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Knowing Nature . . .

Life of a Limpet

November 27, 2007
Jocie Ingram

Fun Facts

  • British artist J.M.W. Turner’s painting “War, the Exile and the Rock Limpet” from 1842 depicts a solitary Napoleon on exile on the island of St Helena, standing before a limpet.
  • Limpets have been harvested by humans for 150, 000 years. Traditionally, Hawaiian limpets, known as “opihi” are considered a delicacy.
  • Some South African species of limpets are territorial and aggressive, and use their shells as battering rams.
  • Due to the limpet’s clinging ability, some mines built for attaching to ships in World War II were called "limpet mines".

Limpets cling to rocks, like dozens of little pointy hats. They don’t capture our attention the way moving creatures such as crabs and fishes do. Nor do they dazzle us with bright colours, like orange and purple sea stars. Despite this neglect, limpets are interesting creatures that are an important part of marine ecology.

Limpets belong to a large group of creatures called Mollusks. Classified within mollusks are gastropods, which include snails, slugs, abalone and limpets.

Gastropods are soft-bodied animals, with internal organs that are protected by a flap of tissue called a mantle. Many gastropods have shells, though some, like slugs, have evolved to have no protective shell. Gastropods also have a muscular foot used for locomotion.

Limpets are univalves, which means that they have one shell. This shell is oval and cone shaped, with a pointed apex that may be in the center, or off-center. The shell has concentric growth lines, and is often attractively decorated with tortoise-shell grey, brown and white patterning. The inside is a polished bluish-white, with a dark brown center. The largest limpets are about 10 cm long, though most are considerably smaller.

photo © Dave Ingram

The most visible organ on the underside is a large, muscular foot, which propels the limpet forward with a rippling motion. The foot also enables the limpet to suction onto rocks. The mantle, which lines the inside of the shell, encases the internal organs, called the “visceral mass”. True limpets have a single gill, though some types of limpets have two gills.

Like their relatives the snails, limpets have a head and a pair of antenna-like tentacles. When limpets move, the head emerges slightly from the shell and the tentacles may be visible. On the underside of the head is a mouth, with a rasping tongue called a radula.

Feeding at night, limpets graze on algae that they scrape off with their tongues. Interestingly, many species of limpets have a strong homing instinct, and after feeding return to their “home” spot. How and why they return to the same spot is a mystery.

Most limpets have separate male and female individuals, and reproduce by releasing egg and sperm directly into the water. They begin life as free-swimming larvae, before settling on the surface of a rock or seaweed.

photo © Dave Ingram

Some limpets are adapted to living high up on the beach, where they are subjected to freezing temperatures, fresh water from rain, and searing summer heat. Limpets often adhere to a crack in a rock, where there is moisture. When exposed, their shell protects them from drying out, and from predators such as shorebirds, small mammals, sea stars and crabs.

Many species of limpets are found along the coast of the Pacific Northwest. Highest on the beach are the distinctive finger limpets (Lottia digitalis), which have white finger-like ribs on a brown backdrop. Another common limpet is the mask limpet (Tectura persona), which is about 3-4 cm long with a speckled brown and white pattern, and an apex that is off centre. A somewhat similar species is the plate limpet (Tectura scutum), which has a flatter profile, and a centered apex.
Other species may be found only at low tide, such as the rough keyhole limpet (Diodora aspera). This limpet has a hole in the apex, like the crater of a volcano. The whitecap limpet (Acmaea mitra) has a thick white shell, and a high cone-shaped profile. It is often crusted over with pink coralline algae. The whitecap limpet, also called “dunce cap limpet” is often found washed up on the beach.

Though many limpets are found attached to rocks, some species attach to other surfaces. Some are specialized to attach to marine plants, such as the eelgrass limpet. Another species, the black limpet, lives attached to black turban snails.

Limpets are best observed in situ, and should not be pried off rocks. Doing so will damage the limpets’ ability to suction, resulting in the death of the limpet. Limpets are certainly not as stationary and lifeless as they appear. These interesting animals, with their delicately patterned shells, are well worth a second look.

Click on a link below to view the CVNS newspaper column.

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