Polycystis elsae, 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 : 23-24

Polycystis elsae n. sp.

( Fig. 6 C)

Localities in the Indian Ocean. Réunion: Sabine-les-Bains, Cap des Trois Bassins, southern part of the cape, Sargassum from the low eulittoral (02/11/1992) (type locality).

Material. Six animals studied alive and whole mounted, eight specimens serially sectioned. One of the whole mounted specimens designated holotype ( SMNH, no. 7452), the others paratype (HU, nos. 366-370).

Etymology. Dedicated to TA’s cousin, Els Van Ballaer.

Description. Habitus and internal organisation are identical to those of P. naegelii Kölliker, 1845 as described by Karling (1956). It is about 1mm long, with two eyes, and sparsely pigmented. The typical features of the genus as given by Artois & Schockaert (1998) can easily be recognised in the live animals as well as in the sectioned specimens: there is an obvious asymmetrical muscular bulb on the bursal stalk, a small female bursa between both ovaries, a prostate stylet type I that is rather short, and accessory glands type I that enter the male atrium ventrally. The double-walled prostate stylet is 17–23 µm high (= 21; n = 6). Distally the funnel widens and forms a relatively large collar, which, at one side, projects widely beyond the stylet proper. This collar is 14–17 µm broad (= 15; n = 5, the distal part of the stylet in one specimen is oriented in a way that prevents correct measurements) and has no slit. Its distal rim is only partly provided with delicate teeth.

Diagnosis. Species of Polycystis Kölliker, 1845 that is sparsely pigmented. Stalk of male bursa with an asymmetrical muscle bulb. Stylet broad and short, with an asymmetrical distal part forming a collar without a slit. Distal rim only partly serrated with delicate teeth. Distal rim not folded back. Stylet without a spur or hook. Stylet ca 21 µm long; with the collar ca 15 µm broad.

Discussion. At present, the taxon Polycystis includes seven valid species: P. naegelii Kölliker, 1845 , P. hamata Karling, 1986 , P. orientalis Evdonin, 1968 , P. gabriellae ( Marcus, 1948) Karling, 1952 , P. a l i, P. australis Willems et al., 2006 and P. e l s a e n. sp. . P. ali is known in three different forms ( Karling 1986): forms ‘Somali’, ‘California’ and ‘Galapagos’. The specimens from Africa all belong to the form ‘Somali’. However, the clear and consistent differences observed in the construction of the stylet, together with their disjunct distribution indicate that these three forms are better considered separate species. Karling (1986) based his description of P. a l i form ‘Galapagos’ on some photographs, and the dimensions of the stylet seem to be almost the same as in the Somali population. The differences in stylet construction between the two forms are also rather subtle, and should be checked on new material from the Galapagos when it becomes available. Until that time, we refrain from formally naming the Galapagos form as a species. By comparing the specimens of f. ‘California’ and f. ‘Somali’, several consistent morphological differences between them can be found (see Karling 1986). Form ‘Somali’ is always very dark, densely pigmented, while form ‘California’ is colourless or weakly pigmented. There are also distinct differences in shape and length of the prostate stylet type I. The stylet of f. ‘ California’ shows a large slit in its collar, which is absent in f. ‘Somali’. Moreover, the collar of f. ‘California’ is not backfolded as is the case in f. ‘Somali’. Another typical feature of f. ‘ California’ is the fact that the edge of the collar is coarsely toothed over its whole length (finely toothed in f. ‘Somali’). Finally, the stylet of f. ‘ California’ is almost twice as long as that of f. ‘Somali’: 40 µm high and 50 µm wide in f. ‘ California’, while in f. ‘ Somali’ it is 17 µm high and 28 µm broad (see Karling 1986; Schockaert 1982). Karling based his f. ‘Somali’ on the type material of P. a l i and thus this form is P. a l i Schockaert, 1982, while f. ‘California’ is a new species: P. californica n. sp. One whole mount is designated holotype of this new species (SMNH, no. 7453). This holotype is the specimen depicted by Karling (1986, Fig. 75 & Fig. 81). The type locality of P. californica is California ( USA), Pacific Grove, shell gravel and stones taken at low tide from the bay in front of the laboratory (26/03/1969).

The asymmetry in the construction of the stylet of P. e l s a e, with the collar extending at one side of the stylet, is typical of this species. A more-or-less comparable situation is found in P. californica , but far less pronounced. In the latter species, large teeth are present along the entire distal rim of the collar. Moreover, the collar shows a large slit (see Karling 1986). Both features are not found in P. elsae , where the collar only shows delicate teeth on a part of the distal rim. The stylet is also much smaller in P. e l s a e: only ± 40 µm long by ± 50 µm broad.

Diagnosis of P. californica n. sp. See the diagnosis given by Karling (1986) for P. a l i f. ‘California’.

Figures

FIGURE 6. Polycystis ali Schockaert, 1982 A, Prostate stylet type I, side view (from a specimen from Kenya). B, Prostate stylet type I, view from below (from a specimen from Kenya). Polycystis elsae n. sp. C, Prostate stylet type I (from the holotype).