fact that the distal half of the prostate stylet type II runs perpendicular to the proximal half clearly distinguishes P. n e l e a e from P. pacificus , where the prostate stylet type II is evenly curved. Moreover stylet type II is almost twice as long in P. pacificus (± 125 µm) as it is in P. neleae (± 71 µm). The prostate stylet type III is very similar in both species, with the two arms widening abruptly distally. The distal rims of both arms are completely serrated in P. neleae . In P. pacificus one of the arms has a completely serrated distal rim, while the other one is somewhat forked, with one small, serrated part and the other one not serrated. Also prostate stylet type III is much larger in P. pacificus (± 140 µm long) than in P. n e l e a e (± 29 µm long).

P. c a l i g a t u s also resembles P. n e l e a e and P. pacificus , but differs from both in that the prostate stylet type II is straight and typically boot-shaped (see Willems et al. 2006b). It is even smaller than in P. neleae (± 49 µm). The prostate stylet type III of this species is very different from that of both P. pacificus and P. neleae as the arms broaden evenly towards their distal ends, giving them the shapes of broad plates (see Willems et al. 2006b). This stylet is a bit larger (± 37 µm long) than it is in P. n e l e a e.

Figures

FIGURE 2. Paraustrorhynchus neleae n. sp. A, Habitus (from a live animal). B, H, Prostate stylet type II (from the holotype). C, I, Prostate stylet type III (from the holotype). P. elixus. D, Prostate stylet type III (from a specimen from Kenya). E, Prostate stylet type II (from the same specimen from Kenya). F, Prostate stylet type III (from a specimen from Brazil). G, Prostate stylet type II (from the same specimen from Brazil). J, Prostate stylet type III (from a specimen from New Caledonia). Arrows explained in the text.