Echinoplana celerrima Haswell, 1907

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 : 59-60

Echinoplana celerrima Haswell, 1907

Morphological features. Specimens are brownish. Tentacles are absent. Cerebral and tentacular eyes form two elongated paramedian bands ( Fig. 1A ). Ventral surface is whitish transparent and shows the ruffled pharynx, the two sperm ducts and the two uteri. A corrugated surface is present between male and female genital pores ( Fig. 2A ). It is formed by a whitish area provided with a number of ventral wall deformations or horizontal ventral folds. The largest folds are located in the middle of whitish area.

Reproductive features. The male copulatory apparatus is provided with cirrus armed with sclerotized spines. Prostatic vesicle is of interpolated type. Seminal vesicle is ventral. The female copulatory apparatus is formed by a narrow vagina formed by three section, external vagina or female atrium, median vagina or shell chamber where open several shell glands and internal vagina where are connected separately the two uteri. Ovaries are dispersed mainly in the ventral parenchyma between digestive ramifications. Histological sections of female gonads show a ventral germinative zone containing young oocytes and dorsal growing zone containing growing oocytes ( Fig. 3A ).

Reproductive behaviour. During animal culture, specimens were seen to cover their egg plates with their bodies. Even after being moved to other area of the same container, they returned again to cover their eggs.

Associated fauna. Specimens were found to be associated with proseriates (marine free-living flatworms) and sea urchin Paracentrotus lividus (Lamarck, 1816) .

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 2. Organs of attachment in Polyclads. A: ventral corrugated surface (cs) located between two genital pores of Echinoplana celerrima, scale bar: 0.2 mm. B: Genital pit (gp) in the acotylean Leptoplana mediterranea. This structure is located between the two genital pores. The two vasa deferentia (vd) unite in a common vas deferens (cvd) before entering the seminal vesicle (sv), scale bar: 0.2 mm. C. Ventral view of Prosthiostomum siphunculus showing a developed true sucker (ts) and a tubular pharynx (ph), scale bar: 1 mm.

Figure 3. Ovaries in polyclads A: Section through ovary of Echinoplana celerrima showing a ventral growing zone (grz) and a dorsal germinative zone (gmz), scale bar: 0.01 mm. B: Section through ovary of the cotylean Thysanozoon brocchii showing a ventral germinative zone (gmz) and a dorsal growing zone (grz), scale bar: 0.01 mm.