Pleioplana okusi Bulnes, Kalkan & Karhan, 2009

Gammoudi, Mehrez, Bulnes, Verónica N. & Kurt, Güley, 2022, The polyclad fauna (Platyhelminthes, Rhabditophora) of the Sinop Peninsula (Black Sea, Turkey) with a description of a new species of Cryptocelis Lang, 1884 Abstract, Mediterranean Marine Science (Hong Kong, China) 22 (1), pp. 141-156 : 154

Pleioplana okusi Bulnes, Kalkan & Karhan, 2009

( Fig. 7B , 8 and 9E )

Material examined. One mature specimen, 22.10.2013, station M4, 4 m deep. One specimen, 02.07.2014, station M4, 4 m deep. Both specimens sagittally sectioned (20 and 19 slides).

Description. Body elongated oval 5 mm long, 2 mm wide. Tentacles wanting. Dorsal background color brownish, with a pattern of black spots less densely arranged towards the margin ( Fig. 8E ). Ventrally colorless. Tentacular eyes present. Cerebral eyes in two clusters, deeply embedded in the parenchyma ( Fig. 8E ).

Digestive system. Ruffled pharynx located in the second third of body. Mouth opening at mid-body, in the middle of the pharyngeal pocket.

Reproductive system. Male copulatory complex directed backward. The vasa deferentia pierce separately the elongated oval seminal vesicle. The latter oriented horizontally and located near the ventral body wall. Ejaculatory duct projecting into the interpolated oval-shaped prostatic vesicle. Its inner lining folds organized as tubular chambers ( Fig. 7A ) filling completely the lumen of the prostatic vesicle (Atomata-type, Faubel 1983). Ejaculatory duct distally armed with a sclerotized stylet, housed in a ciliated narrow male atrium ( Fig. 6C ) opening to the exterior by a small male genital pore.

Female gonopore immediately behind the male one. The narrow external vagina runs dorsally to form the median vagina lined by a deeply folded epithelium. After receiving separately the paired oviducts, continues distally and opens to a spherical Lang’s vesicle. Ovaries dorsal ( Fig. 7B ).

Masses of sperm were observed in the vagina, Lang’s vesicle, and protruding from the female atrium ( Figs. 6C , 7C and D ).

Remarks. The color pattern, eye arrangement, form, and position of the pharynx, as well as the microanatomy of the reproductive system, agree with the description of the specimen of Pleioplana okusi from the type locality in the Bosporus Strait ( Bulnes et al. 2009). The only difference we detected was the absence of any trace of tentacles in the specimen from the Black Sea, while the authors described the presence of tentacular knobs in the specimen from Altinkum (Bosporus Strait).

The presence of spermatozoa in the vagina and protruding from the female gonopore of a specimen of Pleioplana okusi suggests that direct copulation may be part of the mating behavior of this species. Galleni & Gremigni (1989) have already proposed that the presence of a Lang’s vesicle may be associated with true copulation during mating, and this observation in P. okusi may provide further evidence that supports this hypothesis.

Figures

Fig. 7: A, Prosthiostomum siphunculus; B, Pleioplana okusi. The arrow points the sperm mass. Abbreviations to the figures: cg, cement glands; dLv, Lang's vesicle duct; fp, female gonopore; i, intestine; Lv, Lang´s vesicle; mp, male gonopore; pv1, prostatic vesicle 1; pv2, prostatic vesicle 2; st, stylet; sv, seminal vesicle; u, uterus; v, vagina. Scale bars: A: 200 µm; B: 200 µm.

Fig. 8: Pleioplana okusi. A, sagittal section of the prostatic vesicle; B, sagittal section of the ovary; C-D, sagittal section of the vagina and female atrium. The arrows point the sperm mass. Abbreviations to the figures: ch, tubular chamber of the prostatic vesicle; ed, ejaculatory duct; fg, female gonopore; o, ovary; pi, epidermal pigment; pp, penis papilla; pv, prostatic vesicle. Scale bars: A: 100 µm; B: 50 µm; C: 30 µm; D: 50 µm.

Fig. 9: Diagrams of the external morphology of: A, Cryptocelis sinopae; B, Echinoplana celerrima; C, Leptoplana mediterranea; D, Leptoplana tremellaris; E, Pleioplana okusi; F, Prosthiostomum siphunculus. Scale bars:A-F, 3 mm.

Fig. 6: Sagittal sections of the reproductive system of A, Echinoplana celerrima; B, Leptoplana mediterranea; C, Leptoplana tremellaris. Abbreviations to the figures: cb, cirrus bulb; cg, cement glands; cr, cirrus; ed, ejaculatory duct; mp, male gonopore; ph, pharynx; pv, prostatic vesicle; sv, seminal vesicle; vd, vas deferens. Scale bars: A: 500 µm; B: 200 µm; C: 500 µm.