The identity of Isocrassina, Laevastarte and Ashtarotha (Mollusca, Bivalvia, Astartidae) and their representatives from beaches and estuaries in The Netherlands and Pliocene strata in Belgium

The identity of the subgenera Isocrassina Chavan, 1950, Laevastarte Hinsch, 1952, and Ashtarotha Dall, 1903, of the genus Astarte Sowerby, 1816 in the family Astartidae (Mollusca, Bivalvia) is discussed. Isocrassina has been widely used for Pliocene species in the North Sea Basin. Here it is demonstrated, that this is based on a redefinition of this subgenus, which excludes its type-species. As the North Sea species differ considerably from the type-species of Isocrassina in aspects of ornament and details of the hinge, it is concluded that they should be placed in the genus Laevastarte. A slightly modified definition of Isocrassina and Laevastarte is given and both are raised to genus level. The morphological basis for Ashtarotha is quite weak and it is found doubtful if it should be maintained. The species now incorporated in Laevastarte, known from the beaches and estuaries in the province of Zeeland (The Netherlands) are described and extensively illustrated. The present study also includes in situ specimens from excavations in the Antwerp region (Belgium) as well as from some boreholes in Zeeland. One new species, Laevastarte ovatacostata n. sp., and a new forma, Laevastarte bipartita (Sowerby, 1826) forma confusa are introduced. Neotypes are designated for Astarte omalii De la Jonkaire, 1823 and Astarte basterotii De la Jonkaire, 1823.