Phylum Mollusca, Class Bivalve
Bivalves are two valves (shells) that are identical. This makes them different from brachiopods, which also have 2 connecting shells, but they are not mirror images of each other. These filter feeders are generally burrowing organisms, although attached, swimming and cemented bivalves evolve in the Late Paleozoic and Carboniferous.
Marine sessile benthic organisms (epifauna and infauna).