Carcharodorhynchus viridis, Steenkiste, Niels Van, Volonterio, Odile, Schockaert, Ernest & Artois, Tom, 2008

Steenkiste, Niels Van, Volonterio, Odile, Schockaert, Ernest & Artois, Tom, 2008, Marine Rhabdocoela (Platyhelminthes, Rhabditophora) from Uruguay, with the description of eight new species and two new genera, Zootaxa 1914, pp. 1-33 : 15-16

Carcharodorhynchus viridis n.sp.

( Fig. 6 )

Locality. La Coronilla, Departamento de Rocha, Uruguay (33°54’18.50”S, 53°30’39.30”W). Beach and mouth of the canal near hotel Parque Océanico: sand covered by a thin green layer of organic material and sand with organic material near a small pool in open contact with the ocean (01/08/2004): type locality.

Playa Cerro Chato, Parque Nacional de Santa Teresa, Departamento de Rocha, Uruguay (33°59’6.34”S, 53°31’48.81”W). Coarse superficial sand between rocks (20/07/2004).

Playa las Achiras, Parque Nacional de Santa Teresa, Departamento de Rocha, Uruguay (33°59’5.00”S, 53°31’54.79”W). Sand of a steeply declining beach close to the waterline (26/07/2004).

Material. Observations on a live specimen. Three whole mounts, one of which designated holotype ( SMNH 7498), another one designated paratype (HU no. 409).

Etymology. The species epithet refers to the colour of the live animal. Viridis (Lat.) : green

Description. Carcharodorhynchus viridis n.sp. is 1–1.4 mm long and has a vivid green colour. The animal lacks eyes and adhesive papillae were not observed. The pharynx rosulatus has a diameter of ± 75 μm and is at 65% of the body length. The epidermis contains a large number of elliptical rhabdites with an average length of 2–3 μm, especially at the rostral side. The proboscis is slightly asymmetrical with one half somewhat larger than the other one, and measures 55–71 μm. In all whole mounts, only one field of denticles was observed on the largest proboscis half. However, in one specimen, denticles were also present on the transition from the larger to the smaller proboscis half. The denticles are not in rows, but randomly distributed in an oblong field. All denticles are uniform.

About eight testes were observed in the live animal, although the precise number could not be determined. They are in one row, which extends rostrally from the pharynx. Two seminal vesicles are situated just behind the pharynx. The apparently very muscular copulatory apparatus is 55 μm long and contains at least two different types of prostate secretion. The hard parts of the male copulatory organ consist of a 7 μm-long stylet, surrounding a 12–15 μm-long cirrus. The stylet is an asymmetrical tube, which is distally backfolded to form a second tube that surrounds the distal part of the cirrus. The teeth of the cirrus are spirally-implanted and are longer at the proximal and distal ends. The male genital duct is large and very muscular. The female system could not be observed in the live animal nor in the whole mounts.

Discussion. Based on the general organisation and the morphology of the proboscis, this species can easily be placed within the genus Carcharodorhynchus Meixner, 1938 . All representatives of this genus are slen- der, lack eyes and have a proboscis that is armed with denticles, usuallly in two fields on the sides of the proboscis halves. They have paired gonads (paired ovaries, vitellaria and one to eight pairs of testes). The male copulatory organ has a cirrus or a stylet. Sometimes both structures are present.

The structure and armament of the proboscis are uncertain as reliable diagnostic characters for the different species. Fields of denticles on the sides of both the proboscis halves are present in all species. Consequently two U-shaped batteries of denticles are formed. Sometimes the denticles are placed in rows, sometimes randomly. Only the form, size and density of the denticles can differ distinctly. Thus the observation of only one field of denticles in the whole mounts of the Uruguayan animals probably gives an incomplete picture of the armament of the proboscis, especially because in the live animals fields of denticles were observed on both proboscis halves. Further, the species belonging to this genus can be grouped into a group of species with asymmetrical proboscis halves and species with symmetrical proboscis halves. Also the construction of the male copulatory organs (either a cirrus, a stylet or both) is remarkably similar when the different species are compared. This may suggest that the number of species currently recognised might be reduced after a thorough revision of this genus.

Carcharodorhynchus viridis n.sp. differs from all but one of the other species of this genus by the structure of the male copulatory organ. Together with C. involutus Jouk & De Vocht, 1989 , it is the only species where the stylet surrounds the cirrus (see Jouk & De Vocht 1989). In other species where both a cirrus and a stylet are present, this stylet is always found within the cirrus. C. viridis n.sp. differs from C. involutus because the cirrus is longer than the stylet while in C. involutus the reverse is true.

Diagnosis. Carcharodorhynchus viridis n.sp.: species of Carcharodorhynchus with a bright green colour. Slightly asymmetrical, armed proboscis with a length of 55–71 μ m. A 7 μ m-long stylet consisting of an asymmetrical tube, which distally bends inwards to form a second tube that distally surrounds a 12–15 μ m long cirrus. Spirally-implanted cirrus teeth that are longer distally and proximally.

Figures

FIGURE 6. Carcharodorhynchus viridis n. sp. (A) Habitus of a live animal. (B) Proboscis of two different specimens. (C) Copulatory apparatus with cirrus and stylet (from the holotype).