The shells are subcircular and irregular in outline, robust, and inequivalve. Most Chamidae species live cemented to hard substrates, but can be attached by either the left or right valve. In either case, the “lower” valve has a large attachment scar and is more inflated and larger than the flatter “upper” valve.

The shell is composed of aragonite, and the exterior is rough and irregular, and covered in numerous, commarginal and/or radial, scaly spines in many species. Valve interiors have a simple, uninterrupted pallial line. Between the pallial line and the edge of the shell margin is a flat commissural shelf that, depending on the species, can be smooth or denticulate.

Source: Mikkelsen, P.M., and Bieler, R. 2008. Seashells of Southern Florida: Bivalves. Princeton, New Jersey: Princeton University Press. 503 pp.