[Populations or species? Research on the significance of the transmission of Trematoda Lepocreadiinae (T. Odhner, 1905) in 2 marine ecosystems].

Two ophthalmotrichocercous cercariae, very similar as concerns their morphological and anatomical characteristic, parasitize two distinct species of marine Prosobranches: Sphaeronassa mutabilis and Amyclina corniculum. The development of these two cercariae has been followed through the corresponding adult stages. The life cycles of these two lines of Trematodes were shown to be different not only for the first intermediate host but also for the second hosts (Pelecypods); only the final hosts are shared (Sparus auratus, Pagellus erythrinus and P. mormyrus). Additionally the endemiotops (where the life cycle develops) are fundamentally different. Beaches of fine sand with a depth of 0 to 10 m are the endemiotop of the line arising from S. mutabilis whereas hydrodynamically calm muddy biotops (depth between 0 and 10 cm) found at the periphery of prairies of Cymodocea nodosa are the endemiotop of the line arising from A. corniculum. A biometrical study of every larval stage shows significant differences between those two lines. In spite of these differences, the most part of morphological, anatomical and biological characteristics are the same among the various stages of the two lines. So we think the two lines could be, in fact, two populations of the same species, Lepocreadium pegorchis M. Stossich, 1900 which are found together into the definitive hosts, because these fishes are living into the ecosystems characteristic of the two lines. If so, we should be faced to a noteworthly example of ecological vicariance.