Echinoplana celerrima Haswell, 1907

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 : 151

Echinoplana celerrima Haswell, 1907

( Fig. 6A and 8B )

Material examined. Nine mature specimens, 21.01.2014, station M2, 4 m deep. Three mature specimens, 22.01.2014, station M3, 5 m deep. One specimen, 12.05.2014, 5 m deep, station M1. One specimen sagittally sectioned (16 slides).

Description. Body broadly oval. Preserved specimens between 8–25 mm long and 3–7 width. Dorsal surface background color brownish, ventrally colorless, and transparent. Tentacles wanting. Two elongated clusters of cerebral eyes, tentacular eyes basal, apparent only in a few specimens ( Fig. 8B ).

Digestive system. A ruffled pharynx lies in the midthird of the body and possesses 8 to 12 pairs of lateral folds. Mouth opening slightly posterior to the middle of pharyngeal pocket.

Reproductive system. Male gonopore behind the distal margin of the pharynx. Cirrus sac consisting of thick layers of musculature armed with sclerotized teeth. Prostatic vesicle interpolated, lined with glandular epithelium thrown into radial folds. Seminal vesicle four times smaller than prostatic vesicle and located ventrally to the latter ( Fig. 6A ).

Female gonopore 2.4 mm behind the male one. Between them, there is a corrugated surface consisting of glandular epithelium. The vagina is oriented anteriorly, Lang’s vesicle and ductus vaginalis not developed.

Remarks. The color pattern, the organization of the male system, and the presence of a corrugated ventral area between the gonopores (genital sucker) agree with the descriptions of Echinoplana celerrima from the Indo Pacific and Mediterranean waters ( Haswell, 1907; Galleni, 1979; Prudhoe, 1982; Holleman, 2007; Gammoudi et al. 2009); nevertheless, some variability was detected. The specimens from the Black Sea lack the median dark band and, in some of the revised material, the tentacular eyes were wanting although present in all other described specimens. Regarding the reproductive system, the Lang´s vesicle varies from rudimentary ( Prudhoe, 1982) to well developed, and with a ductus vaginalis ( Gammoudi et al. 2009). The rudimentary Lang´s vesicle in our sectioned specimen could suggest it was not fully mature.

Figures

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.

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.