Cheliplana mamkaevi Evdonin, 1977

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 : 474

Cheliplana mamkaevi Evdonin, 1977

Material examined. None.

Known distribution. Putyatin Island, Peter the Great Gulf, Russia ( Evdonin 1977). Kunashir Island, Pacific Coast, Russia ( Evdonin 1977). Kronocka Bay, Kamchatka Peninsula, Russia ( Evdonin 1977). Anadyrsk and Olindorstvik, Bering Strait, Russia ( Evdonin 1977).

Remarks (summarised from literature). Specimens are up to 2.5 mm long. The proboscis is armed with a pair of sclerotised 10–28-µm-long hooks. The proboscis sidepieces are not sclerotised and of the same length as the hook supports. The post-rostral bulb measures approximately twice the length of the hook supports.

The pharynx bears eight tubercles or papillae on its anterior rim. The prepharyngeal tube is armed with numerous small spines. The common genital opening lies at 75%. An unpaired testis is situated dorsal to the prepharyngeal cavity. A pair of seminal vesicles enters the proximal end of the oviform, 100-µm-long copulatory bulb to form an internal seminal vesicle. This internal seminal vesicle bears two blind-ending pockets, which envelop a small prostatic vesicle, containing coarse-grained secretion in the middle part and fine-grained secretion peripherally. Distally, the ejaculatory duct forms a sclerotised, 30–60-µm-long cirrus. The spines of the cirrus measure 10–14 μm proximally and 5–7 μm distally.

A single ovary is situated caudally to the copulatory apparatus. Evdonin (1977) mentions the presence of a vagina interna, which connects to a bursa adjacent to the ovary.

The copulatory apparatus resembles that of C. gemmifera in its general organisation. The short, armed cirrus and the internal seminal vesicle in the copulatory bulb as drawn by Evdonin (1977) are nearly identical to those in C. gemmifera . Noldt (1989) discusses these similarities, but raises a number of differences distinguishing the species, including the different sizes and structures of the copulatory bulb and the presence of a vagina interna in C. mamkaevi . The new specimens of C. gemmifera (see earlier) did not allow study of the female system or detailed observations of the copulatory bulb’s fine structure. Without additional study of the type material or newly collected material, we refrain from synonymizing the two species. Certainly, the similarities between the two species, in particular the properties of the lobed internal seminal vesicle and prostatic glands, are striking and the two species, if indeed distinct, are likely closely related.