Asnail is a shelledgastropod. The name is most often applied toland snails,terrestrialpulmonategastropodmolluscs. However, the common namesnail is also used for most of the members of the molluscan classGastropoda that have a coiledshell 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 ofsea snails andfreshwater snails. Gastropods that naturally lack a shell, or have only an internal shell, are mostly calledslugs, and land snails that have only a very small shell (that they cannot retract into) are often calledsemi-slugs.
Snails have considerable human relevance, includingas food items, as pests, and as vectors of disease, and their shells are used as decorative objects and are incorporated into jewellery.[1] The snail has also had some cultural significance, tending to be associated with lethargy. The snail has also been used as afigure of speech in reference to slow-moving things.
Snails thatrespire using alung belong to the groupPulmonata. As traditionally defined, the Pulmonata were found to bepolyphyletic in a molecular study per Jörgeret al., dating from 2010.[2] But snails withgills also form apolyphyletic group; in other words, snails with lungs and snails with gills form a number oftaxonomic 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, includingditches,deserts, and theabyssal depths of the sea. Althoughland snails may be more familiar to laymen,marine snails 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 banded 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 areomnivores orpredatorycarnivores. Snails cannot absorb colored pigments when eating paper or cardboard so their feces are also colored.[3]
Several species of the genusAchatina and related genera are known as giant African land snails; some grow to 38 cm (15 in) from snout to tail, and weigh 1 kg (2 lb).[4] The largest living species of sea snail isSyrinx 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). The smallest land snail,Angustopila psammion, was discovered in 2022 and measures 0.6 mm in diameter.[5]
The largest known land gastropod is the African giant snailAchatina 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 (about 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.[6]
Snails areprotostomes. That means during development, in thegastrulation phase, the blastopore forms the mouth first. Cleavage in snails is spiral holoblastic patterning. In spiral holoblastic cleavage, the cleavage plane rotates each division and the cell divisions are complete. Snails do not undergo metamorphosis after hatching. Snails hatch in the form of small adults. The only additional development they will undergo is to consume calcium to strengthen their shell. Snails can be male, female,hermaphroditic, orparthenogenetic so there are many different systems of sexual determination.
Snails have complex organ systems and anatomies that differ greatly from mostanimals. Snails and most otherMollusca share three anatomical features; the foot, themantle, and theradula.
Foot
The foot is a muscular organ used byGastropods forlocomotion. Gastropods'stomachs are located within their foot. Both land and sea snails travel by contracting foot muscles to deform themucus layer beneath it into different wave-like patterns.[7]
Mantle
The mantle is the organ that produces shells for most species of mollusca. In snails, the mantle secretes the shell along the snail shell opening, continuously growing and producing the shell for the entirety of the snail's life.[8] The mantle creates a compartment known as the mantle cavity and is used by many mollusca as the surface where gas exchange occurs. Snails that use the mantle cavity as alung are known asPulmonate snails. Other snails may only have agill. Snails in theCaenogastropoda families likeAmpullariidae, have both a gill and a lung.[9]
Snail shellSnail shells are mainly composed of a mixture of proteins calledconchin, andcalcium carbonate. Conchin is the main component in the outer layer of the shell, known as theperiostracum. The inner layers of the shell are composed of a network of calcium carbonate, conchin, and different mineral salts. The mantle produces the shell through addition around a central axis called thecolumella, causing a spiraling pattern.[10] The spiraling patterns on a snail's shell are known as coils orwhorls. Whorl size generally increases as the snail ages. Size differences in shell size are believed to be mainly influenced by genetic and environmental components. Moister conditions often correlate with larger snails. In larger populations, adult snails attain smaller shell sizes due to the effects ofpheromones on growth rate.[11]
Radula
The radula is an anatomical structure used by most species of Mollusca for feeding. Gastropods are morphologically highly variable and have diverse feeding strategies. Snails can beherbivores,detritivores,scavengers,parasites, ciliary feeders, or have highly specializedpredation.[12] Nearly all snails utilize a feeding apparatus including the oral structures of one or more jaws and the radula. The radula comprises a chitinous ribbon with teeth arranged in transverse and longitudinal rows.[13] The radula continually renews itself during the entire lifespan of a mollusk. The teeth and membrane are continuously synthesized in the radular sac and then shifted forward towards the working zone of the radula. The teeth harden and mineralize during their travel to the working zone. The presence of the radula is common throughout most snail species, but often differs in many characteristics, like the shape, size, and number ofodontoblasts that form a tooth.
The average snail's diet varies greatly depending on the species, including different feeding styles fromherbivores to highly specialized feeders andparasites.[14] Some snails like theEuglandina rosea, or rosy wolfsnail, arecarnivorous and prey on other snails.[15] However, most land snails are herbivores oromnivores.[16] Among land snails, there is also a large variation in preference for specific food. For example,Cepaea nemoralis, or the grove snail, prefers dead plant material over fresh herbs or grasses. Age may also impact food preference, with adult grove snails showing a significantly larger preference for dead plant material than juvenile grove snails.[17] Other snails, like the generalist herbivoreArianta arbustorum, or copse snail, choose their meals based on availability, consuming a mix ofarthropods, wilted flowers, fresh and decayed plant material, and soil.[18]
Generally, land snails are most active at night due to the damp weather. The humid nighttime air minimizes waterevaporation and is beneficial to land snails because their movement requiresmucus, which is mostly composed of water.[16] In addition to aiding movement, mucus plays a vital role in transporting food from thegill to the mouth, cleansing themantle cavity, and trapping food before ingestion.[19]
Gastropods that lack a conspicuous shell are commonly calledslugs rather than snails.[20] Some species of slug have a maroon-brown shell, some have only an internalvestige that serves mainly as a calcium lactate repository, and others have some to no shell at all. Other than that, there is littlemorphological 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 frommonophyletic; 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.[21]
Land snails are known as an agricultural and garden pest but some species are an edible delicacy and occasionally householdpets. In addition, their mucus can also be used for skin care products.[22]
There is 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 concentratedgarlic orwormwood 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 asdiatomaceous earth can also deter snails.[23]
Thedecollate snail (Rumina decollata) will capture and eat garden snails, and because of this it has sometimes been introduced as abiological 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.
Certain varieties of snails, notably the familyMuricidae, produce a secretion that is a color-fastnatural dye. The ancientTyrian purple was made in this way as were other purple and blue dyes.[24][25][26] 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.[27]
Throughout history, snails have been kept as pets. There are many famous snails such asLefty (Born Jeremy) and within fiction,Gary andBrian the snail.[28]
InFrench cuisine, edible snails are served for instance inEscargot à laBourguignonne. The practice of rearing snails for food is known asheliciculture. 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 ofhibernation 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 eaten as gourmet food, several species of land snails provide an easily harvested source ofprotein 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 inbanana 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. For example, inIndonesia, they are fried assatay, a dish known assate kakul. The eggs of certain snail species are eaten in a fashion similar to the waycaviar is eaten.[29]
InBulgaria, 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 areHelix lucorum andHelix pomatia.[citation needed]
Snails and slug species that are not normally eaten in certain areas have occasionally been used asfamine 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.[30]
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 thedeadly sin ofsloth.[31][32] InMayan mythology, the snail is associated with sexual desire, beingpersonified by the godUayeb.[33]
Snails were widely noted and used indivination.[31] TheGreek poetHesiod wrote that snails signified the time to harvest by climbing the stalks, while theAztec moon godTecciztecatl bore a snail shell on his back. This symbolised rebirth; the snail's penchant for appearing and disappearing was analogised with themoon.[34]
Dead Snail
Keong Emas (Javanese andIndonesian forGolden Snail) is a popularJavanesefolklore about a princess magically transformed and contained in agolden snail shell. The folklore is a part of popular JavanesePanji 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).
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 ofemail, which can be virtually instantaneous.
^Speiser, Bernhard; Rowell-Rahier, Martine (1991). "Effects of Food Availability, Nutritional Value, and Alkaloids on Food Choice in the Generalist Herbivore Arianta arbustorum (Gastropoda: Helicidae)".Oikos.62 (3):306–318.Bibcode:1991Oikos..62..306S.doi:10.2307/3545495.ISSN0030-1299.JSTOR3545495.
