Coronhelmis mimosa, 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 : 26-27

Coronhelmis mimosa n.sp.

( Figs. 11 A–11B)

Locality. Playa la Moza, Parque Nacional de Santa Teresa, Departamento de Rocha, Uruguay (33°58’30.02”S, 53°31’50.89”W). Beach north of the observation tower: coarse sand near the stairs at about 8 m from the rocks (24/07/2004): type locality.

Material. Observations on a live animal. Four whole mounts, one designated as the holotype ( SMNH 7502) and one designated paratype (HU no. 420), two of poor quality.

Etymology. The species name refers to the opening and closing movements of the stylet as observed on the live animal. These movements are reminiscent of those of the leaves of the plant genus Mimosa .

Description. The animal is ± 0.5–0.6 mm long. The pharynx lies in the middle of the body. The general organisation of the genital system (based on observations on a live animal) does not differ from other species of the genus Coronhelmis Luther, 1948 (see Ax 1951, 1994; Ehlers 1974; Luther 1948).

The stylet is 15–17 μm long (m = 16 µm; n = 3) and 12–15 μm (m = 14 µm; n = 3) broad. It consists of a proximal, thin-walled, 7–9 μm-long part [called “Manschette” by Luther (1948)] and a distal ring of 4–5 μmlong spines. The proximal part has a number of grooves of ± 4 μm long that run lengthways. In the central part of the stylet of one of the whole mounts, a reticulate structure was observed, possibly caused by the unevenness of the stylet wall. In the live animals, we observed opening and closing movements of the ring of spines.

Discussion. This species has all diagnostic characters of the genus Coronhelmis (see Luther 1948): the presence of a bursa copulatrix and a copulatory organ with a stylet that consists of a proximal part or “Manschette” and a distal ring of spines. An overview of the diagnostic characters of all species described was given by Willems et al. (2005b: table 1).

From this table it is immediately clear that Coronhelmis mimosa n.sp. is a relatively small species of Coronhelmis , of which the representatives are normally around 1 mm long. In C. mimosa , the ratio “Manschette” to entire stylet length is ± 1/2. Only in C. cuypersi Willems et al., 2005 , C. lutheri Ax, 1951 , C. novaecaledoniae Willems et al., 2005 and C. subtilis Ax, 2008 , is a comparable ratio found. Of these four species, the stylets of C. cuypersi , C. lutheri and C. subtilis have more than 30 spines. The number of spines in Coronhelmis mimosa could not be ascertained, but presumably amounts to 10–15, a number comparable to that found in C. novaecaledoniae . However, the stylet is proportionally much wider in C. novaecaledoniae (width/length = 1.5) than in C. mimosa (width/length = 0.9). The proximal grooves and the central, reticulate structure can not with certainty be considered part of the stylet, but are not mentioned in other species. Because of the above-cited differences from the other species of the genus Coronhelmis , the Uruguayan specimens are considered to belong to a new species.

Unfortunately, the whole mount with the reticulate structure in the central part of the stylet was not well conserved. Another whole mount was chosen as the holotype.

Diagnosis. Coronhelmis mimosa n.sp.: small species of Coronhelmis with a 15–17 μ m-long and 12–15 μ m-broad stylet that consists of a proximal “Manschette” with a length of 7–9 μ m and a distal ring of 4–5 μ m-long spines. Possibly vertical grooves in the proximal part and a reticulate structure in the central part.

Figures

FIGURE 11. Coronhelmis mimosa n. sp. (A) Habitus of live animal. (B) Stylet (right one from holotype). Byrsophlebs caligulachaena (Ehlers & Ehlers, 1981) Karling, 1985 (C) Habitus of live animal. Ceratopera axi (Riedl, 1954) Den Hartog, 1964 (D) Bursal appendage. (E) Stylet.