Cheliplana remanei ( Meixner, 1928 ) Karling, 1983

Gobert, Stefan, Diez, Yander L., Monnens, Marlies, Reygel, Patrick, Van Steenkiste, Niels W. L., Leander, Brian S. & Artois, Tom, 2021, A revision of the genus Cheliplana de Beauchamp, 1927 (Rhabdocoela: Schizorhynchia), with the description of six new species, Zootaxa 4970 (3), pp. 453-494 : 478-479

Cheliplana remanei ( Meixner, 1928) Karling, 1983

Fig. 8A–B

Synonyms. Rhinepera remanei Meixner, 1928 .

Material examined. New material. GERMANY • 2 whole mounts; Sylt , beach south of List harbour; 55°00’55”N, 6°26’11”E; 28 Apr. 2015; spot with algae and somewhat coarser sediment than the surrounding silt; HU X.2.41– X.2.42 .

Note. No reference material was available to us at the time of this study

Known distribution. Strander Bay, Germany ( Meixner 1928). Kiel Bay, Germany ( Meixner 1928; Schmidt 1972). Sylt, Germany ( Hellwig 1987; Scherer 1985; Noldt 1989). Römö, Denmark ( Schilke 1970). Eastern Scheldt, the Netherlands ( Martens & Schockaert 1981).

Remarks. Meixner (1928) reports an average body length of 0.72 mm, measured on multiple fixed specimens. Live specimens are colourless.A single, continuous caudal haptic girdle is present subterminally.The small proboscis is armed with a pair of smooth, curved hooks, measuring ~18 μm ( Meixner 1928) (17–21 μm in our specimens). A pair of soft proboscis sidepieces has been reported, projecting from the base of the muscular hook supports and bearing a 10–12-µm-long bristle ( Meixner 1928; Noldt 1989). We did not observe the sidepieces in the newly collected material. The postrostral bulb measures approximately three times the length of the proboscis.

The cylindrical pharynx is situated in the anterior third of the body and connected to the mouth via a long prepharyngeal cavity. The interior surface of the prepharyngeal cavity is lined with 4–7 μm-long sclerotised spines, organised in 5 longitudinal rows according to Meixner (1928). Noldt (1989) counted 8–10 rows of spines, measuring 8–11 μm. We were unable to count the spine rows in the newly collected specimens.

A single, large testis is situated alongside the posterior end of the pharynx. An unpaired seminal vesicle enters the proximal end of the copulatory bulb (cb, vs, Fig. 8B ). The bulb is entirely packed with parenchymatic tissue ( Noldt 1989) and surrounded by a layer of longitudinal muscles. A prostatic vesicle is present in the proximal part of the bulb (vg, Fig. 8B ), surrounding the ejaculatory duct. According to Noldt (1989), the prostatic glands empty into the ejaculatory duct near the base of the cirrus. The cirrus is curved and consists of a short, proximal, unarmed, ring-like region (10–12 μm long according to Noldt (1989); 10–21 μm in our specimens, n = 2), followed by a curved, asymmetrical part, armed with bristle-like spines (85–110 μm long according to Noldt (1989); 118–142 μm in our specimens, n = 2) (ci, Fig. 8A–B ). The spines are maximally 9 μm long. At the distal end, the cirrus is unarmed and partially everted to form a sclerotised penis papilla that protrudes into the male atrium (pp, Fig. 8A–B ). In the newly collected specimens from Sylt, the penis papilla measures 20–34 μm (n = 2), though this length likely depends on the contraction state of the copulatory apparatus. Noldt (1989) reports a diameter of 18–25 μm for the penis papilla.

Noldt (1989) presents no information on the female genital tract. In our specimens, a single large ovary is visible posterior to the male copulatory bulb. A bursa lies adjacent to the ovary. No vagina (interna or externa) or spermatic duct between the bursa and ovary was observed.

Figures

FIGURE 8. A–B. Cheliplana remanei (Meixner, 1928) Karling, 1983 from Sylt, Germany. A. Camera lucida drawing of the cirrus. B. Drawing of the copulatory bulb, including cirrus and seminal vesicle. C–D. Cheliplana terminalis Brunet, 1968. C. Camera lucida drawing of the cirrus. D. Photograph of the distal end of the cirrus showing the sclerotised penis papilla. Scale bars: A, C = 50 μm; B = 100 μm; D = 20 μm.