Several gastropods shells from the Roscoff area were observed with the scanning electron microscope : Pyramidellidae : Odostomia acuta, O. unidentata, O. turrita, O. plicata, O. scalris, O. lukisi, Turbonilla crenata, T. elegantissima, T. innovata, Chrysallida decussata, C. excavata, C. obtuse, C. spiralis, Evalea oblique; Philinidiae: Philine catena; Retusidae: Retusa mammillata, R. truncatula. The Protoconch and the lst juvenile turns are particularly studied. In the Pyramidellidae, there are 4 types of protoconchs: (1) type A: senestral protoconch, turriculated, axis perpendicular to the teloconch, present in Odostomia acuta, O. unidentata, O. turrita, O. plicata and Turbonilla elegantissima, species with pelagic development (like O. acuta, described by Thorson). (2) type B: senestral protoconch, globular and planorbiform, present in Turbonilla crenata, spp with pelagic development. (3) type C: senestral protoconch; apex with a small granular ornementation masked under the last whorl, present in Evalea oblique, spp with a direct development or a very short pelagic one. (4) type D: senestral and smooth protoconch, apex masked under the last whorl, present in Odostomia scalaris, Turbonilla innovata, Chrysallida decussata, C. excavata, C. obtuse, C. spiralis, spp with direct development or short pelagic development (like Odostomia eulimoides, described by Lebour). In the Retusidae, the Retusa truncatula protoconch is situated in the cavity of the teloconch whorls; the Retusa mammillata protoconch has a very proeminent position at the apex shell. |