Limpets are common mollusks of the class Gastropoda and order Patellagastropoda. They are characterized by a shell that is generally low, flat, oval, bilaterally symmetrical and it covers the entire soft body, so that the living animal inside is rarely visible. Unlike a snail shell, limpet shells are not coiled. Limpets adhere strongly to rocks and other solid surfaces by means of a broad muscular foot. It is important for their survival that they are not dislodged easily, since their shell structure does not permit withdrawal into the shell.
The Atlantic plate limpet is Tectura testudinalis; testudinal means resembling a tortoise shell. The common European limpet is Patella vulgata. The patella in human anatomy is the kneecap so patelliform means like a kneecap.
Limpets are prosobranch snails, which allies them with the keyhole limpets, abalones, periwinkles, and cone shells. Five families of limpets are generally recognized. Lottiidae includes the genus Tectura and a number of Pacific coast species of the genus Lottia. Patellidae includes the genus Patella. The small white Acmaea mitra of the Pacific coast and a few deep-sea limpets make up the Acmaeidae family.
Limpets are intertidal herbivores, and they do not often feed when exposed to the open air. Most species have a radula, a rough ribbonlike structure with projections resembling teeth, that helps tear up the animal’s food and bring it to its mouth. The food then passes through a simple stomach, where it is exposed to enzymes from paired digestive glands, and then into a long, coiled intestine, where it is turned into feces. Most limpets are not stationary, but make forays of up to 5 ft (1.5 m) at night or at high tide, then return to their original position, which is sometimes marked by a “home scar” on the rock surface. The brain of limpets consists of a relatively small number of neurons, and it is not clear how they find their way home.
Male and female limpets look much the same, and can be distinguished only by the color of the gonads and microscopic examination of their sex cells, or gametes. In some species, protrandry has been observed. Males were identified and marked during one spawning season. The subsequent year, thirty percent of those marked were females. During reproduction, eggs and sperm are released into the water at the same time. After several days, 10 for Patella, the larvae settle on some solid substratum and grow into adults. The larvae of Lottia strigatella settle on boulders where adults of the same species are established, even though other species may be present. This is known as gregarious settlement.
The largest limpet is Lottia gigantea, a Mexican species 4-8 in (10-20 cm) long. Most species of limpets are 0.4-1 in (1-2.5 cm) long. Some species have been estimated to live 15 years. The larger species are consumed, cooked or raw, in various parts of the world, but limpets are not known to support a commercial fishery.
The key-hole limpets are not true limpets but are members of the order Archaeogastropoda and family Fissurellidae. Key hole limpets have an opening near the apex of the shell, giving the appearance of a miniature volcano and permitting the outflow of fecal matter and water that has already passed over the gills. The hole begins as a slit in the embryonic shell, and becomes closed as the mantle deposits more shell during growth to adult size. A common species of keyhole limpet is Diodora cayenensis, which ranges from New Jersey to Brazil.
Brusca, Richard C., Gary J. Brusca, and Nancy J. Haver. Invertebrates. Sunderland, MA: Sinauer Associates, Inc., 2003.
C. S. Hammen