The morphology and behaviour of Cercaria lata Lespés, 1857 (Digenea, Faustulidae) from the Mediterranean clam Tapes decussata (L.).

Cercaria lata (Digenea, Faustulidae), discovered by Lespés (1857) in Tapes decussata (L.) in the basin of Arcachon, was found for the first time, from the eastern Mediterranean, in the same lamellibranch from Tunisia (Bizerte and Tunis lagoons and Gulf of Gabes). These cercariae develop in daughter sporocysts, which develop in mother sporocysts in the gonads. Daughter sporocysts are observed in the gonads and sometimes in the digestive gland. A redescription and the behaviour of the naturally emerging cercariae and spatio-temporal distribution of the sporocysts are reported. A comparative study using multivariate analyses associated with morphology, biology and seasonality confirm the distinctness of Cercaria lata and the cercaria of Cercaria pectinata from Donax trunculus.

[Estimation of fertility and quality of oocytes emitted by the clam Ruditapes decussatus (Linnaeus 1758) during experimental inductions]. / Estimation de la fécondité et de la qualité des ovocytes émis par la palourde Ruditapes decussatus (Linné 1758) lors d'inductions expérimentales.

Experimental inductions were carried out on some genitors of clams Ruditapes decussatus to obtain sexual emissions and estimate the fecondity of this species. The genitors were collected from two sites of tunisian littoral. Higher percent of oocytes was found in summer with a maximum of 52 x 10(4) oocytes in Gargour (Golf of Gabès) against 45 x 10(4) in Menzel-Jemil (Lagoon of Bizerte). The observation under the electronic microscope of free oocytes allowed us to subdivised them in three groupes: immatures, matures and atretics. Only mature oocytes were susceptible to be feconded and underwent larval development with unknown proportion.