limpet, any of various snails (class Gastropoda, phylum Mollusca) having a flattened shell. Most marine species cling to rocks near shore. A common American species is the Atlantic plate limpet (Acmaea testudinalis) of cold waters; the common species of Britain and northern Europe is Patella vulgata. Keyhole limpets, of the prosobranch family Fissurellidae, have a slit or hole at the apex of the shell, through which water currents (and wastes) exit.
Limpets belonging to the subclass Pulmonata live in brackish and fresh water. For slipper limpet, see slipper shell.