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'Limpets' or "True limpets" are marine gastropod mollusks in the order 'Patellogastropoda'. Limpets have flattened, cone-shaped shells, but a limpet is a kind of snail, despite the fact that in adults the shell is not spirally coiled. They are commonly found attached to rocks, looking like little disks or bumps on the rock surface. In life, limpet shells are often covered in microscopic growths of green marine algae which can make them harder to see, as they ressemble the rock surface itself.
Various different species of limpet live throughout the intertidal zone, from the high zone (upper littoral zone) to the shallow subtidal, and representatives from the order live on the rocky coasts of all oceans world-wide.
They attach themselves to the substrate using pedal mucus and a muscular "foot". They can locomote using the foot when conditions are suitable, or they can "clamp down" against the rock surface with very considerable force when necessary, and this ability enables them to remain safely attached despite the dangerous wave action on exposed rocky shores. The ability to clamp down also seals the shell edge against the rock surface, protecting them from desiccation during low tide, despite their being in full sunlight.
When true limpets are fully clamped down, it is impossible to remove them from the rock using brute force alone, and the limpet will allow itself to be destroyed rather than stop clinging to its rock. This survival strategy has led to the limpet being used as a metaphor for obstinacy or stubbornness.
Most limpets feed by grazing on algae which grows on the rock (or other surfaces) where they live. They scrape up films of algae 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.
In some parts of the world, certain smaller species of limpet are specialized to live on seagrasses and graze on the microscopic algae which grow there. Other species live on, and graze directly on, the stipes (stalks) of brown algae (kelp).
The majority of limpet species have shells that are less than 3 in (8 cm) in maximum length. However, until quite recently a west Mexican limpet species was known to grow as large as 8 in (20 cm). This species may, however, now be extinct, as it was slow to reach maturity, and suffered from overcollecting, both as a food item, and by shell collectors and dealers.
In Hawaii, limpets are commonly known as ''opihi'', and are considered a delicacy. In fact, larger limpet species are, or were historically, cooked and eaten in many different parts of the world.
It is also worth noting that the word "Limpet" is an inexact term, which in everyday parlance can be applied to almost any gastropod with a simple conical shell, including gastropods in different families and even different orders. Thus patellogastropod limpets are often referred to as "True Limpets" to differentiate them from "Keyhole Limpets", "Slipper limpets", various pulmonate limpets, and so on.

Contents

Homing behaviour

Predators and threats

Taxonomy

References

Homing behaviour

Some species of limpets return to the same spot on the rock known as a "home scar" just before the tide recedes. In such species, the shape of their shell often grows to precisely match the contours of the rock surrounding the scar. This behaviour presumably allows them to form a better seal to the rock and may help protect from either predation or desiccation. It is still unclear how limpets find their way back to the same spot each time, but it is thought that they follow a mucus trail left as they move, this trail contains pheromones. Other species, notably ''Lottia gigantea'' seem to "garden" a patch of algae around their home scar ^[1]. They are one of the few invertebrates to exhibit territoriality and will aggressively push other organisms out of this patch by ramming with their shell, thereby allowing their patch of algae to grow for their own grazing. Also, where the limpets eat the algae off bare rocks, it creates places where other organisms can grow and thrive.

Predators and threats

Limpets are preyed upon by a variety of organisms including starfish, shore-birds, fish, seals, and humans. Limpets exhibit a variety of defenses, such as fleeing or clamping their shells against the substratum. The defense response can be determined by 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 exposed shores, which have fewer rock pools than sheltered shores and are thus in less frequent contact with water, have a greater risk of desiccation due to the effects of increased sunlight, water evaporation and the increased wind speed. 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 limpet's shell.
Limpets are being researched to see if the chemicals they release have cancer-preventing qualities.

Taxonomy

★ Suborder Lepetopsina

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★ Superfamily Lepetopsoidea

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★ Family † Damilinidae

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★ Family Lepetopsidae

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★ Family Neolepetopsidae

★ Suborder Nacellina

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★ Superfamily Acmaeoidea

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★ Family Acmaeidae

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★ Genus ''Acmaea''

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★ Genus ''Notoacmea''

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★ Genus ''Pectinodonta''

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★ Genus ''Problacmaea''

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★ Family Lepetidae

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★ Genus ''Bathylepeta'' Moskalay, 1977

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★ Genus ''Cryptobranchia'' Middendorff, 1851

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★ Genus ''Iothia'' Forbes, 1849

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★ Genus ''Lepeta'' J. E. Gray, 1842

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★ Genus ''Limalepta'' Moskalev, 1978

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★ Genus ''Propilidium'' Forbes and Hanley, 1849

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★ Genus ''Sagamilepeta'' Okutani, 1987

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★ Family Lottiidae

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★ Genus ''Lottia'' Gray, 1833

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★ ''Lottia gigantea'' Sowerby, 1834

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★ †''Lottia alveus'', Eelgrass limpet

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★ Superfamily Nacelloidea

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★ Family Nacellidae

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★ Genus ''Macklintockia''

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★ Genus ''Naccula''

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★ Genus ''Nacella''

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★ ''Nacella kerguelenensis'' (E. A. Smith, 1877

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★ ''Nacella macquariensis'' Finlay, 1927

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★ ''Nacella terroris'' (Filhol, 1880)

★ Suborder Patellina

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★ Superfamily Patelloidea

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★ Family Patellidae

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★ Genus ''Cellana''

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★ ''Cellana ampla''

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★ ''Cellana ardosioea'' Hombron & Jacquinot, 1841

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★ ''Cellana capensis'' Gmelin, 1791

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★ ''Cellana craticulata'' Suter, 1905

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★ ''Cellana conciliata'' Rainbow limpet

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★ ''Cellana denticulata'' Martyn, 1784

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★ ''Cellana eucosmia'' Pilsbry, 1891

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★ ''Cellana exarata'' Hawaiian blackfoot ''‘opihi''

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★ ''Cellana flava'' Hutton, 1873

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★ ''Cellana grata'' Gould, 1859

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★ ''Cellana melanostoma'' Pilsbry, 1891

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★ ''Cellana nigrolineata'' Reeve, 1854

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★ ''Cellana ornata'' Dillwyn, 1817

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★ ''Cellana radians'' (Gmelin, 1791)

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★ ''Cellana rota''

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★ ''Cellana sandwicensis''

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★ ''Cellana stellifera'' Gmelin, 1791

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★ ''Cellana strigilis'' Powell, 1955

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★ ''Cellana strigilis strigilis'' Hombron & Jacquinot, 1841

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★ ''Cellana strigilis bollonsi'' Powell, 1955

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★ ''Cellana strigilis chathanensis'' (Pilsbry, 1891

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★ ''Cellana strigilis flemingi'' Powell, 1955

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★ ''Cellana strigilis oliveri'' Powell, 1955

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★ ''Cellana strigilis redimiculum'' (Reeve, 1854)

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★ ''Cellana talcosa'' Gould, 1846

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★ ''Cellana testudinaria'' Linnaeus, 1758

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★ ''Cellana toreuma'' Reeve, 1855

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★ ''Cellana tramoserica'' Holten, 1802

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★ Genus ''Helcion''

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★ Subgenus ''Ansates''

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★ ''Helcion pellucidus''

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★ ''Helcion tella''

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★ Subgenus ''Helcion''

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★ ''Helcion pectunculus''

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★ Subgenus ''Patinastra''

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★ ''Helcion dunkeri''

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★ ''Helcion pruinosus''

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★ Genus ''Helioniscus''

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★ ''Helcion tella''

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★ Genus ''Patella''

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★ Subgenus ''Olana''

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★ ''Patella cochlear''

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★ Subgenus ''Patella''

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★ ''Patella baudonii''

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★ ''Patella caerulea''

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★ ''Patella candei''

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★ ''Patella (candei) gomesii''

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★ ''Patella compressa''

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★ ''Patella depressa''

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★ ''Patella ferruginea''

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★ ''Patella lowei''

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★ ''Patella miniata''

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★ ''Patella moreleti''

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★ ''Patella piperata''

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★ ''Patella rustica''

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★ ''Patella ulyssiponensis''

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★ ''Patella variabilis''

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★ ''Patella vulgata''

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★ ''Patellida''

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★ ''Patella granularis''

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★ ''Patellona''

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★ ''Patella adansonii''

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★ ''Patella canescens''

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★ ''Patella granatina''

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★ ''Patella lugubris''

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★ ''Patella oculus''

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★ ''Patella plumbea''

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★ ''Scutellastra''

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★ ''Patella argenvillei''

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★ ''Patella barbara''

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★ ''Patella chapmani''

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★ ''Patella exusta''

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★ ''Patella flexuosa''

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★ ''Patella kermadecensis''

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★ ''Patella laticostata''

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★ ''Patella longicosta''

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★ ''Patella peronii''

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★ ''Patella tabularis''

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★ ''Patella tucopiana''

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★ Genus ''Rhodopetala''

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★ ''Rhodopetala rosea''

References

★ University of Hawaii Educational page from Christopher F. Bird, Dep't of Botany. Photos and detailed information distinguishing the different varieties.

★ Acmaeidae at the NCBI taxonmy website