The name Limpet is used for many marine and freshwater gastropod species which have a simple conical shell. The phrase "true limpets" is used only for marine limpets in the ancient clade Patellogastropoda. This article is mainly about the true limpets.
True limpets are small marine gastropod molluscs with flattened, cone-shaped shells. They live throughout the intertidal zone, attached to rocks or other hard ground. They attach themselves using mucus and a muscular "foot", which seals them against the rock and protects them from desiccation during low tide, and from high-energy waves action.
Limpets eat by grazing on algae found on rock surfaces. They scrape films of algae from the rock with a radula, a ribbon-like tongue with rows of teeth. Limpets move by rippling the muscles of their foot in a wave-like motion. Most limpets are less than 3in (8cm) long, but a West Mexican Limpet grows to be 8in (20 cm).
Some key-hole limpets have a hole at the top, through which gas exchange can occur (they are not true limpets).
There are many limpets in the Paleozoic fossil record, from the lower Cambrian, but none can be placed with certainty in the Patellogastropoda. Some might be Monoplacophorans, which is a separate mollusc class with a similar life-style. The earliest patellogastropod verified by shell microstructure is from the Triassic of Italy, but it is in the Upper Cretaceous and Cainozoic periods that many of the living forms make their first appearance.
The life-style of limpets is sessile: they stick fast to rocks or other hard substrates.
Some species of limpets return to the same spot on the rock known as a "home scar" just before the tide ebbs. It is thought that they follow chemical trails. In such species, the shape of their shell often grows to precisely match the contours of the rock surrounding the scar. This behaviour permits a better seal to the rock. It is thought that they follow a mucus trail left as they move.
Where the limpets eat the algae, off bare rocks, it causes places where other organisms can grow and thrive. Some species, such as "Lottia gigantea" "garden" a patch of algae around their home scar. They push other organisms out of this patch by ramming with their shell, allowing their patch of algae to grow for their own grazing.
Limpets are prey for starfish, shore-birds, fish, seals, and humans. They have a two main defences; fleeing (letting go in the water) or clamping their shells against the surface they are on. The defence response can be adjusted to the type of predator, which can often be detected chemically by the limpet.
Limpets can be long lived, with tagged specimens surviving for more than 10 years. If the limpet lives on bare rock, it grows at a slower rate but can live for up to 20 years.
Limpets found on sheltered shores (limpets that are less frequently in contact with wave action, and thus less frequently in contact with water) have a greater risk of desiccation because of the effects of sunlight, water evaporation and the wind. To avoid drying out they will clamp to the rock they inhabit, minimizing water-loss from the rim around their base. As this occurs chemicals are released that promote the vertical growth of the shell.
Limpets are hermaphrodites (producing both male and female reproductive cells) and undergo sex change during life. They become male at about 9 months, but after a couple of years they change sex to become female. Spawning occurs once a year, usually during winter, and is triggered by rough seas which disperse the eggs and sperm. Larvae are pelagic for a couple of weeks before settling onto a hard substrate.
Abalone
Abalone (from Spanish "Abulón") are shellfish, a genus of gastropods.
Abalone are known by their colorful "pearlescent" inside shell. This is also called ear-shell, "ormer" in Guernsey, "abalone" in South Africa, and "pāua" in New Zealand.
The meat of this shellfish is thought to be delicious in some parts of Latin America (especially Chile), South East Asia, and East Asia (especially in China, Japan, and Korea).
Abalones live all over the world, They can be seen along the waters of every continent, except the Atlantic coast of South America, the Caribbean, and the East Coast of the United States. Most abalones are found in cold waters, along the coasts of New Zealand, South Africa and Australia, and Western North America and Japan in the Northern Hemisphere. In the Chilean Pacific coast, the species called loco ("Concholepas concholepas") has a hard, black shell, and is eaten by many people.
Abalone have unique features: the shell is round, with two to three spirals. The last spiral is grown into a large "ear"-like shape, which explains the name 'ear-shell'. The inside of the shell is shiny, from silvery white to green-red mother-of-pearl.
Abalones can start to give birth at a small size. Their fertility is high and increases with size (from 10,000 to 11 million eggs at a time).
Young albalones, called larvae, feed on plankton. The adults eat plants and feed on algae. They like to eat red algae. Their size can be as small as 20 mm to as big as 200 mm.
The shell of the abalone is known for being very strong. It is made of very tiny calcium carbonate tiles stacked like bricks. Between the layers of tiles is a sticky protein substance. Allergic skin reactions and asthma attacks can happen when breathing the dust made when these tiles are broken down.
The colorful inside part of the abalone shell can be used for decorative inlays, in guitars, for example.
Sport harvesting of red abalone is allowed with a California fishing license and an abalone stamp card. Abalone may only be taken using breath-hold techniques: freediving or shorepicking. SCUBA diving for abalone is strictly not allowed. Abalone harvesting is not allowed south of the mouth of the San Francisco Bay. There is a size minimum of seven inches measured across the shell and a limit of three per day and 24 per year that can be taken. Abalone may only be taken in April, May, June, August, September, October and November, but they may not be taken in July, December, January, February or March. Transportation of abalone is only legal while the abalone is still attached to the shell. Sale of sport-caught abalone is illegal, including the shell. Only red abalone may be taken; black, white, pink, and flat abalone are protected by law.
Abalone divers normally use a very thick wetsuit, including a hood, booties, and gloves. They also wear a mask, snorkel, weight belt, abalone iron, and abalone gauge. It is common to take abalone in water a few inches up to 10 m/28' deep. Fewer freedivers can work deeper than that. Abalone are normally found on rocks near food sources (kelp). An abalone iron is used to pry the abalone from the rock before it can fully clamp down. Visibility is normally five to ten feet. Divers commonly dive out of boats, kayaks, tube floats or directly off the shore. An eight-inch abalone is considered a good catch, a nine-inch would be very good, and a ten-inch plus (250 mm) abalone would be an excellent catch. Rock- or shore-picking is a different method from diving where the rock picker feels below rocks during low tides for abalone.
There has been a trade in diving to catch abalones off parts of the United States coast from before 1939. In World War II, many of these abalone divers were recruited into the United States armed forces and trained as frogmen.