Snail

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Snails
Snail.jpg
Helix pomatia , a species of land snail
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Mollusca
Class: Gastropoda
Helix pomatia sealed in its shell with a calcareous epiphragm Epiphragma einer Weinbergschnecke.JPG
Helix pomatia sealed in its shell with a calcareous epiphragm

A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name snail is also used for most of the members of the molluscan class Gastropoda that have a coiled shell that 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 numerous species of sea snails and freshwater snails. Gastropods that naturally lack a shell, or have only an internal shell, are mostly called slugs , and land snails that have only a very small shell (that they cannot retract into) are often called semi-slugs .

Contents

Snails have considerable human relevance, including as food items, as pests, and as vectors of disease, and their shells are used as decorative objects and are incorporated into jewelry. [1] The snail has also had some cultural significance, tending to be associated with lethargy. The snail has also been used as a metaphor: someone who is not moving fast enough is "slow as a snail." The snail is the same or similar shape as the Cochlea. [2]

Overview

Video of snails (most likely Natica chemnitzi and Cerithium stercusmuscaram) feeding on the sea floor in the Gulf of California, Puerto Peñasco, Mexico, 50 sec
Video of snail after rain, 31 sec

Snails that respire using a lung belong to the group Pulmonata. As traditionally defined, the Pulmonata were found to be polyphyletic in a molecular study per Jörger et al., dating from 2010. [3] But snails with gills also form a polyphyletic group; in other words, snails with lungs and snails with gills form a number of taxonomic groups 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, including ditches, deserts, and the abyssal depths of the sea. Although land snails may be more familiar to laymen, 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 water.

Most snails have thousands of microscopic tooth-like structures located on a banded ribbon-like tongue called a radula. The radula works like a file, ripping food into small pieces. Many snails are herbivorous, eating plants or rasping algae from surfaces with their radulae, though a few land species and many marine species are omnivores or predatory carnivores. Snails cannot absorb colored pigments when eating paper or cardboard so their feces are also colored. [4]

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 kg (2 lb). [5] The largest living species of sea snail is Syrinx aruanus ; its shell 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). Recently, the smallest land snails, Angustopila dominikae, have been discovered in China, and measure 0.86mm long. [6]

Snail moving on a wet ground
Snail moving across leaves.

The snail Lymnaea makes decisions by using only two types of neurons: one deciding whether the snail is hungry, and the other deciding whether there is food in the vicinity. [7]

The largest known land gastropod is the African giant snail Achatina achatina, the largest recorded specimen of which measured 39.3 centimetres (15.5 in) from snout to tail when fully extended, with a shell length of 27.3 cm (10.7 in) in December 1978. It weighed exactly 900 g (2 lb). Named Gee Geronimo, this snail was owned by Christopher Hudson (1955–79) of Hove, East Sussex, UK, and was collected in Sierra Leone in June 1976. [8]

Diet

Snails feed at night. [9] They feed primarily on decaying organic matter. [9] Their diet also includes fungi, lichens, green foliage, worms, centipedes, insects, animal feces, carrion, and other slugs. [9] Some snails feed on other snails too. [9]

Types of snails by habitat

Slugs

Slug Slug 02.jpg
Slug

Gastropods that lack a conspicuous shell are commonly called slugs rather than snails. [10] Some species of slug have a maroon-brown shell, some have only an internal vestige that serves mainly as a calcium lactate repository, and others have some to no shell at all. Other than that there is little morphological difference between slugs and snails. There are however important differences in habitats and behavior.

A shell-less animal is much more maneuverable and compressible, so even quite large land slugs can take advantage of habitats or retreats with very little space, retreats that would be inaccessible to a similar-sized snail. Slugs squeeze themselves into confined spaces such as under loose bark on trees or under stone slabs, logs or wooden boards lying on the ground. In such retreats they are in less danger from either predators or desiccation. Those are often suitable places for laying their eggs.

Slugs as a group are far from monophyletic; scientifically speaking "slug" is a term of convenience with little taxonomic significance. The reduction or loss of the shell has evolved many times independently within several very different lineages of gastropods. The various taxa of land and sea gastropods with slug morphology occur within numerous higher taxonomic groups of shelled species; such independent slug taxa are not in general closely related to one another.

Human relevance

Cornu aspersum - garden snail Snail-wiki-120-Zachi-Evenor.jpg
Cornu aspersum – garden snail

Land snails are known as an agricultural and garden pest but some species are an edible delicacy and occasionally household pets. In addition, their mucus can also be used for skin care products.

In agriculture

There are a variety of snail-control measures that gardeners and farmers use in an attempt to reduce damage to valuable plants. Traditional pesticides are still used, as are many less toxic control options such as concentrated garlic or wormwood solutions. Copper metal is also a snail repellent, and thus a copper band around the trunk of a tree will prevent snails from climbing up and reaching the foliage and fruit. A layer of a dry, finely ground, and scratchy substance such as diatomaceous earth can also deter snails. [11]

The decollate snail (Rumina decollata) will capture and eat garden snails, and because of this it has sometimes been introduced as a biological pest control agent. However, this is not without problems, as the decollate snail is just as likely to attack and devour other gastropods that may represent a valuable part of the native fauna of the region.

As food

French cooked snails Cooked snails.JPG
French cooked snails

In French cuisine, edible snails are served for instance in Escargot à la Bourguignonne . The practice of rearing snails for food is known as heliciculture. For purposes of cultivation, the snails are kept in a dark place in a wired cage with dry straw or dry wood. Coppiced wine-grape vines are often used for this purpose. During the rainy period, the snails come out of hibernation and release most of their mucus onto the dry wood/straw. The snails are then prepared for cooking. Their texture when cooked is slightly chewy and tender.

As well as 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 many countries. In certain parts of the world, snails are fried as for example, in Indonesia, 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.[ citation needed ]

In Bulgaria, snails are traditionally cooked in an oven with rice or fried in a pan with vegetable oil and red paprika powder. Before they are used for those dishes, however, they are thoroughly boiled in hot water (for up to 90 minutes) and manually extracted from their shells. The two species most commonly used for food in the country are Helix lucorum and Helix pomatia .[ citation needed ]

Famine food

Snails and slug species that are not normally eaten in certain areas have occasionally been used as famine food in historical times. A history of Scotland written in the 1800s recounts a description of various snails and their use as food items in times of plague. [12]

Parasitic diseases

Snails can also be associated with parasitic diseases such as schistosomiasis, angiostrongyliasis, fasciolopsiasis, opisthorchiasis, fascioliasis, paragonimiasis and clonorchiasis, which can be transmitted to humans.

Cultural depictions

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

Symbolism

Because of 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. [13] [14] Psalms 58:8 uses snail slime as a metaphorical punishment. In Mayan mythology, the snail is associated with sexual desire, being personified by the god Uayeb. [15]

Divination and other religious uses

Snails were widely noted and used in divination. [13] 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. [16]

Love darts and Cupid

The use of love darts by the land snail Monachoides vicinus is a form of sexual selection Monachoides vicinus dart lateral.jpg
The use of love darts by the land snail Monachoides vicinus is a form of sexual selection

Professor Ronald Chase of McGill University in Montreal has suggested the ancient myth of Cupid's arrows might be based on early observations of the love dart behavior of the land snail species Cornu aspersum. [17]

Metaphor

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 email, which can be virtually instantaneous.

In medieval and Renaissance manuscripts snails are depicted as a comic relief due to the similarity between the armour of knights and the shell of snails [18] .

In Indonesian mythology

Dewi Sekartaji as Keong Emas Dewi Sekartaji Keong Emas.JPG
Dewi Sekartaji as Keong Emas

Keong Emas (Javanese and Indonesian for Golden Snail) is a popular Javanese folklore about a princess magically transformed and contained in a golden snail shell. The folklore is a part of popular Javanese Panji cycle telling the stories about the prince Panji Asmoro Bangun (also known as Raden Inu Kertapati) and his consort, princess Dewi Sekartaji (also known as Dewi Chandra Kirana).

Textiles

Certain varieties of snails, notably the family Muricidae, produce a secretion that is a color-fast natural dye. The ancient Tyrian purple was made in this way as were other purple and blue dyes. [19] [20] [21] The extreme expense of extracting this secretion is sufficient quantities limited its use to the very wealthy. It is such dyes as these that led to certain shades of purple and blue being associated with royalty and wealth. [22]

As pets

Throughout history, snails have been kept as pets. There are many famous snails such as Lefty (Born Jeremy) and within fiction, Gary and Brian the snail . [23]

See also

Related Research Articles

Seashell Hard, protective outer layer created by an animal that lives in the sea

A seashell or sea shell, also known simply as a shell, is a hard, protective outer layer usually created by an animal that lives in the sea. The shell is part of the body of the animal. Empty seashells are often found washed up on beaches by beachcombers. The shells are empty because the animal has died and the soft parts have been eaten by another animal or have decomposed.

Gastropoda Class of snails and slugs

The gastropods, commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda.

Ampullariidae Family of gastropods

Ampullariidae, common name the apple snails, is a family of large freshwater snails, aquatic gastropod mollusks with a gill and an operculum. This family is in the superfamily Ampullarioidea and is the type family of that superfamily.

Sea slug Group of marine invertebrates with varying levels of resemblance to terrestrial slugs

Sea slug is a common name for some marine invertebrates with varying levels of resemblance to terrestrial slugs. Most creatures known as sea slugs are actually gastropods, i.e. they are sea snails that over evolutionary time have either completely lost their shells, or have seemingly lost their shells due to having a greatly reduced or internal shell. The name "sea slug" is most often applied to nudibranchs, as well as to a paraphyletic set of other marine gastropods without obvious shells.

Opisthobranchia Informal group of gastropods

Opisthobranchs is now an informal name for a large and diverse group of specialized complex gastropods which used to be united in the subclass Opisthobranchia. That taxon is no longer considered to represent a monophyletic grouping.

Whelk A common name that is applied to various kinds of sea snail

Whelk is a common name that is applied to various kinds of sea snail. Although a number of whelks are relatively large and are in the family Buccinidae, the word whelk is also applied to some other marine gastropod species within several families of sea snails that are not very closely related.

Siphon (mollusc) Anatomical structure which is part of the body of some aquatic molluscs

A siphon is an anatomical structure which is part of the body of aquatic molluscs in three classes: Gastropoda, Bivalvia and Cephalopoda.

Mantle (mollusc) Part of the anatomy of molluscs

The mantle is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of flaps well beyond the visceral mass itself.

<i>Achatina fulica</i> Species of land snail

Achatina fulica is a species of large land snail that belongs in the family Achatinidae. It is also known as the Giant African land snail. It shares the common name "giant African snail" with other species of snails such as Achatina achatina and Archachatina marginata.

Terrestrial animal Animals living on land

Terrestrial animals are animals that live predominantly or entirely on land, as compared with aquatic animals, which live predominantly or entirely in the water, or amphibians, which rely on a combination of aquatic and terrestrial habitats. Terrestrial invertebrates include ants, flies, crickets, grasshoppers and spiders.

Sea snail Common name for snails that normally live in saltwater

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.

A molluscivore is a carnivorous animal that specialises in feeding on molluscs such as gastropods, bivalves, brachiopods and cephalopods. Known molluscivores include numerous predatory molluscs,, arthropods such as crabs and firefly larvae, and, vertebrates such as fish, birds and mammals. Molluscivory is performed in a variety ways with some animals highly adapted to this method of feeding behaviour. A similar behaviour, durophagy, describes the feeding of animals that consume hard-shelled or exoskeleton bearing organisms, such as corals, shelled molluscs, or crabs.

Land snail Common name for many species of snail

A land snail is any of the numerous species of snail that live on land, as opposed to the sea snails and freshwater snails. Land snail is the common name for terrestrial gastropod mollusks that have shells. However, it is not always easy to say which species are terrestrial, because some are more or less amphibious between land and fresh water, and others are relatively amphibious between land and salt water.

<i>Achatina achatina</i> Species of gastropod

Achatina achatina, commonly known as the Giant Ghana African snail, also known as the Giant African snail, giant tiger land snail, and gigantocochlea, is a species of large, air-breathing land snail, a terrestrial pulmonate gastropod mollusk in the family Achatinidae. The name "Achatina" is from "achates", Greek for agate. It shares the common name "giant African snail" with other species of snails such as Achatina fulica and Archachatina marginata.

Slug Shell-less terrestrial gastropod mollusc

Slug, or land slug, is a common name for any apparently shell-less terrestrial gastropod mollusc. The word slug is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced shell, or only a small internal shell, particularly sea slugs and semislugs.

Mollusca Large phylum of invertebrate animals

Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda. The members are known as molluscs or mollusks. Around 85,000 extant species of molluscs are recognized. The number of fossil species is estimated between 60,000 and 100,000 additional species. The proportion of undescribed species is very high. Many taxa remain poorly studied.

Euthyneura Clade of molluscs

Euthyneura is a taxonomic infraclass of snails and slugs, which includes species from freshwater, marine, aquatic and terrestrial gastropod mollusks in the clade Heterobranchia.

The respiratory system of gastropods varies greatly in form. These variations were once used as a basis for dividing the group into subclasses. The majority of marine gastropods breathe through a single gill, supplied with oxygen by a current of water through the mantle cavity. This current is U-shaped, so that it also flushes waste products away from the anus, which is located above the animal's head, and would otherwise cause a problem with fouling.

Nervous system of gastropods

The nervous system of gastropods consists of a series of paired ganglia connected by major nerve cords, and a number of smaller branching nerves. It is sometimes called ganglionic.

Freshwater snail Non-marine snail

Freshwater snails are gastropod mollusks which live in fresh water. There are many different families. They are found throughout the world in various habitats, ranging from ephemeral pools to the largest lakes, and from small seeps and springs to major rivers. The great majority of freshwater gastropods have a shell, with very few exceptions. Some groups of snails that live in freshwater respire using gills, whereas other groups need to reach the surface to breathe air. In addition, some are amphibious and have both gills and a lung. Most feed on algae, but many are detritivores and some are filter feeders.

References

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  20. Biggam, Carole P. (March 2006). "Whelks and purple dye in Anglo-Saxon England" (PDF). The Archeo+Malacology Group Newsletter (9).
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