Limpet

a small, conical shellfish. The shell is much like that of one-half of a clamshell surrounded by a leathery fringe or border. The limpet fills the shell and clings by its exposed side to a rock. By raising the middle of its body slightly it creates "suction" and is held so firmly to the rock by atmospheric pressure that it is not easy to pick it off. At low tide British fishermen gather limpets for bait, and millions are collected on the Irish coast for food. Limpets go about when the tide is in, feeding on seaweeds which they rasp away with a rough file-like tongue. It is said a limpet "homes," or returns to the same spot on a rock, till it oftentimes wears a depression.