They are separate from each other and short, so the hard clam does not burrow deeply. Its white interior has a deep purple stain surrounding its muscle scar, and its hinge has three white cardinal teeth. This species may grow to a width of four inches. The life cycle of the hard clam includes a pelagic larval phase and relatively sedentary benthic juvenile and adult phases. Hard clams begin their adult lives as males, often become females with greater maturity, and require individuals of both sexes for reproduction.
Clams develop functional male gonads during the first or second year of life.
Spawning cycles are affected mainly by water temperature and the availability of food, and thus vary according to latitude. Female fecundity is high, and individuals can release 16 million to 24 million eggs per spawn, although laboratory studies often have recorded values of only 1-3 million eggs, and only a few will reach maturity. Individuals may release as many as 60 million eggs during one season. Eggs are 70 to 73 microns in diameter and are surrounded by a gelatinous membrane. Eggs and sperm of adults are expelled in the water current and fertilization occurs externally in the water column.