snail
DESCRIPTION
snailTRANSCRIPT
Snailis acommon namethat is applied most often toland snails,terrestrialpulmonategastropodmolluscs. However, the common name "snail" is also applied to most of the members of themolluscanclassGastropodathat have a coiledshellthat is large enough for the animal to retract completely into. When the word "snail" is used in this most general sense, it includes not just land snails but also thousands of species ofsea snailsandfreshwater snails. Occasionally a few other molluscs that are not actually gastropods, such as theMonoplacophora, which superficially resemble smalllimpets, may also informally be referred to as "snails".Snail-like animals that naturally lack ashell, or have only an internal shell, are usually calledslugs, and land snails that have only a very small shell (that they cannot retract into) are often calledsemislugs.Snail
Snails thatrespireusing alungbelong to the groupPulmonata, while those withgillsform apolyphyleticgroup; in other words, snails with gills form a number oftaxonomicgroups that are not necessarily more closely related to each other than they are related to some other groups. Both snails that have lungs and snails that have gills have diversified so widely over geological time that a few species with gills can be found on land and numerous species with lungs can be found in freshwater. Even a few marine species have lungs.Snails can be found in a very wide range of environments, includingditches,deserts, and theabyssaldepths of the sea. Althoughlandsnails may be more familiar to people,marinesnails constitute the majority of snail species, and have much greater diversity and a greaterbiomass. Numerous kinds of snail can also be found infresh water. Most snails have thousands of microscopic tooth-like structures located on a ribbon-like tongue called aradula. The radula works like a file, ripping food into small pieces. Many snails areherbivorous, eating plants or rasping algae from surfaces with their radulae, though a few land species and many marine species areomnivoresorpredatorycarnivores.Several species of the genusAchatinaand related genera are known as giant African land snails; some grow to 15in (38cm) from snout to tail, and weigh 1kg (2lb).[1]The largest living species of sea snail isSyrinx aruanus; its shell can measure up to 90cm (35in) in length, and the whole animal with the shell can weigh up to 18kg (40lb).