Sea snail

This article is about shelled gastropods that live in salt water. For the fish which are also sometimes known as "snails", seeSnailfish.

A species of sea snail in its natural habitat: two individuals of thewentletrapEpidendrium billeeanumwith a mass of egg capsulesin situon their food source, a red cupcoral.

Sea snailis acommon namefor slow-movingmarinegastropodmolluscs,usually with visible external shells, such aswhelkorabalone.They share thetaxonomic classGastropodawithslugs,which are distinguished fromsnailsprimarily by the absence of a visibleshell.

Definition

Determining whether some gastropods should be called sea snails is not always easy. Some species that live inbrackish water(such as certainneritids) can be listed as eitherfreshwater snailsor marine snails, and some species that live at or just above thehigh tidelevel (for example, species in the genusTruncatella) are sometimes considered to be sea snails and sometimes listed asland snails.

Anatomy

Sea snails are a very large and diverse group of animals. Most snails that live insalt waterrespire using agillor gills; a few species, though, have a lung, areintertidal,and are active only at low tide when they can move around in the air. These air-breathing species include false limpets in the familySiphonariidaeand another group of false limpets in the familyTrimusculidae.

Many, but not all, sea snails have anoperculum.

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 oflimpets.In one unusual family (Juliidae), the shell of the snail has become two hinged plates closely resembling those of abivalve;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 fromSyrinx aruanus,the largest living shelled gastropod species at 91 cm (36 in), 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 thefossil record.

Theshells of snailsare 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 ofaragonitein the growth layers ofmollusksyou can predict the size the mollusk shell can reach.

Taxonomy

The shell ofSyrinx aruanuscan be up to 91 cm long.

A 50-second video of snails (most likelyNatica chemnitziandCerithiumstercusmuscaram) feeding on the sea floor in theGulf of California,Puerto Peñasco,Mexico.

Ahermit craboccupying a shell ofAcanthina punctulatahas been disturbed, and has retracted into the shell, using its claws to bar the entrance in the same way the snail used itsoperculum.

2005 taxonomy

The followingcladogramis an overview of the main clades of living gastropods based on thetaxonomy of Bouchet & Rocroi(2005),with taxa that contain saltwater or brackish water species marked inboldface(some of the highlighted taxa consist entirely of marine species, but some of them also contain freshwater or land species.)

• CladePatellogastropoda
• CladeVetigastropoda
• CladeCocculiniformia
• CladeNeritimorpha
  • CladeCycloneritimorpha
• CladeCaenogastropoda
  • Informal groupArchitaenioglossa
  • CladeSorbeoconcha
  • CladeHypsogastropoda
    • CladeLittorinimorpha
    • Informal groupPtenoglossa
    • CladeNeogastropoda
• CladeHeterobranchia
  • Informal groupLower Heterobranchia
  • Informal groupOpisthobranchia
    • CladeCephalaspidea
    • CladeThecosomata
    • CladeGymnosomata
    • CladeAplysiomorpha
    • GroupAcochlidiacea
    • CladeSacoglossa
    • GroupCylindrobullida
    • CladeUmbraculida
    • CladeNudipleura
      • CladePleurobranchomorpha
      • CladeNudibranchia
        • CladeEuctenidiacea
        • CladeDexiarchia
          • CladePseudoeuctenidiacea
          • CladeCladobranchia
            • CladeEuarminida
            • CladeDendronotida
            • CladeAeolidida
  • Informal groupPulmonata
    • Informal groupBasommatophora
    • CladeEupulmonata
      • CladeSystellommatophora
      • CladeStylommatophora
        • CladeElasmognatha
        • CladeOrthurethra
        • Informal groupSigmurethra

Uses

By humans

A number of species of sea snails are harvested inaquacultureand used by humans for food, includingabalone,conch,limpets,whelks(such as the North AmericanBusyconspecies and the North AtlanticBuccinum undatum) andperiwinklesincludingLittorina littorea.

The shells of sea snails are often found washed up onbeaches.Because many are attractive and durable, they have been used to make necklaces and otherjewelrysince prehistoric times.

The shells of a few species of large sea snails within theVetigastropodahave a thick layer ofnacreand have been used as a source ofmother of pearl.Historically, thebuttonindustry 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 ofhermit crabs.A hermit crab carries the shell by grasping the centralcolumellaof the shell using claspers on the tip of its abdomen.

See also

• Freshwater snail
• Terrestrial molluscs
• Land snail
• Sea slug