Austrorhynchus kerguelensis Artois & Tessens, 2008, n. sp.

Austrorhynchus kerguelensis n. sp.

(Fig. 1)

Localities in the Indian Ocean. Port Couvreux (Kerguelen) on filiform green algae from the mid eulittoral in a small inlet (25/11/1992) (type locality).

Material. One animal studied alive and whole mounted, designated holotype (SMNH, no. 7442).

Etymology. Named after the islands where it was found (Kerguelen).

Description. The animals are 0,6 mm long (measured on the whole mount) and colourless, with two eyes. The internal organisation as seen on the living animal is identical to that of Austrorhynchus pectatus Karling, 1952.

The prostate stylet type II (Fig. 1 A) is double-walled, with the inner stylet restricted to the tubiform part of the outer stylet. The tube is slightly curved and is more or less of the same length as the funnel. The stylet is 61 µm long. At the transition between tube and funnel, a 19 µm-long hook is connected to the outer stylet. The prostate stylet type III (Fig. 1 B) has a pronounced style and foot (terminology of Karling 1977), which are connected to each other by a narrow clasp, and a transverse comb, with a concave edge with relatively large teeth. The rather short flagellum has teeth along one side over the whole of its length, except for its most distal tip. Measured axially from the proximal end of the foot to the distal end of the flagellum, the stylet is 108 µm long. The plate is 60 µm at its broadest.

Diagnosis. Species of Austrorhynchus Karling, 1952 with two eyes. Prostate stylet type II ca 61 µm long, slightly curved. With ca 19 µm long hook. Inner stylet restricted to the distal, tubiform part of the outer stylet. Prostate stylet type III ca 108 µm long, ca 60 µm broad at its broadest, with pronounced style and foot, connected to each other by a clasp and a broader transverse comb with a concave distal edge with coarse teeth. Flagellum of prostate stylet type III rather short, with comb.

Discussion. Following Karling’s (1977) division of the taxon Austrorhynchus Karling, 1952 into morphological groups, A. kerguelensis can clearly be placed in the pectatus -group. Members of this group all have a prostate stylet type III (the A-organ of Karling 1977) that has a well-differentiated plate with distinct style and foot and with a more or less transverse comb, probably all plesiomorphies (Karling 1977). A. kerguelensis is almost unique within the group, as the combed edge of the plate is clearly concave, where in other species it is clearly convex. Only in A. maldivarum Karling, 1977 does the A-organ also have a concave-edged plate. In that species however, the plate is very narrow and more delicate than it is in A. kerguelensis. The hook of the prostate stylet type II is rather short (much shorter than the tube); in the other species of the pectatus -group the hook is mostly almost as long as the tube. A. kerguelensis is the first species of Austrorhynchus to be found in the subantarctic region of the Indian Ocean.