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Snail
The word '''snail''' is a common name that can be used for almost all members of the molluscan class Gastropoda which have coiled animal shell|shells in the adult stage. (Those snails which do not have a shell or only a very small shell are usually called slugs. Snails which have a broadly conical shell which is not coiled, or appears not to be coiled, are often known as limpets.) When the word snail is used in a general sense, it includes sea snails, land snails and freshwater snails.
The class of Gastropoda (the snails and slugs) is second only to the insects in terms of total number of species. Snails are extraordinarily diverse in habitat, morphology (biology)|form, ethology|behavior, and anatomy, and therefore what is true of one snail species may not at all be true of another.
Snails can be found in a wide range of different and alike environments from ditches to deserts to the abyssal zone|abyssal depths of the sea. The great majority of snail species are marine biology|marine. Many others are terrestrial ecoregion|terrestrial, and numerous kinds can be found in fresh water, and even brackish water. Many snails are herbivore|herbivorous, though a few land species and many marine species are omnivores or predation|predatory carnivores.
Although the average person might perhaps be more familiar with terrestrial snails, land snails are in the minority. Marine snails have much greater diversity, and a greater biomass (ecology)|biomass. Snails which respiration (physiology)|respire using a lung belong to the group Pulmonata, while those with gills form a paraphyly|paraphyletic group, in other words, snails with gills are divided into a number of taxonomy|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.
Although the word snail is often used for all shelled gastropods, the word "snail" can also be used in a much more limited sense, to mean various larger species of air-breathing (pulmonate) land snails. The majority of this article is about air-breathing land snails.
Land snails
Species of land snails live in almost every kind of habitat, from deserts and mountains to marshes, woodland, and gardens. However, certain species are ":wiktionary:anthropophilic|anthropophilic", which means they are found most often around human habitation.
Whichever reasonably large land snail species is most commonly seen or most commonly eaten in a given area, that species will usually be referred to simply as "snails" by the local people. In many parts of the world, the fairly large edible species ''Helix aspersa'' or ''Cornu aspersum'', has been introduced, and has become a pest (organism)|pest in agriculture|farms and gardens, so this is perhaps a good example of a species commonly known as "the snail".
Slugs
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 thus even quite large land slugs can take advantage of habitats or retreats with very little space – places that would be totally 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.
Biology (primarily but not exclusively of pulmonate land snails)
Physical characteristics
Most snails move by gliding along on their muscular foot, which is lubricated with mucus. This motion is powered by succeeding waves of muscular contraction which move down the undersurface of the foot. This muscular action is clearly visible when a snail is crawling on the glass of a window or aquarium. Snails move at a proverbially low speed (1 mm/s is a typical speed for adult ''Helix lucorum''[
]). They produce mucus in order to aid locomotion by reducing friction, and the mucus also helps reduce the snail's risk of mechanical injury from sharp objects. This means that they can 'walk' over sharp objects like razors without being injured.[Conchologists of America FAQ no. 6] and 18 kg (40lbs) in weight.[Fun Animal Facts]
As the snail grows, so does its calcium carbonate shell. A snail's shell forms a logarithmic spiral. Most snail shells are right-handed, meaning that if you hold the shell with the apex (the tip, or the juvenile whorls) pointing towards you, then the spiral proceeds in a clockwise direction from the apex to the opening. When the animal reaches full adult size, many species of snails build a thickened lip around the opening of the shell. At this point the animal stops growing, and begins reproducing.
The shells of snails and other molluscs, and some snail egg casings, are primarily made up of calcium carbonate. Because of this, molluscs need calcium in their diet and environment to produce a strong shell. A lack of calcium, or low pH in their surroundings, can result in thin, cracked, or perforated shells. Usually a snail can repair damage to its shell over time if its living conditions improve, but severe damage can be fatal.
Most snails bear one or two pairs of tentacles on their heads. In most Stylommatophora|land snails the eyes are carried on the base of the first (upper) set of tentacles (called ommatophores or more informally 'eye stalks') which are usually roughly 75% of the width of the eyes. The second (lower) set of tentacles act as olfaction|olfactory organs. Both sets of tentacles are retractable in Stylommatophora|land snails. The eyes of most marine and freshwater snails are found at the base of the first set of tentacles.
Internal anatomy (land snails)
A snail breaks up its food using the radula, which is a chitinous structure containing microscopic hooks called cuticulae. With this the snail scrapes at food, which is then transferred to the digestive tract. This is why, in a quiet setting, a large land snail can be heard 'crunching' its food: the radula is tearing away at what it is eating.
The cerebral ganglion|ganglia of the snail form a primitive brain divided into four sections. This structure is very much simpler than the brains of mammals, reptiles and birds, but nonetheless, snails are capable of classical conditioning|associative learning.Hibernation/Estivation (land snails)
Some snails hibernation|hibernate during the winter (typically October through April in the Northern Hemisphere). They may also estivation|estivate in the summer in drought conditions. To stay moist during hibernation, a snail seals its shell opening with a dry layer of mucus called an ''epiphragm''.
Some freshwater snails such as apple snails have gills and a "door" or operculum to close the shell when they withdraw. This structure functions as protection from predators as well as protecting the soft tissues from desiccation when an aquatic habitat dries out temporarily.
Reproduction (primarily land snails)
All land snails are hermaphrodites, producing both spermatozoon|spermatozoa and ovum|ova. Some freshwater snails, such as Apple Snails, and marine species, such as periwinkles, have separate sexes; they are male and female. Most snails can mate when they are around 1 year old.[Snails]
Prior to reproduction, most land snails perform a ritual courtship before mating. This may last anywhere between two and twelve hours. Prolific breeders, pulmonate land snails insemination|inseminate each other in pairs to internal fertilization|internally fertilize their ova. Each brood may consist of up to 100 egg (biology)|eggs.
Pulmonate land snails and slugs have a reproductive opening on one side of the body, near the front, through which the outer reproductive organs are extruded so that exchange of sperm can take place. After this, fertilization occurs and the eggs develop.
Garden snails bury their eggs in shallow topsoil primarily while the weather is warm and damp, usually 5 to 10 cm down, digging with their foot. Egg sizes differ between species, from a 3 mm diameter in the grove snail to a 6 cm diameter in the Giant African Land Snail. After 2 to 4 weeks of favorable weather, these eggs hatch and the young emerge. Snails may lay eggs as often as once a month.
The snail's shell develops while it is still an embryo; it is, however, very weak, and needs an immediate supply of calcium. Newly hatched snails obtain this by eating the egg from which they hatched. Baby snails cannibalizing other eggs, even unhatched ones, has been recorded. Promptly after they are finished ingesting their egg casings, they crawl upwards through the small tunnel remaining from when their parent dug their nest. At this stage, the young are almost completely transparent and colorless. Their shell is usually slightly smaller than the egg they hatched from, but their niglets length when out of their shell is slightly greater than the egg diameter. After a few weeks, the snails will begin to show their first tinge of color, usually slightly blue, before they turn their adult color. Roughly three months after they have hatched, they will look like miniature versions of their mature kin. They will continue to grow, usually for two to three years, until they reach adult size, although there have been confirmed recordings of snails growing amazingly fast - becoming even bigger than their parents in little more than a month. Irrespective of their rate of growth, however, it will still take at least 1 year before they are sexually mature.[www.blackwell-synergy.com/doi/pdf/10.1111/j.1420-9101.2004.00791.x][http://links.jstor.org/sici?sici=0014-3820(199208)46%3A4%3C907%3APIAFSR%3E2.0.CO%3B2-F]
Freshwater pond snails do not lay their eggs in the ground, but instead they attach them to something solid, or in some genera they carry the eggs internally until they hatch, a form of vivipary.
Lifespan
The lifespan of snails varies from species to species. In the wild, Achatinidae snails live around 5 to 7 years and Helix (genus)|Helix snails live about 2 to 3 years. Aquatic Apple Snails live only a year or so. Most deaths are due to predators or parasites. In captivity, their lifespan is much longer, ranging from 10 to 15 years for most species. On occasions, snails have lived beyond this lifespan, up to 30 years.[The Roman snail or escargot (''Helix pomatia'')]
Diet
In the wild, snails eat a variety of different foods. Terrestrial snails are herbivorous. Their diet can include leaves, stems, soft bark, fruit,vegetables and algae. Some species can cause damage to agriculture|agricultural crops and gardening|garden plants, and are therefore often regarded as pest (organism)|pests. Aquatic snails eat other varieties of food such as plankton, algae, plants, and other microorganism|microscopic organisms that live underwater.
Predators
Land snails have many natural predators, including members of all major vertebrate groups, decollate snails, ground beetles, leeches, and even the predatory caterpillar ''Hyposmocoma molluscivora''. The Botia family of freshwater fish also feed on freshwater snails by sucking them out of their shells.
In the pulmonate marsh snail, ''Succinea putris'', there is a parasitic flatworm, ''Leucochloridium paradoxum'', which prevents the snail from retracting its enlarged and parasitized eye stalk, which thus makes the snail much more likely to be eaten by a bird, its final host.
Humans also pose great dangers to snails in the wild. Pollution and the destruction of habitats has caused the extinction of a number of snail species in recent years.[Centre for Biological Diversity: snail extinction update][ Hawaii's Extinct Species – Snails]
Snails in cuisine
Snails have been eaten for thousands of years, beginning in the Pleistocene. They are especially abundant in Capsian sites in North Africa but are also found throughout the Mediterranean Basin|Mediterranean region in archaeological sites dating between 12,000 and 6,000 years ago.[Prehistoric edible land snails in the circum-Mediterranean: the archaeological evidence.,
D. Lubell. In J-J. Brugal & J. Desse (eds.), ''Petits Animaux et Sociétés Humaines. Du Complément Alimentaire Aux Ressources Utilitaires''. XXIVe rencontres internationales d'archéologie et d'histoire d'Antibes, pp. 77-98. Antibes: Éditions APDCA.] ][Are land snails a signature for the Mesolithic-Neolithic transition? In, M. Budja (ed.), ''Neolithic Studies 11. Documenta Praehistorica XXXI'': 1-24. D. Lubell.] However, it should be noted that wild-caught land snails that are undercooked can harbor a parasite (Angiostrongylus cantonensis) that may cause a rare kind of meningitis.[ Division of Parasitic Diseases - Angiostrongylus Infection Fact Sheet] Specialized snail caviar is also growing in popularity in European cuisine.[ Snail caviar! The new gourmet frontier]
Europe
Snails are eaten in several European countries, as they were in the past in the Roman Empire. Mainly three species, all from the genus ''Helix (genus)|Helix'', are ordinarily eaten:
- ''Helix pomatia'', or ''edible snail'', generally prepared in its shell, with parsley butter (size: 40 to 55 mm for an adult weight of 25 to 45 g.; typically found in Burgundy, France).
- ''Helix aspersa'':
- ''Helix aspersa aspersa'' also known as the European brown snail, is cooked in many different ways, according to different local traditions (size: 28 to 35 mm for an adult weight of 7 to 15 g.; typically found in the Mediterranean countries of Europe and North Africa and the French Bay of Biscay|Atlantic coast).
- ''Helix aspersa maxima'' (size 40 to 45 mm for an average weight of 20 to 30 g.; typically found in North Africa).
Snails are a delicacy in French cuisine, where they are called ''escargot''. In an English-language menu, ''escargot'' is generally reserved for snails prepared with traditional French recipes (served in the shell with a garlic and parsley butter).Before preparing snails to eat, the snails should be fasting for three days with only water available. After three days of fasting, the snails should be fed flour and offered water for at least a week.This process is thought to cleanse the snails.
Snails are also popular in Portuguese cuisine (although not in the Portugal, Norte|north of the country) where they are called in Portuguese language|Portuguese ''caracóis'', and served in cheap snack houses and taverns, usually stewed (with different mixtures of white wine, garlic, piri piri, oregano, coriander or parsley, and sometimes chouriço). Bigger varieties, called ''caracoletas'', are generally grilled and served with a butter sauce, but other dishes also exist such as ''feijoada de caracóis''. Overall, Portugal consumes about 4,000 tonnes of snails each year.[According to the article ''Comemos três a quatro mil toneladas de caracóis por ano'', by Joana Ferreira da Costa, in the 26.08.2007 edition (n.6358) of the daily newspaper Público.]
Traditional Spanish cuisine also uses snails ("caracoles"), consuming several species such as ''Helix aspersa'', ''Helix punctata'', ''Helix pisana'' or ''Helix alonensis'' among others. Small to medium-size varieties are usually cooked in several spicy sauces or even in soups, while the bigger ones may be reserved for other dishes such as the "arroz con conejo y caracoles" (a paella-style rice with snails and Rabbit#Rabbits as food and clothing|rabbit meat, very popular in the inner regions of south-eastern Spain). Snails are very popular in Catalonia, where they are called "caragols" or "cargols." In fact, a snail celebration, the "Aplec del cargol," takes place in Lleida each May, drawing more than 200,000 visitors from abroad. Popular Catalonian recipes for snails are ''a la llauna'', grilled inside their own shells and then eaten after dipping them in garlic mayonnaise, or ''a la gormanda'', boiled in tomato and onion sauce.
In Greece, snails are especially popular in the island of Crete, but are also eaten in many parts of the country and can even be found in supermarkets, sometimes placed alive near partly refrigerated vegetables. In this regard, snails are one of the few live organisms sold at supermarkets as food. They are eaten either boiled with vinegar added, or sometimes cooked alive in a casserole with tomato, potatoes and squash (plant)|squashes. Limpets and sea snails also find their way to the greek table around the country. Another snail cooking method is the ''Kohli Bourbouristi'' (''χοχλιοί μπου(ρ)μπουριστοί'')[Popping Fried Snails - Kohli Bourbouristi Recipe] a traditional Cretan dish, which consists of fried snails in olive oil with lemon.
In Sicily, snails (or ''babbaluci'' as they are commonly called in Sicilian language|Sicilian) are a very popular dish as well. They are usually boiled with salt first, then served with tomato sauce or bare with oil, garlic and parsley. Snails are similarly appreciated in other Italian regions, such as Sardinia.
In southwestern Germany there is a regional specialty of soup with snails and herbs, called "Black Forest Snail Chowder" (''Badener Schneckensuepple'').
Heliciculture is the farming of snails. "They are protected in the wild almost everywhere (at least, the Roman Snail must not be collected any more), but the Roman Snail and the Garden Snail (''Cornu aspersum'') especially are cultivated on snail farms."Elsewhere
Achatina fulica, the Giant East African Snail, is sliced and canned and sold to consumers as escargot.
In parts of West Africa, specifically Ghana, snails are served as a delicacy. ''Achatina achatina'', Ghana tiger snails, are also known as some of the largest snails in the world.
Various snail species are eaten in Asian cuisines as well.
Cultural depictions
Due to its slowness, the snail has traditionally been seen as a symbol of laziness. In Judeo-Christian culture, it has often been viewed as a manifestation of the Seven deadly sins|deadly sin of Sloth (deadly sin)|sloth.Gallery
Image:Mochesnail.jpg|Moche land snails (''Scutalus Sp''.), 200 AD. Larco Museum|Larco Museum Collection, Lima, Peru.
Image:Snail2.JPG|''Cornu aspersa'', the Garden snail, in the USA
Image:GardenSnail1.jpg|''Cornu aspersa'', the Garden snail, Hampshire, UK
Image:European brown snail.jpg|''C. aspersa'', a brown Garden snail from Europe
Image:Gardensnail.jpg|''C. aspersa'', Garden snail from England
Image:Snail in pool with reflection.png|''C. aspersa'' in a pool of water
Image:Snail-WA edit02.jpg|White-lipped snail (''Cepaea hortensis'')
Image:Snail WA.jpg|White-lipped snail (''Cepaea hortensis'')
Image:Cepaea_nemoralis_pair_banded_shells.jpg|Two grove snails, ''Cepaea nemoralis''
Image:Snails mating 2996 05 02.jpg|Two grove snails, ''C. nemoralis'', mating
Image:Achatina fulica Thailand.jpg|Giant East African Snail (''Achatina fulica'')
Image:Pouch-snail.JPG|Freshwater snail in the genus ''Physa'', the pouch snail
Image:Kadina-snails-climb-fence-0716.jpg|The introduced snail ''Theba pisana'' in Kadina, South Australia[Common white snail]
See also
- Slug
- Snail racing
- Pasilalinic-sympathetic compass
- Love dart
References
External links
- predatory snails on the University of Florida|UF / Institute of Food and Agricultural Sciences| IFAS Featured Creatures Web site.
Category:Gastropods
simple:Snail
Related Images- The anatomy of a common snail
- right
- Two Helicid snails make contact prior to mating.
- Two ''Cornu aspersa'' Garden snails mating
- The egg mass of a freshwater pulmonate snail, attached to a solid surface.
- Freshwater species mating
- Cooked French Escargots
Sources: StartLearningNow, Wikipedia | Usage license: GNU FDL
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