Uncinorhynchus linusi Willems & Artois

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 : 445-446

Uncinorhynchus linusi Willems & Artois n. sp.

( Fig. 2 E–H)

Locality. iSimangaliso Wetland Park , Lake St. Lucia estuary, detritus-rich, fine-grained sand taken from the land side of a sandbank that cuts off the estuary from the Indian Ocean, December 16, 2009 (type locality).

Material. One animal studied alive and whole mounted, designated holotype (SMNH, Type-8853).

Etymology. Species dedicated to Linus Willems, the first author’s son.

Diagnosis. Unpigmented species of Uncinorhynchus , lacking eyes; proboscis hooks ± 37 µm high with basal wings ± 33 µm long and a dagger-like hook; complex male hard part consisting of a 30 µm-long, hollow stylet, attached to a 35 µm-long, club-shaped plate and an 18 µm-long, spine-like projection.

Description. Habitus and general organisation are almost identical to those of other species of Uncinorhynchus Karling, 1947 (see Karling 1947, 1989; Brunet 1973b).

The rather slender animal is mainly colourless with a brownish intestine, and lacks eyes. It is 1.7 mm long (measured on a whole-mounted specimen). The pharynx is situated almost at midbody. The proboscis is approximately 1/10 of the body length long and carries two proboscis hooks ( Fig. 2 E: h, 2F), which are 36–38 µm high, each with two 29–37-µm-long basal wings and a rather straight, dagger-like hook. Testis and ovary unpaired; a vitellarium could not be observed. The prostate vesicle is elongated and somewhat pear-shaped. It encloses the prostate glands, which have clearly-visible extracapsular parts, and a small internal seminal vesicle. Proximally, this internal seminal vesicle is connected to a large, external seminal vesicle. Distally, the prostate vesicle is connected to a complex hard part ( Fig. 2 E: pst, 2G–H), which consists of the hollow stylet, a spine-like projection (x in Fig. 2 G) and a club-shaped plate (y in Fig. 2 G). The stylet proper is 30 µm long and has a cup-shaped, 12 - µm-wide proximal part and a curved and slender distal part. At the convex side of the cup-shaped part, the stylet carries a perpendicularly-bent, spine-like projection, which is 18 µm long. Additionally, the proximal part of the stylet also carries a 35 µm-long, bent, plate-like part, which is very slender proximally with a distal rectangular part, giving it the overall appearance of a golf club.

Discussion. Species of Uncinorhynchus are characterised by the typical shape of their proboscis hooks, the absence of eyes, a hook-shaped stylet and the absence of a bursal organ in the female genital system ( Karling 1947, 1952, 1989; Brunet 1973b; Kolasa 1977; Willems et al. 2007). At present, seven species are known, which can be distinguished from each other by the detailed structure of the stylet. Whereas the stylet is triangular in shape without any attached processes in U. flavidus Karling, 1947 , U. karlingi Kolasa, 1977 and U. vorago Willems et al., 2007 , it is funnel-shaped and carries a plate-like part in U. hamatus Brunet, 1973 , U. pacificus Karling, 1989 , U. proporus Brunet, 1973 , U. westbladi Karling, 1952 , and the new South African species. However, in U. linusi n. sp. this plate-like extension is only slightly curved, ends bluntly and is attached to the concave side of the stylet, whereas in the other four species the extension is spine-like, bent perpendicularly, has a sharp distal point and is attached to the convex side of the stylet. In addition, the stylet of U. linusi n. sp. carries a second, club-shaped projection, which is missing in all other 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).