Clams are called bivalves because they have two shells (valves). The valves are lined with a thin membrane, which is termed the mantle. The mantle encloses the visceral_mass and the muscular_foot.
Opening and closing of the valves is regulated by the anterior and posterior_adductor_muscles. Gills are used for respiration as well as filter-feeding. The muscular foot assists with movement. The anterior_adductor_muscle is positioned between the mantle and the foot and helps the clam burrow in sand.