Bivalves are a class of marine and freshwater mollusks that have bodies enclosed by a hinged shell consisting of two parts. Fossilized bivalves are significant in paleontology and biostratigraphy, providing insights into ancient marine environments and helping to date sedimentary rock layers. Bivalves are also key indicators of water quality and environmental change.
Source Stanley, S. M. (1970). “Relation of Shell Form to Life Habits of the Bivalvia (Mollusca).” The Geological Society of America Memoir 125.