A causa della sua lentezza, la chiocciola è sempre stata vista come un simbolo di pigrizia.
Venivano utilizzate per la divinazione, per gli Aztechi era il simbolo della rinascita.FONTE:
From Wikipedia, the free encyclopedia
Snail is a common name for almost all members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in a general sense, it includes sea snails, land snails and freshwater snails. Otherwise snail-like creatures that lack a shell (or have only a very small one) are called slugs.
One species of land snail, the three species of Giant African land snail, can grow to be 15 in (38 cm) from snout to tail, and weigh 1 kilogram (2 lb). 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).
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.
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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.
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.
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.
Brian the Snail was a regular character in the popular children's television series The Magic Roundabout.
In the animated American TV series SpongeBob SquarePants, the main character has a pet called Gary the Snail. This snail makes a meow vocalization like a cat.
^ "Pests in Gardens and Landscapes". University of California, Davis. Retrieved 2010-08-03.
^ a b de Vries, Ad (1976). Dictionary of Symbols and Imagery. Amsterdam: North-Holland Publishing Company. p. 430. ISBN 0-7204-8021-3.
^ Jack Tresidder, Symbols and Their Meanings, New York: Barnes & Noble, 2006, ISBN 9780760781647, p. 41.
^ Cooper, JC (1992). Symbolic and Mythological Animals. London: Aquarian Press. p. 213. ISBN 1-85538-118-4.
^ "Lovebirds and Love Darts: The Wild World of Mating". news.national-geographic.com. National Geographic Society. Retrieved 2010-02-21.FONTE:
From Wikipedia, the free encyclopedia
A land snail is any of the many species of snail that live on land, as opposed to those that live in salt water and fresh water. Land snails are terrestrial gastropod molluscs that have shells; (those without shells are known as slugs.)
The majority of land snails are pulmonates, i.e. they have a lung and breathe air. A minority however belong to much more ancient lineages where their anatomy includes a gill and an operculum. Many of these operculate land snails live in habitats or microhabitats that are sometimes or often damp or wet, such as for example in moss.
It is not always easy to draw the line as to what species are land snails. There are some species that are more or less amphibious between land and freshwater, and others that are relatively amphibious between land and saltwater.
Land snails move by gliding along on their muscular foot, which is lubricated with mucus and covered with epithelial cilia. This motion is powered by succeeding waves of muscular contractions that move down the ventral 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). Snails secrete mucus to keep their soft bodies from drying out. They also secrete mucus from the foot to aid in locomotion by reducing friction, and to help reduce the risk of mechanical injury from sharp objects, meaning they can crawl over a sharp edge like a straight razor and not be injured. The mucus that land snails secrete with the foot leave a slime trail behind them, which is visible as a shiny "path" on the surface over which they have crawled. Snails (like all mollusks) also have a mantle, a specialized layer of tissue which covers all of the internal organs as they are grouped together in the visceral mass. The mantle also extends outward in flaps which reach to the edge of the shell and in some cases can cover the shell, and which are partially retractable. The mantle is attached to the shell, and creates the shell and makes shell growth possible by secretion.
Most molluscs, including land snails, have a shell which is part of their anatomy since the larval stage, and which grows with them in size by the process of secreting calcium carbonate along the open edge and on the inner side for extra stength. Although some land snails create shells that are almost entirely formed from the protein conchiolin, most land snails need a good supply of 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.
When retracted into their shells, many snails with gills (including some terrestrial species) are able to protect themselves with a door-like anatomical structure called an operculum.
Land snails range greatly in size. The largest living species is the Giant African Snail or Ghana Tiger Snail (Achatina achatina; Family Achatinidae), which can measure up to 30 cm.
Most land snails bear one or two pairs of tentacles on their heads. In most land snails the eyes are carried on 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 olfactory organs. Both sets of tentacles are retractable in land snails.
FONTE IMMAGINE: http://en.wikipedia.org/wiki/File:Snail_climbing_grass_SMC_07.jpg
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 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 associative learning.
Growth of the shell
As the snail grows, so does its calcium carbonate shell. The shell grows additively, by the addition of new calcium carbonate, which is secreted by glands located in the snail's mantle. The new material is added to the edge of the shell aperture (the opening of the shell). Therefore the centre of the shell's spiral was made when the snail was younger, and the outer part when the snail was older. When the snail reaches full adult size, it may build a thickened lip around the shell aperture. At this point the snail stops growing, and begins reproducing.
A snail's shell forms a logarithmic spiral. Most snail shells are right-handed, meaning that if the shell is held with the apex (the tip, or the juvenile whorls) pointing towards the observer, the spiral proceeds in a clockwise direction from the apex to the opening.
Hibernation and estivation
Some snails hibernate during the winter (typically October through April in the Northern Hemisphere). They may also estivate in the summer in drought conditions. If snails are not able to hibernate, the snail can die or its species may even go extinct like the Aldabra banded snail.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.
FONTE IMMAGINE: http://en.wikipedia.org/wiki/File:Samsoncj_snail_07.jpg
The great majority of land snails are hermaphrodites with a full set of reproductive organs of both sexes, able to produce both spermatozoa and ova. A few groups of land snails such as the Pomatiidae which are distantly related to periwinkles, have separate sexes; they are male and female. The age of sexual maturity is variable depending on species of snail, ranging from as little as 6 weeks  to 5 years. Adverse environmental conditions may delay the onset of sexual maturity in some snails.
Prior to reproduction, most pulmonate land snails perform courtship behaviors before mating. The courtship may last anywhere between two and twelve hours.
Prolific breeders, pulmonate land snails inseminate each other in pairs to internally fertilize their ova via 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. Fertilization then occurs and the eggs develop. Each brood may consist of up to 100 eggs.
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 mm 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. The cannibalization by baby snails of other eggs, even unhatched ones, has been recorded. Promptly after they are finished ingesting their egg casings, they crawl upwards through the small tunnel in order to digest the egg. 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 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.
There have been hybridizations of snails; although these do not occur commonly in the wild, in captivity they can be coaxed into doing so.
Parthenogenesis has also been noted in certain species.
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The lifespan of land snails varies from species to species. In the wild, Achatinidae snails live around 5 to 7 years and Helix snails live about 2 to 3 years. 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 25 years.
In the wild, snails eat a variety of different foods. Terrestrial snails are usually herbivorous, however there are some species that are predatory carnivores or omnivores. The diet of most land snails can include leaves, stems, soft bark, fruit, vegetables, fungi and algae. Some species can cause damage to agricultural crops and garden plants, and are therefore often regarded as pests.
FONTE IMMAGINE: http://commons.wikimedia.org/wiki/File:Closeup_of_snail_in_fishtank.jpg