Sea snails are slow-moving marine gastropod Mollusca, usually with visible external shells, such as whelk or abalone. They share the taxonomic class Gastropoda with , which are distinguished from snails primarily by the absence of a visible Gastropod 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
Neritidae) 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
.
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
. 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 Gastropod shell 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.)
Uses
By humans
A number of species of sea snails are harvested in
aquaculture and used by humans for food, including
abalone,
conch,
,
(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 . Because many are attractive and durable, they have been used to make necklaces and other Shell 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.
Due to high calcium carbonate content, sea snail shells have potential to be used as raw material in the production of lime
By non-human animals
The shells of sea snails are used for protection by many kinds of
. A hermit crab carries the shell by grasping the central columella of the shell using claspers on the tip of its abdomen.
See also