On the Development of Bivalves belonging to the Genus Corbicula

Abstract

Small bivalves of the genus Corbicula are widely used for human food in Japan with some medcal meaning, thus, they have some commercial importance, and in some cases they are the object of cultivation being transplanted to the place where they are not found. Their habitat is either fresh or brackish water. The chief purpose of the present study is to elucidate their reproduction which shows different types according to ecological conditions. 12 species occurring from the North, Hokkaido, to the South, Formosa, may be grouped in view of their habitats and sexuality into 3 categories, as follows :
Group I. Fresh water-Monoecious-incubatory.
Group II. Fresh water-Dioecious-probably non-incubatory.
Group III. Brackish water-Dioecious-probably non-incubatory.
Here mainly the description of the first group represented by C. leana PRIME is given. In the species, which is incubatory in its habit, inner gill-lamellae are differentiated structurally for marsupial purpose. Its early larva is furnished with a velum which, being useless for swim-ming, is much better in its development compared with that of such species as Sphaerium. Post-larva with D-shape shell when compared to the same stage of marine bivalves shows more advanced condition in its general organization, that is, the said larva of the present species is already furnished with well developed functional gills, foot and byssus thread. The larva has no stage of parastic life.
With regards to the other groups, although their study is not completed yet, it may be conjectured from anatomical and histological observations so far carried out at many times in the year that they are non-incubatory. Further details will be published in the future.