Snail

For other uses, see Snail (disambiguation).

For sea snails, see Sea snail. For slugs, see Slug.

Helix pomatia, a species of land snail.

Helix pomatia sealed in its shell with a calcareous epiphragm.

Snail is a common name which is applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often applied to land snails than to those from the sea or freshwater. Snail-like animals that naturally lack a shell, or have only an internal shell, are often called slugs, and land species that have only a very small shell (that they cannot retract into) are called semislugs. Some organisms that are not gastropods, such as the monoplacophora, may informally be referred to as snails.

Overview

Snails that respire using a lung belong to the group Pulmonata, while those with gills form a paraphyletic group; in other words, snails with gills are divided into a number of taxonomic groups that are not very closely related. Snails with lungs and with gills have diversified widely enough over geological time that a few species with gills can be found on land, numerous species with a lung can be found in freshwater, and a few species with a lung can be found in the sea.

Snails can be found in a very wide range of environments including ditches, deserts, and the abyssal depths of the sea. Although many people are familiar with terrestrial snails, land snails are in the minority. Marine snails constitute the majority of snail species, and have much greater diversity and a greater biomass. Numerous kinds of snail can also be found in fresh waters. Most snails have thousands of microscopic tooth-like structures located on a ribbon-like tongue called a radula. The radula works like a file, ripping the food into small pieces. Many snails are herbivorous, eating plants or rasping algae from surfaces with the radula, though a few land species and many marine species are omnivores or predatory carnivores.

Several species of the genus Achatina and related genera are known as Giant African land snails; some grow to 15 in (38 cm) from snout to tail, and weigh 1 kilogram (2 lb).^{[citation needed]} The largest living species of sea snail is Syrinx aruanus which has a shell that can measure up to 90 cm (35 in) in length, and the whole animal with the shell can weigh up to 18 kg (40 lb).

Types of snails by habitat

Main articles: Land snail, Freshwater snail, and Sea snail

Slugs

Main article: Slug

Gastropod species which lack a conspicuous shell are commonly called slugs rather than snails, although, other than having a reduced shell or no shell at all, there are really no appreciable differences between a slug and a snail except in habitat and behavior. A shell-less animal is much more maneuverable and compressible, and thus even quite large land slugs can take advantage of habitats or retreats with very little space, squeezing themselves into places that would be inaccessible to a similar-sized snail, such as under loose bark on trees or under stone slabs, logs or wooden boards lying on the ground.

Taxonomic families of land slugs and sea slugs occur within numerous larger taxonomic groups of shelled species. In other words, the reduction or loss of the shell has evolved many times independently within several very different lineages of gastropods, thus the various families of slugs are very often not closely related to one another.

Snails in cuisine

Escargot cooked with garlic and parsley butter in a shell (with a €0.02 coin, approx 19 mm across, as a scale object).

French cooked snails

Land snails (Scutalus sp.) on a Moche pot, 200 AD. Larco Museum Collection, Lima, Peru.

Apart from being relished as gourmet food, several species of land snails provide an easily harvested source of protein to many people in poor communities around the world. Many land snails are valuable because they can feed on a wide range of agricultural wastes such as shed leaves in banana plantations. In some countries Giant African Land Snails are produced commercially for food. Land snails, freshwater snails and sea snails are all eaten in a number of countries (principally Spain, Philippines, Morocco, Nigeria, Algeria, France, Sicily, Portugal, Greece, Belgium, Vietnam, Laos, Cambodia, Cyprus, Ghana, Malta, Terai of Nepal, several regions of India, southwestern China and parts of the U.S.A.). In certain parts of the world snails are fried. For example, in Bali they are fried as satay, a dish known as sate kakul. The eggs of certain snail species are eaten in a fashion similar to the way caviar is eaten.

Apart from snails and slugs appearing in cuisine as luxuries, they have occasionally been used as famine food in historical times. Variants of the following event have occurred in Europe from time to time:

In a popular publication quoted below occurs the following notice of a well-known land mollusk, in connection with a traditionary story of the plague, which has long had general currency in Scotland: ‘In the woodlands, the more formidable black nude slug, the Anon or Limax den, will also be often encountered. It is a huge voracious creature, herbivorous, feeding, to Barbara’s astonishment, on tender plants; fruits, as strawberries, apples; and even turnips and mushrooms; appearing morning and evening, or after rain; suffering severely in its concealment in long droughts, and remaining torpid in winter. The gray field slug (Limax agrestis) is actually recommended to be swallowed by consumptive patients! In the town of Dundee there exists a strange traditionary story of the plague, connected with the conversion, from dire necessity of the Arionaten, or black slug, to a use similar to that which the luxurious Romans are said to have made of the great apple-snail. Two young and blooming maidens lived together at that dread time, like Bessie Bell and Mary Gray, in a remote cottage on the steep (indeed almost perpendicular) ascent of the Bonnetmaker’s Hill. Deprived of friends or support by the pestilence that walked at noonday, they still retained their good looks and healthful aspect, even when the famine had succeeded to the plague. The jaundiced eyes of the famine-wasted wretches around them were instantly turned towards the poor girls, who appeared to thrive so well whilst others were famishing. They were unhesitatingly accused of witchcraft, and had nearly fallen a prey to that terrible charge; for betwixt themselves they had sworn never to tell in words by what means they were supported, ashamed as they felt of the resource to which they had been driven; and resolved, if possible, to escape the anticipated derision of their neighbours on its disclosure. It was only when about to be dragged before their stern inquisitors, that one of the girls, drawing aside the covering of a great barrel which stood in a corner of their domicile, discovered, without violating her oath, that the youthful pair had been driven to the desperate necessity of collecting and preserving for food large quantities of these Limacinoe, which they ultimately acknowledged to have proved to them generous and even agreeable sustenance. To the credit of the times of George Wishart—a glimpse of pre-reforming enlightenment—the explanation sufficed; the young women escaped with their lives, and were even applauded for their prudence.

Agriculture

In addition to the farming of edible snails, they also impact agriculture as a pest. Snails and slugs destroy crops by eating roots, leaves, stems and fruits. They are able to abrade and consume a large variety of plants with the abrasive radula. Metaldehyde-containing baits are frequently used for snail control, though they should be used with caution as they are toxic to dogs and cats.

Cultural depictions

Due to its slowness, the snail has traditionally been seen as a symbol of laziness. In Christian culture, it has been used as a symbol of the deadly sin of sloth. Psalms 58:8 uses snail slime as a metaphorical punishment.

Snails were widely noted and used in divination. The Greek poet Hesiod wrote that snails signified the time to harvest by climbing the stalks, while the Aztec moon god Tecciztecatl bore a snail shell on his back. This symbolised rebirth; the snail's penchant for appearing and disappearing was analogised with the moon.

Professor Ronald Chase of McGill University in Montreal has suggested that the ancient myth of Cupid's arrows might be based on early observations of the love dart behavior of the land snail species Helix aspersa.

In contemporary speech, the expression "a snail's pace" is often used to describe a slow, inefficient process. The phrase "snail mail" is used to mean regular postal service delivery of paper messages as opposed to the delivery of e-mail or electronic mail, which can be virtually instantaneous.

See also

• Escargot de Quimper
• Gastropod shell
• Pasilalinic-sympathetic compass