Discocelis tigrina (Blanchard, 1847) Lang, 1884

Gammoudi, Mehrez & Tekaya, Saïda, 2017, Suborders Acotylea and Cotylea (Polycladida): Study on morphological, ecological and reproductive features of some representative species from Tunisian coasts (Mediterranean), Ecologica Montenegrina 10, pp. 58-70 : 61-62

Discocelis tigrina (Blanchard, 1847) Lang, 1884

Morphological features. The body is oval shaped with a posterior end more pointed than the anterior. The length of specimens can reach 25 mm. Dorsal face is cream to white. Many small spots of brown color are present throughout the dorsal surface and are more concentrated on the median line. Tentacles are lacking. Tentacular and cerebral eyes form two black clusters ( Fig. 1C ). Marginal eyes are distributed along the two anterior thirds of body. Observation of whitish transparent ventral face shows a huge ruffled pharynx ( Fig. 4A ).

Reproductive features. A pair of uteri and a pair of vasa deferentia are visible by transparency in living specimens extending on either side of the pharynx ( Fig. 4A ). A common genital pore located in the second fourth of body. Pyriform prostatoid organs provided with muscular wall are seen also by transparency. The female genital apparatus is provided with a horse-shoes shaped Lang’s vesicle ( Fig. 4A ).

Histological sections show the common antrum, the prostatoid organs and the vagina ( Fig. 4B ). The diagrammatic reconstruction of copulatory apparatus show the male apparatus formed by the penis and prostatoid organs projected in a common antrum. The genital pore is common. The female apparatus is formed by vagina and Lang’s vesicle ( Fig. 4C )

Associated fauna. They were found essentially among oysters Crassostrea gigas (Thunberg, 1793) . It is likely that the flatworms are feeding on the bivalves.

Figures

Figure 1. Anterior dorsal region in A: Echinoplana celerrima. See the tentacular (te) and cerebral eyes (ce) forming two paramedian bands, scale bar: 0.5 mm. B: Letoplana mediterranea. See clusters of tentacular (te) and cerebral eyes (ce), scale bar: 0.5 mm. C: Discocelis tigrina. Note the presence of cerebral and tentacular eyes clusters, scale bar: 0.5 mm. D: Imogine mediterranea. Note the presence of two everted nuchal tentacles (arrows), scale bar: 0.5 mm. E: Yungia aurantiaca. See the two marginal tentacles (arrows) and cerebral eyes spots (arrowhead), scale bar: 1 mm. F: Thysanozoon brocchii. Dorsal faces provided with papillae and developed marginal tentacles (arrows), scale bar: 1 mm. G: Prostheceraeus moseleyi. Note the presence of marginal tentacles (arrows) and yellow marginal line, scale bar: mm. H: Prosthiostomum siphunculus. The cerebral eyes (ce) are not included in the semi circle formed by marginal eyes (me), scale bar: 1 mm.

Figure 4. Copulatory apparatus in Discocelis tigrina. A: ventral view showing by transparency the ruffled pharynx (ph), the two uteri (ut), the two vasa deferentia, the common gonopore (cg), the common atrium (ca), the prostatoid organs (po) and the Lang’s vesicle (Lv), scale bar: 0.5 mm. B: Section through common copulatory com; mon atrium (ca) showing prostatoid organs (po), vagina (v), uterus (ut) and vas deferens (vd) scale bar: 0.1 mm C: Diagrammatic reconstruction of copulatory apparatus. common gonopore (cg), common atrium (ca), ejaculatory duct (ed), Lang’s vesicle (Lv), Penis (p) and prostatoid organs (po), scale bar: 0.1 mm.