The heavy ridges that stand out from the shell represent slow winter growth. Commensal crabs often are found living inside the shells of butter clams. Note that some shells have a hole near the hinge. These two carnivorous snails use a file-like object called a radula to drill the hole, releasing the suction holding the butter clam shells together, then push their way into the butter clam and eat it. The Japanese oyster drill, a small snail about an inch long, was imported accidentally from Japan along with Japanese oysters earlier in this century.
Humans are also an important predator in the intertidal zone.