A new genus and four new species of Chamidae (Mollusca, Bivalvia) from the Indo-West Pacific with reference to transposed shells

Four new species of Chama, Eopseuma and Carditochama n. gen. (Bivalvia: Heterodonta) are described based on material from tropical Indo-West Pacific offshore waters. The dentition of the adult shells of Eopseuma species is corbiculoid-type and that of Carditochama species is lucinoid-type. Both genera exhibit a paedomorphic condition of the hinge, namely a radial arrangement of cardinals. I n. sp. has both "normal" and "inverse" forms. The dentition and size of the early dissoconch suggest that E. palaeodontica is foundamentally an "inverse" species. The similarity of the hinge arrangement of "normal" and "inverse" forms in infraspecies or infrageneric taxa is not a result of convergence of different phylogenetic groups that share similar habitats, but is a result of transposition of the shell and hinge. A full developmental study is necessary to discuss the intergeneric similarity. Although "inverse" forms of Chamidae usually show transposition of both the shells and hinge, the "inverse" form of Carditochama mindoroensis n. gen. and n. sp. exhibits transposed shells with "normal" dentition. Therefore, transposition of hinge and shell can occur independently.