Cheliplana uruguayensis, 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 : 12-15

Cheliplana uruguayensis n.sp.

( Fig. 5 )

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: flat beach further away from the mouth of the canal, sand with organic material a couple of meters from a small intertidal pool (01/08/2004): type locality.

Material. Observations on a live animal. Three whole mounts, one of which designated holotype ( SMNH 7497), another one designated paratype (HU no. 406). Six serially-sectioned specimens, two of which designated paratypes (HU no. 407–408).

Etymology. The species name refers to its occurrence in Uruguay.

Description. The body length of the animal varies between 0.6–0.8 mm. Habitus and internal organisation as in Cheliplana triductibus n.sp., except for the construction of the genital system.

From the testis two morphologically dissimilar vasa deferentia depart. One is of the normal construction; thin-walled and distally widening to a seminal vesicle, which is lined with a membranous, nucleated epithelium. The other vas deferens is enlarged and is surrounded by a layer of very thick, longitudinal muscles. It is 190–260 μm long. The seminal vesicle and the modified vas deferens join each other distally to form the ejaculatory duct, which enters the copulatory bulb. The copulatory organ is of the conjuncta-duplex type, as in the other species of Cheliplana de Beauchamp, 1927. The prostate vesicle is 120–170 μm long, with a diameter of ± 35 μm, and is surrounded by strongly-developed longitudinal muscles. The prostate secretion and the ejaculatory duct distally enter a short, tubular stylet. This stylet is ± 11 μm long.

The male genital atrium is lined with a membranous epithelium and surrounded by a longitudinal muscle layer. In its distal half, it receives a bundle of basophilic glands. Distally it widens before entering the common genital atrium. This common genital atrium is very broad and relatively long. Proximally it receives some eosinophilic and basophilic glands. The epithelium is high and the common genital atrium is surrounded by longitudinal muscles over its entire length. Distally, it narrows again to broaden a second time just before it reaches the gonopore. This is situated at 80% and surrounded by a sphincter.

The ovary is situated dorsally at the left-hand side and joins the bursa. Proximally it is connected with the vitellarium to form an ovovitellarium. This vitellarium bends from the ovary to the ventral side and extends rostrally up to the level of the testis. The caudally-situated female bursa is connected to the ovary by a broad duct consisting of bursal tissue. A separate spermatic duct was not observed. The bursa contains numerous optically-clear vacuoles. An external vagina is connected to the bursa and has a thick, sclerotized wall. It widens to a spherical space just proximally from the vaginal opening. The vaginal opening is situated rostrally from the gonopore. At the place where the external vagina enters the bursa, a separate seminal receptacle is also connected to the bursa. This seminal receptacle is elliptical and is surrounded by circular muscles.

Discussion. These two new species can easily be recognized as species of Karkinorhynchidae , as they have a proboscis provided with symmetrical hooks. In representatives of Diascorhynchidae Meixner, 1929 , the only other schizorhynch taxon with representatives with armed probosces, the hooks are asymmetrical. A large number of diagnostic features makes it easy to place both new species within the taxon Cheliplaninae (see Karling 1983): presence of a postrostral bulb, presence of only one pair of hooks (also the case in some Karkinorhynchinae ), absence of separate lateral glands, lack of eyes (also the case in very few species of Karkinorhynchinae ), presence of a single girdle of adhesive papillae (two such girdles in almost all Karkinorhynchinae ), anteriorly-situated pharynx mostly cylindrical, directed anteriorly and often with a long, spiny prepharyngeal cavity.

By comparing the features of the two species discussed here with the diagnoses of the genera of the taxon Cheliplaninae , the Uruguayan species clearly belong to the genus Cheliplana because of the following features: proboscis hooks without denticles, soft fingerlike side pieces and a cylindrical pharynx with a long spinous cavity. They distinguish themselves from species of Baltoplana Karling, 1949 by the fact that Baltoplana has paired ovaries and testes, and from species of Cheliplanilla Meixner, 1938 because this taxon has crutch-shaped cuticular rods between the proboscis side pieces, proboscis hooks with two pairs of inside denticles, a blind seminal vesicle and an oviform pharynx with a short unarmed cavity (see Karling 1983). They also differ from Archipelagoplana triplocirro Noldt & Hoxhold, 1984 because this species lacks a long spinous pharynx cavity and because A. triplocirro has two small accessory cirri (see Noldt & Hoxhold 1984). Karling (1983) considered the number of testes as an unreliable generic character and by consequence placed all representatives of the genus Rhinipera Meixner, 1928 (one testis) within the genus Cheliplana (two testes), a view we follow here.

Cheliplana triductibus n.sp. stands unique within the genus because of the combined presence of three sclerotized spermatic ducts and one smaller accessory cirrus. In C. hiemalis Brunet, 1968 , C. pacifica Noldt & Hoxhold, 1984 , C. piriformis Brunet, 1968 , C. pusilla Brunet, 1968 , C. schilkei Noldt, 1989 and C. targa ( Marcus, 1952) Karling, 1983 , there is only one sclerotized spermatic duct between the bursa copulatrix and the ovary (see Brunet 1968; Karling 1983; Noldt & Hoxhold 1984, Noldt 1989). C. varicauda Brunet, 1971 has a comparable female and male system to C. triductibus n.sp., but its three spermatic ducts are only slightly sclerotized and the muscular proximal parts contain a spherical nucleus. In the male system, C. varicauda lacks the smaller accessory cirrus. Also the extremely long caudal part, posterior to the genital system, is lacking in the new species (see Brunet 1971). Accessory cirri are also present in C. textilis Jouk & De Vocht, 1989 , but they have two blind accessory cirri that are lined with small spines in the posterior part and even on one side (see Jouk & De Vocht 1989). Only very recently, Ax (2008) described a new species of Cheliplana from brackish water habitats along the French Atlantic coast and the Baltic Sea, with a very similar copulatory organ. This species, C. deverticula Ax, 2008 , has also a winding prostate vesicle and ejaculatory duct, and a slender, armed cirrus (75 μm long) with a single small, armed accessory cirrus (17 μm long). However, nothing is known about the female system of this species. Awaiting more material of C. deverticula and a description of its female system, the Uruguayan specimens are provisionally placed within a new species. If the female system would prove to be identical, C. triductibus n.sp. should be synonymized with C. deverticula .

Cheliplana uruguayensis n.sp. differs from all other species of Cheliplana by the presence of two different seminal vesicles, a character shared with the genus Cheliplanilla , although in the latter the modified seminal vesicle ends blindly. This new species mostly resembles C. targa . Similarities are found in the female system as well as in the male genital system: one testis situated ventrally from the pharynx; a seminal vesicle with a well-developed muscular wall; a very muscular prostate vesicle that distally ends in a short, tubular stylet, and a syncytial bursa containing vacuoles. In contrast to C. targa , which has only one seminal vesicle, C. uruguayensis n.sp. has two seminal vesicles. Moreover, C. uruguayensis n.sp. differs from C. targa by having a non-muscular vas deferens, eosinophilic and basophilic glands opening into the common genital atrium, and by lacking a slerotized spermatic duct.

Diagnosis. Cheliplana triductibus n.sp.: species of Cheliplana with unpaired male and female gonads. Proboscis 30 μ m long and consisting of 11 μ m-long proboscis hooks, 19 μ m-long proboscis halves and a 20 μ m-long postrostral bulb. Without accessory denticles in the proboscis. Two seminal vesicles. Muscular prostate vesicle followed by a 64 μ m-long cirrus with uniform teeth (3–4 μ m long). Small, armed, lateral accessory cirrus with a length of 15 μ m at the distal end of the cirrus. Short female duct. Vagina externa connected with a syncytial bursa. Three cuticularized spermatic ducts and muscular ducts connect the ovary with the bursa.

Diagnosis. Cheliplana uruguayensis n.sp.: species of Cheliplana with unpaired male and female gonads. Proboscis 23 μ m long, consisting of 8 μ m-long proboscis hooks, 16 μ m-long proboscis halves and a 23–25 μ m-long postrostral bulb. Accessory denticles absent in the proboscis. Two different seminal vesicles, of which one is a modified vas deferens surrounded by strongly-developed, longitudinal muscles. Both seminal vesicles are connected with the testis. Long, longitudinally muscular prostate vesicle (± 150 μ m long). Short tubular stylet (11 μ m long). Vagina externa with cuticularized wall connected with a syncytial bursa containing vacuoles. Elliptic seminal receptacle filled with spermatozoa.

Figures

FIGURE 5. Cheliplana uruguayensis n. sp. (A) Habitus of a live animal. (B) Reconstruction of the entire animal.