Prognathorhynchus

Willems, Wim R., Reygel, Patrick, Steenkiste, Niels Van, Tessens, Bart & Artois, Tom J., 2017, Kalyptorhynchia (Platyhelminthes: Rhabdocoela) from KwaZulu-Natal (South Africa), with the description of six new species, Zootaxa 4242 (3), pp. 441-466 : 444

Prognathorhynchus spec.

( Fig. 2 A–D)

Locality. iSimangaliso Wetland Park , Eastern Shores, Mission Rocks (28°16’50.1’’S, 32°29’06.3’’E), sand and shrubby red algae from rock pool in the mid-eulittoral of a highly-exposed tidal area with sandstone terrace covered with invertebrates (barnacles, mussels, limpets, corals, tunicates), December 5, 2009.

Material. One animal studied alive and whole mounted (HU, no. VII.3.42).

Description and remarks. Rather small (0.5 mm measured on whole-mounted specimen) and slender, colourless animals with two eyes and prominent caudal glands. The globular proboscis measures approximately 1/ 10 of the total body length and carries two proboscis hooks ( Fig. 2 B: h, 2D). These hooks are 19–20 µm long and each consists of a small, distal sharp-ending part, and a wider, plate-like base that is 19 µm wide at its broadest point. In between both parts of each hook, two very thin projections pointing sideways are present. The opening of the proboscis cavity is surrounded by sensory bristles. The pharynx is situated midbody and has a diameter of approximately 1/6 of the body. Testis and ovary are unpaired, situated in the first and last third of the body respectively. A vitellarium could not be observed. The single individual is clearly infected by an apicomplexan parasite (see Fig. 2 B: x). The testis is rather small, with few sperm and the seminal vesicle is clearly empty and therefore hard to discern. The tubiform stylet ( Fig. 2 B: pst, 2C) is 14 µm long and 5 µm wide proximally. It is shaped like a pipe with a short proximal part and a longer, straight distal part, both parts forming a right angle with a very short projection on the convex side.

Based on the general organisation and the structure of both the stylet and the proboscis hooks, this species clearly belongs to the taxon Prognathorhynchus Meixner, 1929 . At present, this taxon contains 11 valid species, of which the stylets of Prognatorhynchus busheki Ax, 1997 and P. eurytuba Ax & Armonies, 1987 and to a lesser degree those of P. dividibulbosus Ax & Armonies, 1990 , P. dubius Meixner, 1929 , P. kurilensis Evdonin, 1972 , P. lacteus Evdonin, 1971 and P. parvulus Brunet, 1973 are similar in shape to that of the South African specimen. However, the stylet is between two (in P. parvulus ) and ten times (in P. lacteus ) longer in these species ( Ax 1952, 1997; Evdonin 1971, 1972, 1977; Brunet 1973b; Ax & Armonies 1987, 1990; Reygel et al. 2011). Since only one specimen was studied, which was furthermore infected by a parasite, which could have affected the development of the male system as it is far less developed than the female system, we refrain from formally identifying it or describing it as a new species.

Figures

FIGURE 2. Prognathorhynchus spec. A. Habitus of free-swimming animal. B. General organisation (from a live specimen). C. Stylet. D. Proboscis hook. Uncinorhynchus linusi n. sp. E. General organisation (from a live specimen). F. Proboscis hooks. G – H. Stylet. (F – H from the holotype).