As with other members of Family Myidae, this species has a shelflike or spoonlike chondrophore projecting from the hinge plate of the left valve, has two adductor muscles of similar size, and no radial ribs. Mya arenaria has a well-developed, deep pallial sinus (photo). The chondrophore (on the left valve) is well-developed, projecting as far or nearly as far as it is wide (photo). The umbones are only slightly anterior to the middle (photo). The hinge ligament is internal, attached to the chondrophore (photo). The posterior end of the shell is less smoothly rounded than is the anterior but it is not truncate. The valves may gape slightly at each end, especially the posterior end (photo). The shell is brittle and chalky white or gray outside with some light yellow or brownish periostracum and uneven concentric rings. The siphons are light brown with darker tips (photo). Length to 17 cm, most often 10 cm or less in our area.