The Soft-Shell Clam Mya arenaria: Biology, Fisheries, and Mariculture

Chapter 2: Anatomy and Functional Morphology of the Soft-Shell Clam Mya arenaria

Victor S. Kennedy


Shell 25–150 mm (1–6 in) in length, elongately to roundly ovate, valves slightly gaping at the acute to rounded posterior. Color chalky-white with traces of cream … on inner surface. Umbones subcentral to central. Sculpture consists of concentric growth lines and obscure radiating surface irregularities. Ligament poorly developed. Chondrophore of the left valve long, spoon-shaped and shallow. Its anterior edge projecting sharply from the hinge line at an angle of 90–100° has an elevated recurved ridge particularly well-developed at the extremity… Distal margin broadly rounded. Projecting end of posterior tooth prominent, its proximal portion often badly worn. Margin sulcate on either side of tooth. The adjacent narrow ledge is flat and the pit slopes gradually anteriorly. Chondrophore right valve shallow, unevenly excavated, its lower portion flattened where ventral margin fuses with shell. Surmounting tooth never well-developed. Subcircular posterior adductor muscle scar situated in upper third of shell. Swollen base of lanceolate anterior scar lies about on the midline. Pallial sinus long and narrow, its length usually about twice its width. Upper and lower margins slope at the same angle. Periostracum thin, light gray to straw-yellow. [From Foster 1946]

In this chapter, I describe the anatomy and functional morphology of the soft-shell clam Mya arenaria (Figure 1) in broad strokes, referring the reader to relevant publications that provide greater detail on bivalve organs and organ systems and their functions. Such publications include textbooks on invertebrate biology like Ruppert et al. (2004) and books focused on mollusks, such as Gosling (2015) and the well-illustrated review by Ponder et al. (2020). Aspects of bivalve shell structure and morphology and of soft internal anatomy are described and illustrated by Allmon and Mikkelsen (2020) in the Digital Encyclopedia of Animal Life (Hendricks et al. 2015).