Echinoplana celerrima Haswell, 1907

General features. The body is elongated oval shaped. Tentacles are wanting. The color of dorsal surface is brownish (Fig. 2a). The length can reach 40 mm. Tentacular and cerebral eyes form two anterior symmetric clusters. The formers are larger and more posterior than cerebral eyes (Fig. 2b). Ventral surface is white and transparent. The ruffled pharynx is visible and shows 12 to 16 lateral folds.

Reproductive apparatus. Testes are mainly ventral and dispersed between digestive ramifications. They form a small follicles enwrapped each one by e basal membrane. Each testis contains different stages of germs cells (Fig. 2f). Ovaries are less numerous and located mainly in dorsal parenchyma. The seminal vesicle occurs just behind pharyngeal cavity. The main feature of copulatory apparatus is the presence of brown line located in the last third of body which correspond to the cuticularized cirrus. A comb-shaped corrugated surface is present between the two genital pores (Fig. 2c). Two vas deferens lie in both sides of pharynx enter the oval shaped seminal vesicle located behind the pharyngeal cavity. The seminal vesicle is close to ventral wall and communicates with a tubular prostatic vesicle of interpolated type. This vesicle have internal lining provided with radial folds and characterized by a very thick muscular wall consisting of an external layer of longitudinal fibres and a well-developed internal layer of circular fibers. The prostatic vesicle is connected to the eversible cirrus armed with sclerotized spines (Fig. 2d, e).

The vagina is formed by three sections, the vagina externa, the vagina media, and the vagina interna. The former is narrow. The second is known as shell chamber and receive secretions of shell glands. The vagina interna receive the uteri filled with eggs (Fig. 2g).

Habitat. Four specimens of Echinoplana celerrima were collected from a depth of 20 m. All specimens were found to be associated with the very abundant tunicate Ciona intestinalis . Other associated animals are presented by the sea urchin Paracentrotus lividus (Lamarck, 1816) and the starfish Asterina gibbosa (Pennant, 1777) .