Trochidae, Skeneidae et Skenéopsidae (mollusca, prosobranchia) de la région de Roscoff. Observations au microscope électronique à balayage

Some scanning electron microscopy observations have been conducted on different species of Prosobranches from the Roscoff area: Trochidae, Calliostoma zizyphinum, Gibbula magus, Gibbula cineraria, Gibbula tumida, Cantharidus clelandi, Cantharidus exasperatus, Cantharidus montagui, Cantharidus striatus; Skeneidae, Skenea serpuloides, Skenea cutleriana, Skenea nitens; Skeneopsidae, Skeneopsis planorbis. Observed with closer attention are the protoconch and the first juvenile spiralial whorls. The studied Trochidae have a protoconch of about one spiralial whorl; the spire is round, with an oval opening and a fine ornamentation in G. magus and C. striatus, and in G. cineraria, G. tumida, C. clelandi, C. exasperatus and C. montagui, one can notice a dorsal umbilicus which is more or less marked and a beak at the opening. The morphology of the three studied Skenea species' protoconches is close to that of the Trochidae but also to that of the Rissoellidae. All these species develop without or with a very short pelagic phase.