Glycymeris

Glycymeris, common name the bittersweet clams, is a genus of saltwater clams, marine bivalve molluscs in the family Glycymerididae. The genus name comes from the Ancient Greek word glykymaris (perhaps from Glykys (sweet) and Meris (part)), a word which is only recorded once in Greek literature. These clams are very common in the fossil state, from Cretaceous period in the Valanginian age (between 140.2 ± 3.0 mya and 136.4 ± 2.0 mya). Fossil shells of these molluscs can be found all over the world. Genus Glycymeris includes about 100 extinct species. The shells are generally biconvex, with equal valves round in outline, and slightly longer than wide. Their size varies from medium to large. The external ligament lacks transverse striations. These clams are a facultatively mobile infaunal suspension feeders.