Sea snail

Sea snail is a common name for slow-moving marine gastropod molluscs, usually with visible external shells, such as whelk or abalone. They share the taxonomic class Gastropoda with slugs, which are distinguished from snails primarily by the absence of a visible shell.
Definition
Determining whether some gastropods should be called sea snails is not always easy. Some species that live in brackish water (such as certain neritids) can be listed as either freshwater snails or marine snails, and some species that live at or just above the high tide level (for example, species in the genus Truncatella) are sometimes considered to be sea snails and sometimes listed as land snails.
Anatomy
Sea snails are a very large and diverse group of animals. Most snails that live in salt water respire using a gill or gills; a few species, though, have a lung, are intertidal, and are active only at low tide when they can move around in the air. These air-breathing species include false limpets in the family Siphonariidae and another group of false limpets in the family Trimusculidae.
Many, but not all, sea snails have an operculum.
Shell
The shells of most species of sea snails are spirally coiled. Some, though, have conical shells, and these are often referred to by the common name of limpets. In one unusual family (Juliidae), the shell of the snail has become two hinged plates closely resembling those of a bivalve; this family is sometimes called the "bivalved gastropods".
Their shells are found in a variety of shapes and sizes, but are normally very small. Those living species of sea snails range in size from Syrinx aruanus, the largest living shelled gastropod species at , to minute species whose shells are less than 1 mm at adult size. Because the shells of sea snails are strong and durable in many cases, as a group they are well represented in the fossil record.
The shells of snails are complex and grow at different speeds. The speed of growth is affected by a few variables such as the temperature of the water, depth of the water, food present for the snail, as well as isotopic oxygen levels. By looking at the composition of aragonite in the growth layers of mollusks you can predict the size the mollusk shell can reach.
Taxonomy
2005 taxonomy
The following cladogram is an overview of the main clades of living gastropods based on the taxonomy of Bouchet & Rocroi (2005), with taxa that contain saltwater or brackish water species marked in boldface (some of the highlighted taxa consist entirely of marine species, but some of them also contain freshwater or land species.)
Clade Patellogastropoda
Clade Vetigastropoda
Clade Cocculiniformia
Clade Neritimorpha
Clade Cycloneritimorpha
Clade Caenogastropoda
Informal group Architaenioglossa
Clade Sorbeoconcha
Clade Hypsogastropoda
Clade Littorinimorpha
Informal group Ptenoglossa
Clade Neogastropoda
Clade Heterobranchia
Informal group Lower Heterobranchia
Informal group Opisthobranchia
Clade Cephalaspidea
Clade Thecosomata
Clade Gymnosomata
Clade Aplysiomorpha
Group Acochlidiacea
Clade Sacoglossa
Group Cylindrobullida
Clade Umbraculida
Clade Nudipleura
Clade Pleurobranchomorpha
Clade Nudibranchia
Clade Euctenidiacea
Clade Dexiarchia
Clade Pseudoeuctenidiacea
Clade Cladobranchia
Clade Euarminida
Clade Dendronotida
Clade Aeolidida
Informal group Pulmonata
Informal group Basommatophora
Clade Eupulmonata
Clade Systellommatophora
Clade Stylommatophora
Clade Elasmognatha
Clade Orthurethra
Informal group Sigmurethra
Uses
By humans
A number of species of sea snails are harvested in aquaculture and used by humans for food, including abalone, conch, limpets, whelks (such as the North American Busycon species and the North Atlantic Buccinum undatum) and periwinkles including Littorina littorea.
The shells of sea snails are often found washed up on beaches. Because many are attractive and durable, they have been used to make necklaces and other jewelry since prehistoric times.
The shells of a few species of large sea snails within the Vetigastropoda have a thick layer of nacre and have been used as a source of mother of pearl. Historically, the button industry relied on these species for a number of years.
By non-human animals
The shells of sea snails are used for protection by many kinds of hermit crabs. A hermit crab carries the shell by grasping the central columella of the shell using claspers on the tip of its abdomen.
See also
Freshwater snail
Terrestrial molluscs
Land snail
Sea slug
Slug
References
Mollusc common names
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