Cheliplana longissima, Gobert & Diez & Monnens & Reygel & Van Steenkiste & Leander & Artois, 2021

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 : 463

Cheliplana longissima n. sp. Gobert, Reygel & Artois

Figs. 2F–H , 3D–E

Etymology. The species epithet ‘longissima’ refers to the very long cirrus.

Material examined. Holotype. PANAMA • 1 whole mount; Isla de Taboga , Playa de la Isla Taboga; 8°48’05”N, 79°33’16”W; 9 Dec. 2011; intertidal, medium fine to medium coarse sand from ripple marks in between Caulerpa and close to swash zone; KV.665.

Other material. PANAMA • 3 whole mounts (incl. one juvenile specimen) and 3 serial sections; Isla de Taboga , Playa de la Isla Taboga; 8°48’05”N, 79°33’16”W; 9 Dec. 2011; intertidal, medium fine to medium coarse sand from ripple marks in between Caulerpa and close to swash zone; HU X.2.34–X.2.39 .

Description. Live specimens are transparent to slightly pink in colour.The body is 0.9–1.0 mm long, as measured on squeezed, whole-mounted specimens. A continuous haptic girdle is present at the caudal body-end (ag, Fig. 2H ). The proboscis bears a pair of 15–23-μm-long (x = 19 μm, n = 4), curved hooks (h, Fig. 2G ). The hook supports are relatively small, measuring 9–10 μm (hs, Fig. 2G ). The mouth is situated a short distance behind the proboscis and is connected to the cylindrical pharynx through a long prepharyngeal tube (ph, ppc, Fig. 3E ). The epithelium lining the inside of the tube is differentiated to form long, finger-like papillae lining the entire surface of the tube. These papillae do not appear to be sclerotised. Some diatom frustules were observed in the digestive tract.

The common genital opening is situated in the posterior quarter of the body and is surrounded by glands (gl, gp, Fig. 2H ). Two small, elongate seminal vesicles are provided with longitudinal muscles and enter the copulatory bulb proximally. The copulatory bulb (cb, Figs. 2H ; 3D,E ) is elongate and contains a prostatic vesicle in its proximal third (vg, Figs. 2H ; 3D ), followed distally by a long ejaculatory duct and a long, armed cirrus (ci, Figs. 2F,H ; 3D,E ). A thick layer of longitudinal muscles and circular muscles surrounds the copulatory bulb. The inside wall of the copulatory bulb shows a series of thin transverse crests on the dorsal side of the bulb ( Fig. 2H ). The interior surface is lined with a thin epithelium. The cirrus measures 235–365 μm (x = 300 μm, n = 2) and is armed with very fine spines (ci, Figs. 2F,H ; 3D,E ). In all available specimens, a characteristic loop was observed in the proximal part of the cirrus (ci, Figs. 2F,H ; 3D ). Distally, the cirrus ends in a short, sclerotised penis papilla (pp, Fig. 2F ; 3D ).

The vaginal opening is located terminally and can be closed by a sphincter. It opens into an elongate vagina externa (ve, Fig. 2H ), the distal end of which is surrounded by circular muscles. The vagina externa connects to the bursa, which is not muscular (b, Fig. 2H ). The bursal lumen is lined with a pseudo-cuticular lining and surrounded by a thick, apparently syncytial parenchymatic tissue. The proximal end of the bursa is globular, nearly spherical, and lies adjacent to the single ovary, on the right-hand side of the body (ov, Fig. 2H ). The quality of the sections did not allow study of any further details of the female system, such as a possible connection between the ovary and bursal complex and between the ovary and common genital atrium/gonopore. A number of conspicuous nuclei are present at the proximal end of the bursa ( Fig. 2H ).

Figures

FIGURE 2. A–C. Cheliplana hawaiiensis n. sp. A. Habitus of the live specimen. B. Camera lucida drawing of the proboscis. C. Camera lucida drawing of the sclerotised cirrus. D–E. Cheliplana mauii n. sp. D. Camera lucida drawing of the proboscis. E. Camera lucida drawing of the sclerotised cirrus. F–H. Cheliplana longissima n. sp. F. Camera lucida drawing of the sclerotised cirrus and penile papilla. G. Camera lucida drawing of the proboscis. H. Reconstruction from the left-hand side of the male and female genital organs in the posterior part of the body. Scale bars: B-D, G = 20 μm; E = 10 μm; F = 50 μm.

FIGURE 3. A–C. Cheliplana hawaiiensis n. sp. from Hawaii. A. Photograph of a live specimen. B. Photograph of the proboscis. C. Photograph of the cirrus. D–E. Cheliplana longissima n. sp. D. Photograph of a live specimen. E. Photograph of the copulatory bulb.