near the hinge line) and scallop shells lack a pallial sinus. Behaviorally, cockles live buried in sediment, whereas scallops either are free-living and will swim into the water column to avoid a predator, or in some cases live attached by a byssus to a substrate.

The mantle has three apertures (inhalant, exhalant, and pedal) for siphoning water and for the foot to protrude.