Habitat: Present in shallow water, in gravelly mud. Distribution: This species has been reported from South Carolina to the West Indies. Natural History Notes: This species is often confused with another species, Atrina seminuda, because they cannot be distinguished using external characteristics. Their differences rely in the soft parts and the muscle scars. Depth: 2.5 m Characteristics: Atrina rigida can reach a length of up to 1 ft. The dorsal margin is straight and the ventral margin is more rounded. The valves have 15 rounded ribs and are covered with fine spines. The shell has a dark purple coloration.