Limpet, a name applied to the gasteropod mollusks of the families patellidoe, calyptrceidce, and fissurellidce. The shell is conical, with the apex turned forward, variously ridged, and with more or less indented borders; the species are all marine, very numerous both living and fossil, and largest in the tropical seas. The common or rock limpet (patella) is more or less circular, conical above, flat below, furnished with a large, thick foot, by which it adheres very firmly to rocks and other shells; the food consists of seaweeds, which it rasps with the powerful tongue. In the second family, or bon-net limpet, belongs the "boat shell" or "ladies' slipper" (crepidula) of the New England coast, having a wide horizontal partition over half the shell, like the seat of a boat; they adhere very firmly to the rocks. In the third family, the keyhole limpet (fissurella) has the apex pierced by a small longitudinal fissure, resembling a keyhole.
1 Boat Shell (Crepidula). 2. Rock Limpet (Patella). 3. Keyhole Limpet (Fissurella).