- For the world’s first commercial wave power device, see Islay LIMPET. For the underwater explosive device, see Limpet mine.
Limpet is a common name for a number of different groups of sea snails and freshwater snails (aquatic gastropod mollusks). The common name is applied to those snails that have a simple shell which is broadly conical in shape, and either is not spirally coiled, or appears not to be coiled in the adult snail. In other words the shell of all limpets is shaped more or less like that of most true limpets.
As well as being applied to the true limpets (the Patellogastropoda), the common name "limpet" is used for many other, widely different, snails, all of which have a shell that does not appear to be spirally coiled in the adult stage. The term "false limpets" is used for some of the other snails that have a shell that is limpet-like or "patelliform".
All the true limpets are marine, but the feature of a simple conical shell has arisen independently many times in gastropod evolution, in many different evolutionary lineages, and as a result, there are freshwater limpets and well as saltwater limpets. Some limpets have a gill or gills, some have a lung, and in some of those cases the lung has been modified to absorb oxygen from water. In other words, the name limpet is used to describe various extremely diverse groups of gastropods that have independently evolved a shell of the same basic shape (see convergent evolution).
Thus, although the name "limpet" is given on the basis of a limpet-like or "patelliform" shell, the several groups of snails that have a shell of this form are not at all closely related to one another:
- Clade Patellogastropoda, example Patellidae, the true limpets
- Clade Vetigastropoda, examples Fissurellidae the keyhole limpets and slit limpets, Lepetelloidea
- Clade Neritimorpha, example Phenacolepadidae, small limpets related to nerites
- Clade Heterobranchia, group Opisthobranchia, example Tylodinidae, the umbrella slugs
- Clade Heterobranchia, group Pulmonata, examples Siphonariidae, Latiidae, Trimusculidae
True limpets 
Other limpets 
- The keyhole limpets and slit limpets - Fissurellidae
- The hydrothermal vent limpets – Neomphaloidea and Lepetodriloidea
- The nerite limpets – Phenacolepadidae
- The hoof snails - Hipponix and other Hipponicidae
- Slipper snails - Crepidula species, which are sometimes known as slipper limpets
- Opisthobranch limpets such as Tylodina and also Umbraculum
- The pulmonate river and lake limpets - Ancylidae
Most of the marine limpets have gills, whereas all the freshwater limpets and a few of the marine limpets have a mantle cavity that is adapted to breathe air and function as a lung (and in some cases has been again adapted to absorb oxygen from water). All these various kinds of snail are only very distantly related.
||This article needs additional citations for verification. (April 2011)|
- University of Hawaii Educational page from Christopher F. Bird, Dep't of Botany. Photos and detailed information distinguishing the different varieties.
- Lottia gigantea: taxonomy, facts, life cycle, bibliography
- Acmaeidae at the NCBI taxonomy website