Any of various marine snails belonging to several families and genera, found in the Atlantic and Pacific oceans. A limpet has a conical shell and adheres firmly to rocks by its disclike foot. Limpets leave their fixed positions only to graze on seaweeds, always returning to the same spot. The common limpet (P. vulgata) can be seen on rocks at low tide (especially genera Acmaea and Patella).