| vivint |
| vivint APX Alarms APX ALARM RIPS OFF THE PUBLIC, PEOPLE TOLD NO CONTRACT. CAN CANCEL AT ANY TIME. NO OBLIGATION. Provo, Utah |
| 22nd of Apr, 2011 by User339303 |
| Alarm sales man knocks on door, tells me he wants me to display a sign in my yard. In return for this i will be given an alarm system at no cost to me. I ask if this is a contract the sales man tells me NO!. He goes on to explain to me and my husband that we may cancel this at any given time so long as we continue to display the sign in the front yard for 42 months. My husband has now been made unemployed so naturally we wished to cancel the use of this service. On calling the support number we was told that to be able to cancel there was only two options open to us. The first was to get someone to take over the contract ( to this i asked what contract ) to this he answered the one you entered when you took the equipment. I was staggered and continued to argue about this to no avail. He said that maybe we could advertise it on Craig list and if we found someone to take the contract they would supply the people with a new system for their home. Option Two was to pay the remain of the contract which i might add does not end until 2014. I don't know if what they are doing is lawful. But its certainly a con. |
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Slug is a common name that is normally applied to any gastropod mollusk that lacks a shell, has a very reduced shell, or has a small internal shell. (This is in contrast to the common name snail, applied to gastropods that have a coiled shell large enough that the soft parts of the animal can retract fully into it.)
Slugs belong to several different lineages that also include snails with shells. The shell-less condition has arisen many times independently during the evolutionary past, and thus the category "slug" is emphatically a polyphyletic one. The various groups of land slugs are not closely related, despite a superficial similarity in the overall body form.
As well as land slugs, there are also many marine slugs and even one freshwater slug genus (Acochlidium, but the common name "slug" is most frequently applied to air-breathing land slugs, while the marine forms are usually known as sea slugs. Land gastropods with a shell that is not quite vestigial, but is too small to retract into (like many in the family Urocyclidae), are known as semislugs.
Slugs, like all other gastropods, undergo torsion (a 180º twisting of the internal organs) during development. Internally, slug anatomy clearly shows the effects of this rotation, but externally the bodies of slugs appear rather symmetrical, except for the positioning of the pneumostome, which is on one side of the animal, normally the right hand side.
The soft, slimy bodies of slugs are prone to desiccation, so land-living slugs are confined to moist environments and must retreat to damp hiding places when the weather is dry.
Contents [hide]
1 Morphology and behavior
2 Vestigial shell
3 Mucus
4 Reproduction
5 Ecology
6 Predators
7 Human relevance
8 Taxonomy
9 References
10 Further reading
11 External links
[edit]Morphology and behavior
Anatomy of a slug
Like other pulmonate land snails, most slugs have two pairs of 'feelers' or tentacles on their head. The upper pair is light sensing, while the lower pair provides the sense of smell. Both pairs are retractable, and can be regrown if lost.
On top of the slug, behind the head, is the saddle-shaped mantle, and under this are the genital opening and anus. On one side (almost always the right hand side) of the mantle is a respiratory opening, which is easy to see when open, but difficult to see when closed. This opening is known as the pneumostome. Within the mantle in some species is a very small, rather flat shell.
Like other snails, a slug moves by rhythmic waves of muscular contraction on the underside of its foot. It simultaneously secretes a layer of mucus on which it travels, which helps prevent damage to the foot tissues. Some slug species hibernate underground during the winter in temperate climates, but in other species, the adults die in the autumn. Around the foot is a 'foot fringe', which is made of small orange lines.
[edit]Vestigial shell
Most slugs retain a remnant of their shell, which is usually internalized. This organ generally serves as storage for calcium salts, often in conjunction with the digestive glands.[2]
An internal shell is present in the Limacidae[3] and Parmacellidae.[4]
Adult Philomycidae, [3] Onchidiidae[5] and Veronicellidae[6] lack shells.
[edit]Mucus
An active slug in Fremont, California
Slugs' bodies are made up mostly of water, and without a full-sized shell, their soft tissues are prone to desiccation. They must generate protective mucus to survive. Many species are most active just after rain because of the moist ground. In drier conditions, they hide in damp places such as under tree bark, fallen logs, rocks, and man-made structures, such as planters, to help retain body moisture.
Slugs produce two types of mucus: one which is thin and watery, and another which is thick and sticky. Both kinds of mucus are hygroscopic. The thin mucus spreads from the foot's centre to its edges, whereas the thick mucus spreads from front to back. Slugs also produce thick mucus which coats the whole body of the animal.
The mucus secreted by the foot contains fibres which help prevent the slug from slipping down vertical surfaces. The "slime trail" that a slug leaves behind has some secondary effects: other slugs coming across a slime trail can recognize the slime trail as produced by one of the same species, which is useful in finding a mate. Following a slime trail is also part of the hunting behavior of some carnivorous slugs.
Body mucus provides some protection against predators, as it can make the slug hard to pick up and hold by a bird's beak, for example, and the mucus itself can be distasteful.
Some species of slug secrete slime cords to lower themselves onto the ground, or to suspend a pair of slugs during copulation.
[edit]Reproduction
Close-up of mating great grey slugs
Slug eggs and baby
Slugs are hermaphrodites, having both female and male reproductive organs.
Once a slug has located a mate, they encircle each other and sperm is exchanged through their protruded genitalia. A few days later the slugs lay around 30 eggs in a hole in the ground, or beneath the cover of an object such as a fallen log.
Apophallation is a commonly seen practice among many slugs. In apophallating species, the penis curls like a corkscrew and during mating often becomes entangled in the mate's genitalia. Apophallation allows the slugs to separate themselves by one or both of the slugs chewing off the other's penis. Once its penis has been removed, the slug is still able to mate using only the female parts of its reproductive system.
[edit]Ecology
Arion vulgaris feeding on green leaves.
The recently discovered ghost slug hunts and eats earthworms
A. muscaria is prone to slug attack, as are many other fungi. It is unclear as to whether slugs are subject to the mushroom's drug effects.
An Arion ater slug eating an already dead earthworm.
Many slug species play an important ecosystem role by eating dead leaves, fungus, and decaying vegetable material. Other species eat parts of living plants.
Some slugs are predators and eat other slugs and snails, or earthworms.
Most carnivorous slugs on occasion also eat carrion, including dead of their own kind.
[edit]Predators
Frogs, toads, snakes, hedgehogs, Salamanders, eastern box turtles, rats, Caecilians and also some birds and beetles are slug predators.
Slugs, when attacked, can contract their body, making themselves harder and more compact, and combined with the slippery mucus is more difficult for many animals to grasp. The unpleasant taste of the mucus is also a deterrent.
Some slugs can self-amputate (autotomy) a portion of their tail to help the slug escape from a predator.[7]
[edit]Human relevance
The great majority of slug species are harmless to humans and to their interests, but a small number of species are serious pests of agriculture and horticulture. They can destroy foliage faster than plants can grow, thus killing even fairly large plants. They also feed on fruits and vegetables prior to harvest, making holes in the crop, which can make individual items unsuitable to sell for aesthetic reasons, and which can make the crop more vulnerable to rot and disease.
As control measures, baits are the norm in both agriculture and the garden. In recent years iron phosphate baits have emerged and are preferred over the toxic metaldehyde, especially because domestic or wild animals may be exposed to the bait. The environmentally safer iron phosphate has been shown to be at least as effective as poisonous baits.[8] Methiocarb baits are no longer widely used.
Other slug control methods are generally ineffective, but can be somewhat useful in small gardens. These include beer traps, [9] diatomaceous earth, crushed eggshells, coffee grounds, and copper.
It is of scientific interest that salt kills slugs by causing water to leave its body owing to osmosis [10] but this is not used for agricultural control as soil salinity is detrimental to crops.
In a few rare cases, humans have contracted parasite-induced meningitis from eating raw slugs.[11]
A banana slug, Ariolimax dolichophallus, named "Sammy" is the mascot of the University of California at Santa Cruz.[12]
In rural southern Italy, the garden slug Arion hortensis was used to treat gastritis, stomach ulcers or peptic ulcers by swallowing it whole and alive. Given that it is now known that most peptic ulcers are caused by Helicobacter pylori, the merit of swallowing a live slug is questionable. A clear mucus produced by the slug is also used to treat various skin conditions including dermatitis, warts, inflammations, calluses, acne and wounds.[13]
[edit]Taxonomy
Of the six orders of Pulmonata, two – the Onchidiacea and Soleolifera – solely comprise slugs. A third family, the Sigmurethra, contains various clades of snails, semi-slugs (i.e. snails whose shells are too small for them to retract fully into) and slugs.[1]
Subinfraorder Orthurethra
Superfamily Achatinelloidea Gulick, 1873
Superfamily Cochlicopoidea Pilsbry, 1900
Superfamily Partuloidea Pilsbry, 1900
Superfamily Pupilloidea Turton, 1831
Subinfraorder Sigmurethra
Superfamily Acavoidea Pilsbry, 1895
Superfamily Achatinoidea Swainson, 1840
Superfamily Aillyoidea Baker, 1960
Superfamily Arionoidea J.E. Gray in Turnton, 1840
Superfamily Athoracophoroidea
Family Athoracophoridae
Superfamily Orthalicoidea
Subfamily Bulimulinae
Superfamily Camaenoidea Pilsbry, 1895
Superfamily Clausilioidea Mörch, 1864
Superfamily Dyakioidea Gude & Woodward, 1921
Superfamily Gastrodontoidea Tryon, 1866
Superfamily Helicoidea Rafinesque, 1815
Superfamily Helixarionoidea Bourguignat, 1877
Superfamily Limacoidea Rafinesque, 1815
Superfamily Oleacinoidea H. & A. Adams, 1855
Superfamily Orthalicoidea Albers-Martens, 1860
Superfamily Plectopylidoidea Moellendorf, 1900
Superfamily Polygyroidea Pilsbry, 1894
Superfamily Punctoidea Morse, 1864
Superfamily Rhytidoidea Pilsbry, 1893
Family Rhytididae
Superfamily Sagdidoidera Pilsbry, 1895
Superfamily Staffordioidea Thiele, 1931
Superfamily Streptaxoidea J.E. Gray, 1806
Superfamily Strophocheiloidea Thiele, 1926
Superfamily Parmacelloidea
Superfamily Zonitoidea Mörch, 1864 |
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The Gastropoda or gastropods, more commonly known as snails and slugs, are a large taxonomic class within the phylum Mollusca. The class Gastropoda includes snails and slugs of all kinds and all sizes from microscopic to quite large. There are huge numbers of sea snails and sea slugs, as well as freshwater snails and freshwater limpets, and land snails and land slugs.
The class Gastropoda contains a vast total of named species, second only to the insects in overall number. The fossil history of this class goes all the way back to the Late Cambrian. There are 611 families of gastropods, of which 202 families are extinct, being found only in the fossil record.[3]
Gastropoda (previously known as univalves and sometimes spelled Gasteropoda) are a major part of the phylum Mollusca and are the most highly diversified class in the phylum, with 60, 000 to 80, 000[3][4] living snail and slug species. The anatomy, behavior, feeding and reproductive adaptations of gastropods vary significantly from one clade or group to another. Therefore, it is difficult to state many generalities for all gastropods.
The class Gastropoda has an extraordinary diversification of habitats. Representatives live in gardens, in woodland, in deserts, and on mountains; in small ditches, great rivers and lakes; in estuaries, mudflats, the rocky intertidal, the sandy subtidal, in the abyssal depths of the oceans including the hydrothermal vents, and numerous other ecological niches, including parasitic ones.
Although the name "snail" can be, and often is, applied to all the members of this class, commonly this word means only those species with an external shell large enough that the soft parts can withdraw completely into it. Those gastropods without a shell, and those with only a very reduced or internal shell, are usually known as slugs.
The marine shelled species of gastropod include edible species such as abalone, conches, periwinkles, whelks, and numerous other sea snails that produce seashells which are coiled in the adult stage, even though in some cases the coiling may not be very visible, for example in cowries. There are also a number of families of species such as all the various limpets, where the shell is coiled only in the larval stage, and is a simple conical structure after that.
Contents [hide]
1 Etymology
2 Diversity
3 Habitat
4 Anatomy
4.1 The shell
4.2 Body wall
4.3 Sensory organs and nervous system
4.4 Digestive system
4.5 Respiratory system
4.6 Circulatory system
4.7 Excretory system
4.8 Reproductive system
5 Life cycle
6 Feeding behavior
7 Genetics
8 Geological history
9 Taxonomy
10 References
11 External links
[edit]Etymology
The word "gastropod" is derived from the Ancient Greek words ?????? (gastér, stem: gastr-) "stomach", and ???? (poús, stem: pod-) "foot", hence stomach-foot. This is an anthropomorphic name, based on the fact that to humans it appears as if snails and slugs crawl on their bellies. In reality, snails and slugs have their stomach, the rest of their digestive system and all the rest of their viscera in a hump on the opposite, dorsal side of the body. In most gastropods this visceral hump is covered by, and contained within, the shell.
In the scientific literature, gastropods were described under the vernacular (French) name "gasteropodes" by Georges Cuvier in 1795.[2] The name was later Latinized.
The earlier name univalve means "one valve" or shell, in contrast to bivalve applied to mollusks such as clams and meaning that those animals possess two valves or shells.
[edit]Diversity
At all taxonomic levels, gastropods are second only to the insects in terms of their diversity.[5]
Gastropods are the class of molluscs which have the greatest numbers of named species. However estimates of the total number of gastropod species varies widely, depending on the cited sources. The number of gastropod species can be deduced from estimates of the number of described species of Mollusca with accepted names: about 85, 000[6] (minimum 50, 000, [6] maximum 120, 000[6]). But an estimate of the total number of Mollusca, including undescribed species, is about 240, 000 species.[7] The estimate of 85, 000 molluscs includes 24, 000 described species of terrestrial gastropods.[6]
Different estimates for aquatic gastropods (based on different sources) give about 30, 000 species[8] of marine gastropods, and about 5, 000 species of freshwater and brackish gastropods.[8] The total number of recent species of freshwater snails is about 4, 000.[9]
There are 444 recently extinct species of gastropods (extinct since the year 1500), [10] 18 species that are now extinct in the wild (but still existing in captivity)[10] and 69 "possibly extinct" species.[10]
The number of prehistoric (fossil) species of gastropods is at least 15, 000 species.[11]
[edit]Habitat
Main articles: sea snail, sea slug, Terrestrial animal#Gastropods, land snail, semi-slug, and slug
Some of the more familiar and better-known gastropods are terrestrial gastropods (the land snails and slugs) and some live in freshwater, but more than two thirds of all named species live in a marine environment.
Gastropods have a worldwide distribution from the near Arctic and Antarctic zones to the tropics. They have become adapted to almost every kind of existence on earth, having colonized every medium available except the air.
In habitats where there is not enough calcium carbonate to build a really solid shell, such as on some acidic soils on land, there are still various species of slugs, and also some snails with a thin translucent shell, mostly or entirely composed of the protein conchiolin.
Snails such as Sphincterochila boissieri and Xerocrassa seetzeni have adapted to desert conditions, other snails have adapted to an existence in ditches, near deepwater hydrothermal vents, the pounding surf of rocky shores, caves, and many other diverse areas.
[edit]Anatomy
The anatomy of a common air-breathing land snail such as Helix aspersa. Note that much of this anatomy does not apply to gastropods in other clades or groups.
The anatomy of an aquatic snail with a gill, a male prosobranch gastropod. Note that much of this anatomy does not apply to gastropods in other clades.
Light yellow - body
Brown - shell and operculum
Green - digestive system
Light purple - gills
Yellow - osphradium
Red - heart
Pink -
Dark violet -
1. foot
2. cerebral ganglion
3. pneumostome
4. upper commissura
5. osphradium
6. gills
7. pleural ganglion
8. atrium of heart
9. visceral ganglion
10. ventricle
11. foot
12. operculum
13. brain
14. mouth
15. tentacle (chemosensory, 2 or 4)
16. eye
17. penis (everted, normally internal)
18. esophageal nerve ring
19. pedal ganglion
20. lower commissura
21. vas deferens
22. pallial cavity / mantle cavity / respiratory cavity
23. parietal ganglion
24. anus
25. hepatopancreas
26. gonad
27. rectum
28. nephridium
Snails are distinguished by an anatomical process known as torsion, where the visceral mass of the animal rotates 180° to one side during development, such that the anus is situated more or less above the head. This process is unrelated to the coiling of the shell, which is a separate phenomenon. Torsion is present in all gastropods, but the opisthobranch gastropods are secondarily de-torted to various degrees.[12][13]
Torsion occurs in two mechanistic stages. The first is muscular and the second is mutagenetic. The effects of torsion are primarily physiological - the organism develops an asymmetrical nature with the majority of growth occurring on the left side. This leads to the loss of right-paired appendages (e.g. ctenidia (comb-like respiratory apparatus), gonads, nephridia, etc.). Furthermore, the anus becomes redirected to the same space as the head. This is speculated to have some evolutionary function, as prior to torsion, when retracting into the shell, first the posterior end would get pulled in, and then the anterior. Now, the front can be retracted more easily, perhaps suggesting a defensive purpose.
However, this "rotation hypothesis" is being challenged by the "asymmetry hypothesis" in which the gastropod mantle cavity originated from one side only of a bilateral set of mantle cavities.[14]
Gastropods typically have a well-defined head with two or four sensory tentacles with eyes, and a ventral foot, which gives them their name (Greek gaster, stomach, and poda, feet). The foremost division of the foot is called the propodium. Its function is to push away sediment as the snail crawls. The larval shell of a gastropod is called a protoconch.
[edit]The shell
Main article: Gastropod shell
The shell of Zonitoides nitidus, a small land snail, has dextral coiling, which is typical (but not universal) in gastropod shells.
Upper image: dorsal view of the shell, showing the apex
Central image: lateral view showing the spire and aperture of the shell
Lower image: basal view showing the umbilicus
Most shelled gastropods have a one piece shell, typically coiled or spiraled. This coiled shell usually opens on the right-hand side (as viewed with the shell apex pointing upward). Numerous species have an operculum, which in many species acts as a trapdoor to close the shell. This is usually made of a horn-like material, but in some molluscs it is calcareous. In the land slugs, the shell is reduced or absent, and the body is streamlined.
[edit]Body wall
Some sea slugs are very brightly colored. This serves either as a warning, when they are poisonous or contain stinging cells, or to camouflage them on the brightly-colored hydroids, sponges and seaweeds on which many of the species are found.
Lateral outgrowths on the body of nudibranchs are called cerata. These contain a part of digestive gland, which is called the diverticula.
[edit]Sensory organs and nervous system
The upper pair of tentacles on the head of Helix pomatia have eye spots, but the main sensory organs of the snail are sensory receptors for olfaction, situated in the epithelium of the tentacles.
Main articles: Sensory organs of gastropods and Nervous system of gastropods
Sensory organs of gastropods include olfactory organs, eyes, statocysts and mechanoreceptors.[15] Gastropods have no hearing.[15]
In terrestrial gastropods (land snails and slugs), the olfactory organs, located on the tips of the 4 tentacles, are the most important sensory organ, [15] The chemosensory organs of opisthobranch marine gastropods are called rhinophores.
The majority of gastropods have simple visual organs, eye spots, that are situated either at the tip of the tentacles or the base of the tentacles. However "eyes" in gastropods range from these simple ocelli which cannot process an image being only able to distinguish light and dark, to more complex pit eyes, and even to lens eyes.[16] In land snails and slugs, vision is not the most important sense, because they are mainly nocturnal animals.[15]
The nervous system of gastropods includes the peripheral nervous system and the central nervous system. The central nervous system consist of ganglia connected by nerve cells. It includes paired ganglia: the cerebral ganglia, pedal ganglia, osphradial ganglia, pleural ganglia, parietal ganglia and the visceral ganglia. There are sometimes also buccal ganglia.[15]
[edit]Digestive system
Main articles: Digestive system of gastropods and Radula
The radula of a gastropod is usually adapted to the food that a species eats. The simplest gastropods are the limpets and abalones, herbivores that use their hard radula to rasp at seaweeds on rocks.
Many marine gastropods are burrowers, and have a siphon that extends out from the mantle edge. Sometimes the shell has a siphonal canal to accommodate this structure. A siphon enables the animal to draw water into their mantle cavity and over the gill. They use the siphon primarily to "taste" the water to detect prey from a distance. Gastropods with siphons tend to be either predators or scavengers.
[edit]Respiratory system
Main articles: Respiratory system of gastropods and Respiratory system#Anatomy of respiratory system in invertebrates
Almost all marine gastropods breathe with a gill, but many freshwater species, and the majority of terrestrial species, have a pallial lung. Gastropods with a lung belong to one group with common descent, the Pulmonata, however, gastropods with gills are paraphyletic. The respiratory protein in almost all gastropods is hemocyanin, but a pulmonate family Planorbidae have hemoglobin as respiratory protein.
In one large group of sea slugs, the gills are arranged as a rosette of feathery plumes on their backs, which gives rise to their other name, nudibranchs. Some nudibranchs have smooth or warty backs and have no visible gill mechanism, such that respiration may likely take place directly through the skin.
[edit]Circulatory system
Main article: Circulatory system of gastropods
Gastropods have open circulatory system and the transport fluid is hemolymph. Hemocyanin is present in the hemolymph as the respiratory pigment.
[edit]Excretory system
Main article: Excretory system of gastropods
The primary organs of excretion in gastropods are nephridia, which produce either ammonia or uric acid as a waste product. The nephridium also plays an important role in maintaining water balance in freshwater and terrestrial species. Additional organs of excretion, at least in some species, include pericardial glands in the body cavity, and digestive glands opening into the stomach.
[edit]Reproductive system
Main article: Reproductive system of gastropods
Courtship is a part of mating behavior in some gastropods including some of the Helicidae. Again, in some land snails, an unusual feature of the reproductive system of gastropods is the presence and utilization of love darts.
In many marine gastropods other than the opisthobranchs, there are separate sexes; most land gastropods however are hermaphrodites.
[edit]Life cycle
A 9-hour-old trochophore of Haliotis asinina
sf - shell field
mating behaviour of Elysia timida
The main aspects of the life cycle of gastropods include:
Egg laying and the eggs of gastropods
The Embryonic development of gastropods
The larvae or larval stadium: some gastropods may be trochophore and/or veliger
Estivation and hibernation (each of these are present in some gastropods only)
The growth of gastropods
Courtship of gastropods and mating of gastropods: fertilisation is internal or external according to the species. External fertilisation is common in marine gastropods.
[edit]Feeding behavior
Marine gastropods include some that are herbivores, detritus feeders, predatory carnivores, scavengers, parasites, and also a few ciliary feeders, in which the radula is reduced or absent. Land-dwelling species can chew up leaves, bark, fruit and decomposing animals while marine species can scrape algae off the rocks on the sea floor. In some species that have evolved into endoparasites, such as Parenteroxenos doglieli, many of the standard gastropod features are strongly reduced or absent.
A few sea slugs are herbivores and some are carnivores. Many have distinct dietary preferences and regularly occur in close association with their food species.
Some predatory carnivorous gastropods include, for example: Cone shells, Testacella, Daudebardia, Ghost slug and others.
[edit]Genetics
Gastropods exhibit an important degree of variation in mitochondrial gene organization when compared to other animals.[17] Main events of gene rearrangement occurred at the origin of Patellogastropoda and Heterobranchia, whereas fewer changes occurred between the ancestors of Vetigastropoda (only tRNAs D, C and N) and Caenogastropoda (a large single inversion, and translocations of the tRNAs D and N).[17] Within Heterobranchia, gene order seems to be relatively conserved and gene rearrangements are mostly related with transposition of tRNA genes.[17]
[edit]Geological history
Fossil gastropod and attached mytilid bivalves on a Jurassic limestone bedding plane of the Matmor Formation in southern Israel.
Helix aspersa: a European pulmonate land snail that has been accidentally introduced in many countries throughout the world.
See also: :fr:Gastropoda (classification phylogénétique) and List of marine gastropod genera in the fossil record
The first gastropods were exclusively marine, with the earliest representatives of the group appearing in the Late Cambrian (Chippewaella, Strepsodiscus). Early Cambrian forms like Helcionella and Scenella are no longer considered gastropods, and the tiny coiled Aldanella of earliest Cambrian time is probably not even a mollusk. By the Ordovician period the gastropods were a varied group present in a range of aquatic habitats. Commonly, fossil gastropods from the rocks of the early Palaeozoic era are too poorly preserved for accurate identification. Still, the Silurian genus Poleumita contains fiftean identified species. Fossil gastropods were less common during the Palaeozoic era than bivalves.
Most of the gastropods of the Palaeozoic era belong to primitive groups, a few of which still survive today. By the Carboniferous period many of the shapes we see in living gastropods can be matched in the fossil record, but despite these similarities in appearance the majority of these older forms are not directly related to living forms. It was during the Mesozoic era that the ancestors of many of the living gastropods evolved.
One of the earliest known terrestrial (land-dwelling) gastropods is Maturipupa, which is found in the Coal Measures of the Carboniferous period in Europe, but relatives of the modern land snails are rare before the Cretaceous period, when the familiar Helix first appeared.
Cepaea nemoralis: another European pulmonate land snail, which has been introduced to many other countries
In rocks of the Mesozoic era, gastropods are slightly more common as fossils, their shells are often well preserved. Their fossils occur in ancient beds deposited in both freshwater and marine environments. The "Purbeck Marble" of the Jurassic period and the "Sussex Marble" of the early Cretaceous period, which both occur in southern England, are limestones containing the tightly packed remains of the pond snail Viviparus.
Rocks of the Cenozoic era yield very large numbers of gastropod fossils, many of these fossils being closely related to modern living forms. The diversity of the gastropods increased markedly at the beginning of this era, along with that of the bivalves.
Certain trail-like markings preserved in ancient sedimentary rocks are thought to have been made by gastropods crawling over the soft mud and sand. Although these trails are of debatable origin, some of them do resemble the trails made by living gastropods today.
Gastropod fossils may sometimes be confused with ammonites or other shelled cephalopods. An example of this is Bellerophon from the limestones of the Carboniferous period in Europe, the shell of which is planispirally coiled and can be mistaken for the shell of a cephalopod.
Gastropods are one of the groups that record the changes in fauna caused by the advance and retreat of the Ice Sheets during the Pleistocene epoch.
[edit]Taxonomy
A group of fossil shells of Turritella cingulifera from the Pliocene of Cyprus.
Five different views of a shell of a Fulguropsis species
Since Darwin, biological taxonomy has tried to reflect the presumed phylogeny of organisms, i.e. the tree of life. The classifications used in taxonomy attempt to represent the precise interrelatedness of the various species. The taxonomy of the Gastropoda as shown in various texts can differ in major ways.
In the older classification of the gastropods, there were four subclasses:[18]
Opisthobranchia (gills to the right and behind the heart).
Gymnomorpha (no shell)
Prosobranchia (gills in front of the heart).
Pulmonata (with a lung instead of gills)
Main article: Taxonomy of the Gastropoda (Ponder & Lindberg, 1997)
The taxonomy of the Gastropoda is under constant revision, and more and more of the old taxonomy is being abandoned, as the results of DNA studies slowly become clearer. Nevertheless a few of the older terms such as "opisthobranch" and "prosobranch" are still sometimes used in a descriptive way.
New insights based on DNA sequencing of gastropods have produced some revolutionary new taxonomic insights. In the case of the Gastropoda, the taxonomy is now gradually being rewritten to embody strictly monophyletic groups (only one lineage of gastropods in each group). Integrating new findings into a working taxonomy will continue to be a challenge in coming years. Consistent ranks within the taxonomy at the level of subclass, superorder, order and suborder have already been abandoned as unworkable. Ongoing revisions of the higher taxonomic levels are to be expected in the near future.
Convergent evolution, which appears to exist at especially high frequency in the class Gastropoda class, may account for the observed differences between the older phylogenies which were based on morphological data, and more recent gene-sequencing studies.
Main articles: Taxonomy of the Gastropoda (Bouchet & Rocroi, 2005) and Changes in the taxonomy of gastropods since 2005
Bouchet & Rocroi (2005)[3][19] made sweeping changes in the systematics, resulting in a taxonomy that is a step closer to the evolutionary history of the phylum.
The Bouchet & Rocroi classification system is based partly on the older systems of classification, and partly on new cladistic research. In the past, the taxonomy of gastropods was largely based on phenetic morphological characters of the taxa. The recent advances are more based on molecular characters from DNA[20] and RNA research. This has made the taxonomical ranks and their hierarchy controversial. The debate about these issues is not likely to end soon.
In the Bouchet, Rocroi et al. taxonomy, the authors have used unranked clades for taxa above the rank of superfamily (replacing the ranks suborder, order, superorder and subclass), while using the traditional Linnaean approach for all taxa below the rank of superfamily. Whenever monophyly has not been tested, or is known to be paraphyletic or polyphyletic, the term "group" or "informal group" has been used. The classification of families into subfamilies is often not well resolved, and should be regarded as the best possible hypothesis.
In 2004, Brian Simison and David R. Lindberg showed possible diphyletic origins of the Gastropoda based on mitochondrial gene order and amino acid sequence analyses of complete genes.[21] |
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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.
Contents [hide]
1 Biology
1.1 Physical characteristics
1.2 Internal anatomy
1.3 Growth of the shell
1.4 Hibernation and estivation
1.5 Reproduction
1.6 Lifespan
1.7 Diet
1.8 Predators
2 Snails as human food
2.1 Europe
2.2 Africa
3 See also
4 References
5 External links
[edit]Biology
[edit]Physical characteristics
Land snails in Negev desert in Israel.
Underside of a snail climbing a blade of grass, showing the muscular foot and the pneumostome or respiratory pore on the animal's right side
Land snails move by gliding along on their muscular foot, which is lubricated with mucus and covered with epithelial cilia.[1] 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[2]). 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.[3] 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.
Snail with a rightwardly spiraling shell.
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.[4][5]
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.
[edit]Internal anatomy
The anatomy of a common snail
Garden Snail, Helix aspersa defecating
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.[6]
[edit]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.
Sinistral (left-handed) species of snail from western India
[edit]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.
[edit]Reproduction
Two Helicid snails make contact prior to mating.
Two Helix aspersa Garden snails mating
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 [7] to 5 years.[8] Adverse environmental conditions may delay the onset of sexual maturity in some snails.[9]
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.[citation needed] Irrespective of their rate of growth, however, it will still take at least 1 year before they are sexually mature.[10]
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.[11][12]
[edit]Lifespan
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.[13]
[edit]Diet
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.
[edit]Predators
The larva of a firefly (Lampyris noctiluca) attacking and eating a land snail
Land snails have many natural predators, including members of all the land vertebrate groups, examples being thrushes and hedgehogs, also invertebrates including decollate snails, ground beetles, leeches, and even the predatory caterpillar Hyposmocoma molluscivora.
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, the final host of the worm.
Humans also pose great dangers to snails in the wild. Pollution and habitat destruction have caused the extinction of a number of snail species in recent years.[14][15] To protect themselves against predators, land snails retract their soft parts into their shell when resting; some bury themselves.
[edit]Snails as human food
This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (March 2009)
A snail farm in Provence
Snails have been eaten for thousands of years, going back at least as far as the Pleistocene. Archaeological evidence of snail consumption is especially abundant in Capsian sites in North Africa, but is also found throughout the Mediterranean region in archaeological sites dating between 12, 000 and 6, 000 years ago.[16][17] However, wild-caught land snails which are prepared for the table but are undercooked can harbor a parasite (Angiostrongylus cantonensis) that may cause a rare kind of meningitis.[18]
Snail eggs, sold as snail caviar, are a specialty food that is growing in popularity in European cuisine.[19]
[edit]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, 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; known as l'Escargot de Bourgogne).
Helix aspersa:
Helix 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 Atlantic coast; Helix aspersa aspersa known as le Petit-gris).
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 escargots. 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.
Portuguese caracóis snack, species probably Otala lactea.
Snails are also popular in Portuguese cuisine where they are called in 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.[20]
Cooked French escargots, species Helix pomatia
Cooked Spanish "caracoles a la madrileña", species Helix aspersa
Traditional Spanish cuisine also uses snails ("caracoles" in Spanish; "caragols" or "cargols" in Catalan), consuming several species such as Helix aspersa, Otala lactea, Otala punctata or Theba pisana among others. Snails are very popular in Andalusia, Valencia and specially Catalonia. There are even snails celebration, as the "Aplec del cargol", which takes place in Lleida each May and draws more than 200, 000 visitors from abroad. Small to medium-size varieties are usually cooked in several spicy sauces or even in soups and eaten as appetizer. The bigger ones may be reserved for other more elaborated dishes, such as the "arroz con conejo y caracoles" (a paella-style rice with snails and rabbit meat, from the inner regions of south-eastern Spain), "cabrillas" (snails in spicy tomato sauce, typical from western Andalusia) or the Catalonian caragols à la llauna (grilled inside their own shells and then eaten after dipping them in garlic mayonnaise) and à 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 squashes. Limpets and sea snails also find their way to the Greek table around the country. Another snail cooking method is the Kohli Bourbouristi (??????? ????(?)??????????)[21] a traditional Cretan dish, which consists of fried snails in olive oil with salt, vinegar and rosemary.
They feature often in Cyprus taverna menus, under the mezes.[22]
In Sicily, snails (or babbaluci as they are commonly called in 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.
Snails (or bebbux as they are called in Maltese) are a dish on the Mediterranean island of Malta, generally prepared and served in the Sicilian manner.
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. Some species such as the Roman Snail are protected in the wild in several European countries and must not be collected, but the Roman Snail and the Garden Snail (Cornu aspersum) are cultivated on snail farms.[13]
Although there is not usually considered to be a tradition of snail eating in Britain, common garden snails Helix aspersa were eaten in the Southwick area of Sunderland in North East England. They were collected from quarries and along the stone walls of railway embankments during the winter when the snails were hibernating and had voided the contents of their guts. Gibson writes that this tradition was introduced in the 19th century by French immigrant glass workers.[23] "Snail suppers" were a feature of local pubs and Southwick working men were collecting and eating snails as late as the 1970s, though the tradition may now have died out.
[edit]Africa
Achatina fulica, the giant east African snail, is canned and sliced and sold to consumers as escargot.[citation needed]
In parts of West Africa, specifically Ghana, snails are served as a delicacy. [1] Achatina achatina, Ghana tiger snails, are also known as some of the largest snails in the world.
In North Morocco, small snails are eaten as snacks in spicy soup. The recipe is identical to this prepared in Andalusia (South Spain), showing the close cultural relationship between both kinds of cuisine.
[edit]See also
Freshwater snail
Sea slug
Sea snail
Slug
Cretan diet |
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A freshwater snail is one kind of freshwater mollusc, the other kind being freshwater clams and mussels, i.e. freshwater bivalves. Specifically a freshwater snail is a gastropod that lives in a watery non-marine (freshwater) habitat. The majority of freshwater gastropods have a shell, with very few exceptions. Some groups of snails that live in freshwater respire using gills. Others need to surface to breathe air.
According to present classification efforts, there are about 4, 000 species of freshwater gastropods (3, 795-3, 972).[1]
There exist at least 33-38 independent lineages of gastropods, that have successfully invaded freshwater environment.[2] There is not possible to identify the exact number of these lineages yet, because it have to be clarified within Cerithioidea.[2] From six to eight of these independent lineages occur in the North America.[3]
Contents [hide]
1 Taxonomy
1.1 2005 taxonomy
1.2 2010 taxonomy
2 Neritimorpha
3 Caenogastropoda
4 Heterobranchia
5 As human food
6 Aquarium snails
7 Parasitology
8 See also
9 References
10 Further reading
[edit]Taxonomy
[edit]2005 taxonomy
The following cladogram is an overview of the main clades of gastropods based on the taxonomy of Bouchet & Rocroi (2005), [4] with families that contain freshwater species marked in boldface:[1] (Some of these highlighted families consist entirely of freshwater species, but some of them also contain, or even mainly consist of, marine species.)
† Paleozoic molluscs of uncertain systematic position
† Basal taxa that are certainly Gastropoda
Patellogastropoda
Vetigastropoda
Cocculiniformia
Neritimorpha
† Paleozoic Neritimorpha of uncertain systematic position
† Cyrtoneritimorpha
Cycloneritimorpha: Neritiliidae and Neritidae
Caenogastropoda
Caenogastropoda of uncertain systematic position
Architaenioglossa: Ampullariidae and Viviparidae
Sorbeoconcha: Melanopsidae, Pachychilidae, Paludomidae, Pleuroceridae, Semisulcospiridae and Thiaridae
Hypsogastropoda
Littorinimorpha: Littorinidae, Amnicolidae, Assimineidae, Bithyniidae, Cochliopidae, Helicostoidae, Hydrobiidae, Lithoglyphidae, Moitessieriidae, Pomatiopsidae and Stenothyridae
Ptenoglossa
Neogastropoda: Buccinidae and Marginellidae
Heterobranchia
Lower Heterobranchia: Glacidorbidae and Valvatidae
Opisthobranchia
Cephalaspidea
Thecosomata
Gymnosomata
Aplysiomorpha
Acochlidiacea: Acochlidiidae, Tantulidae and Strubelliidae
Sacoglossa
Cylindrobullida
Umbraculida
Nudipleura
Pulmonata
Basommatophora: Chilinidae, Latiidae, Acroloxidae, Lymnaeidae. Planorbidae ? and Physidae - all these six families together form the clade Hygrophila
Eupulmonata
[edit]2010 taxonomy
The following cladogram is an overview of the main clades of gastropods based on the taxonomy of Bouchet & Rocroi (2005), [4] modified after Jörger et al. (2010)[5] and simplified with families that contain freshwater species marked in boldface:[1] (Marine gastropods (Siphonarioidea, Sacoglossa, Amphiboloidea, Pyramidelloidea) are not depicted within Panpulmonata for simplification. Some of these highlighted families consist entirely of freshwater species, but some of them also contain, or even mainly consist of, marine species.)
† Paleozoic molluscs of uncertain systematic position
† Basal taxa that are certainly Gastropoda
Patellogastropoda
Vetigastropoda
Cocculiniformia
Neritimorpha
† Paleozoic Neritimorpha of uncertain systematic position
† Cyrtoneritimorpha
Cycloneritimorpha: Neritiliidae and Neritidae
Caenogastropoda
Caenogastropoda of uncertain systematic position
Architaenioglossa: Ampullariidae and Viviparidae
Sorbeoconcha: Melanopsidae, Pachychilidae, Paludomidae, Pleuroceridae, Semisulcospiridae and Thiaridae
Hypsogastropoda
Littorinimorpha: Littorinidae, Amnicolidae, Assimineidae, Bithyniidae, Cochliopidae, Helicostoidae, Hydrobiidae, Lithoglyphidae, Moitessieriidae, Pomatiopsidae and Stenothyridae
Ptenoglossa
Neogastropoda: Buccinidae and Marginellidae
Heterobranchia
Lower Heterobranchia: Valvatidae
Euthyneura
Nudipleura
Euopisthobranchia
Panpulmonata
Glacidorboidea with the only family Glacidorbidae
Hygrophila: Chilinidae, Latiidae, Acroloxidae, Lymnaeidae. Planorbidae ? and Physidae
Acochlidiacea: Acochlidiidae, Tantulidae and Strubelliidae
Eupulmonata
[edit]Neritimorpha
Primitive "Prosobranch" gilled snails with a shelly operculum.
Neritiliidae, 5 extant freshwater species[1]
Neritidae, largely confined to the tropics, also the rivers of Europe, family includes the marine "nerites".[6] There are about 110 extant freshwater species.[1]
Family Neritidae, shells of Theodoxus fluviatilis.
Family Neritidae, Neritina natalensis
[edit]Caenogastropoda
A large group of gilled operculate snails, largely marine. In freshwater habitats there are ten major families, as well as other families of lesser importance:
Architaenioglossa
Ampullariidae, an exclusively freshwater family that is largely tropical and includes the large "apple snails" kept in aquaria.[6] 105-170 species.[1]
Viviparidae, medium to large snails, live-bearing, commonly referred to as "mystery snails". World wide except South America, and everywhere confined to fresh waters.[6] 125-150 species.[1]
Family Ampullariidae, Pomacea bridgesii.
Family Viviparidae, Viviparus viviparus.
Sorbeoconcha
Melanopsidae, family native to rivers draining to the Mediterranean, also Middle East, and some South Pacific islands.[6] About 25-50 species.[1]
Pachychilidae - 165-225 species.[1] native to South and Central America. Formerly included with the Pleuroceridae by many authors.
Paludomidae - about 100 species in south Asia, diverse in African Lakes, and Sri Lanka.[1] Formerly classified with the Pleuroceridae by some authors.
Pleuroceridae, abundant and diverse in eastern North America, largely high-spired snails of small to large size.[6] About 150 species.[2]
Semisulcospiridae, - primarily eastern Asia, Japan, also the Juga snails of northwestern North America. Formerly included with the Pleuroceridae. About 50 species.[2]
Thiaridae, high-spired parthenogenic snails of the tropics, includes those referred to as "trumpet snails" in aquaria.[6] About 110 species.[2]
Family Pleuroceridae, Io fluvialis.
Family Semisulcospiridae, Semisulcospira kurodai.
Family Thiaridae, Melanoides tuberculata.
Littorinimorpha
Littorinidae - 2 species in the genus Cremnoconchus are freshwater living in waterfalls.[1] Other species are marine.
Amnicolidae - about 200 species.[1]
Assimineidae - about 20 freshwater species, [1] other are marine
Bithyniidae, small snails, native to Eastern Hemisphere.[6] About 130 species.[1]
Cochliopidae - 246 species.[1]
Helicostoidae, the only species Helicostoa sinensis lives in China.[1]
Hydrobiidae, small to very small snails found world wide.[6] About 1250 freshwater species[1] other are marine.
Clea helena, family Buccinidae.
Lithoglyphidae - about 100 species.[1]
Moitessieriidae - 55 species.[1]
Pomatiopsidae, small amphibious snails scattered worldwide, most diverse in eastern and Southeast Asia.[6] About 170 species.[1]
Stenothyridae - about 60 freshwater species, [1] others are marine.
Neogastropoda
Buccinidae - 8-10 freshwater species in the genus Clea, [1] native to Southeast Asia. Other Buccinidae are marine.
Marginellidae - 2 freshwater species in the genus Rivomarginella, [1] native to Southeast Asia. Other Marginellidae are marine.
[edit]Heterobranchia
Family Valvatidae, shells of Valvata sibirica, scale is in mm
Acochlidium fijiiensis is one of very few freshwater gastropods without a shell.
Lower Heterobranchia
Glacidorbidae - 20 species.[1]
Valvatidae, small low-spired snails referred to as "valve snails". 71 species.[1]
Acochlidiacea
Acochlidiidae (including synonym Strubelliidae) - 5 shell-less species:[1] Acochlidium amboinense, Acochlidium bayerfehlmanni, Acochlidium fijiiensis, Palliohedyle sutteri and Strubellia paradoxa[7]
Tantulidae - there is only one species[1] which is shell-less Tantulum elegans.
Pulmonata, Basommatophora
Basommatophorans are pulmonate or air-breathing aquatic snails, characterized by having their eyes located at the base of their tentacles, rather than at the tips, as in the true land snails Stylommatophora. The majority of basommatophorans have shells that are thin, translucent, and relatively colorless, and all five freshwater basommatophoran families lack an operculum.
Chilinidae, small to medium-sized snails confined to temperate and cold South America.[6] About 15 species.[1]
Latiidae, small limpet-like snails confined to New Zealand.[6] One[1] or three species.
Acroloxidae - about 40 species.[1]
Lymnaeidae, found worldwide, but are most numerous in temperate and northern regions.[6] These are the dextral (right-handed) pond snails. About 100 species.
Planorbidae, "rams horn" snails, with a worldwide distribution.[6] About 250 species.[1]
Physidae, left-handed (sinistral) "pouch snails", native to Europe, Asia, North America.[6] About 80 species.[1]
Family Lymnaeidae, Lymnaea stagnalis.
Family Physidae, Physella acuta.
Family Planorbidae, Planorbarius corneus.
[edit]As human food
Several different freshwater snail species are eaten in Asian cuisine.
Archaeological investigations in Guatemala have revealed that the diet of the Maya of the Classic Period (AD 250-900) included freshwater snails.[8]
A dish of cooked freshwater nerites from the Rajang River, Sarawak, Malaysia
A dish of cooked freshwater snails, ampullariids and viviparids from Poipet, Cambodia
[edit]Aquarium snails
In the developed world, people encounter freshwater snails most commonly in aquaria along with tropical fish. Species available vary in different parts of the world. In the United States, commonly available species include ramshorn snails such as Planorbella duryi, apple snails such as Pomacea bridgesii and the high-spired thiarid malaysian trumpet snail Melanoides tuberculata.
[edit]Parasitology
Life cycle of two liver fluke species which have freshwater snails as intermediate hosts
Freshwater snails are widely known to be hosts in the lifecycles of a variety of human and animal parasites, particularly trematodes or "flukes". Some of these relations for prosobranch snails include Oncomelania in the family Pomatiopsidae as hosts of Schistosoma, and Bithynia, Parafossarulus and Amnicola as hosts of Opisthorchis.[9] Thiara and Semisulcospira may host Paragonimus, and Goniobasis (older term including Elimia, Juga and other small high-spired pleurocerid snails) may host Nanophyetus salmincola.[9] Basommatophoran snails are even more widely infected, with many Biomphalaria (Planorbidae) serving as hosts for Schistosoma mansoni, Fasciolopsis and other parasitic groups.[9] The tiny Bulinus snails are hosts for Schistosoma haematobium.[9] Lymnaeid snails (Lymnaeidae) serve as hosts for Fasciola and the cerceriae causing swimmer's itch.[9]
[edit]See also
Land snail
Sea slug
Sea snail
Slug |
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Sea slug is a common name used for several different groups of saltwater snails that either lack a shell or have only an internal shell, in other words this name is used for various lineages of marine gastropod mollusks that are either not conchiferous (shell-bearing) or appear not to be.
The phrase "sea slug" is often applied to nudibranchs, members of the order Nudibranchia within the opisthobranch gastropods. Many nudibranchs are colorful and are a noticeable part of the underwater fauna. However the phrase "sea slug" is also applied to various other groups within the Opisthobranchia including the sea hares, the sacoglossans, various families of bubble snails (Cephalaspidea) and others, some of which have reduced shells, and many of which are shell-less.
Other groups of shell-less or reduced-shell marine gastropods which are sometimes called sea slugs include the sorbeoconch family Pterotracheoidea and the pulmonate (air-breathing) sea slug family Onchidiidae.
[edit]See also
Freshwater snail
Land snail
Sea snail
Slug |
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Sea snail is a common name for those snails that normally live in saltwater, marine gastropod molluscs. (The taxonomic class Gastropoda also includes snails that live in other habitats, i.e. land snails and freshwater snails.)
Sea snails are marine gastropods that have shells. Those marine gastropods that have no shells, or have only internal shells, are variously known by other common names, including sea slug, sea hare, nudibranch, etc.
Many sea snails are edible and are exploited as food sources by humans. Some well-known kinds of edible sea snails are abalone, conch, limpets, whelks (such as the North American Busycon species and the North Atlantic Buccinum undatum) and periwinkles including Littorina littorea.
There is enormous diversity within sea snails; many very different clades of gastropods are either dominated by, or consist exclusively of, sea snails. Because of this great variability, it is not possible to generalize about the feeding, reproduction, habitat and so on of sea snails. Instead it is necessary to look at the articles about individual clades, families, genera or species.
Contents [hide]
1 Shells
2 Anatomy
3 Human uses
4 Use by other animals
5 Definition
6 Taxonomy
6.1 2005 taxonomy
7 Cultural references
8 See also
9 References
[edit]Shells
A group of Patella vulgata limpets on a rock in Pembrokeshire
The shell of Syrinx aruanus can be up to 91 cm long
The shells of most species of sea snails are spirally coiled; some however have shells that are conical, and these are often referred to by the common name of limpets.
In one unusual family Juliidae, the shell of the snail has become two hinged plates closely resembling those of a bivalve; this family is sometimes called the "bivalved gastropods".
The shells of living species of sea snails range in size from Syrinx aruanus, the largest living shelled gastropod species, to minute species whose shells are under 1 mm at adult size.
Because in many cases the shells of sea snails are strong and durable, as a group they are well represented in the fossil record.
[edit]Anatomy
Sea snails are a very large group of animals and a very diverse one. Most snails that live in saltwater respire using a gill or gills, a few species however have a lung, are intertidal, and are active only at low tide when they can move around in the air. These air-breathing species include false limpets in the family Siphonariidae and another group of false limpets in the family Trimusculidae.
Many (but not all) sea snails have an operculum.
[edit]Human uses
A number of species of edible whelks for sale at a fish market in Japan
A number of species of sea snails are exploited by humans for food, including abalone, conch, limpets, whelks (such as the North American Busycon species and the North Atlantic Buccinum undatum) and periwinkles including Littorina littorea.
The shells of sea snails are often found by humans as one kind of seashell that washes up on beaches. Because the shells of many sea snails are attractive and durable, they have been used by humans to make necklaces and other jewelry from prehistoric times to the current day.
The shells of a few species of large sea snails within the Vetigastropoda have a thick layer of nacre and have been exploited as a source of mother of pearl. Historically the button industry relied on these species for a number of years.
[edit]Use by other animals
A hermit crab which is occupying a shell of Acanthina punctulata has been disturbed, and has retracted into the shell, using its claws to bar the entrance in the same way that the snail used its operculum.
The shells of sea snails are used for protection by many kinds of hermit crabs. A hermit crab carries the shell by grasping the central columella of the shell using claspers on the tip of its abdomen.
[edit]Definition
It is not always easy to decide whether some gastropods should be called sea snails. Some species that live in brackish water (such as certain neritids) can be listed as either freshwater snails or marine snails, and some species that live right at, or right above, the high tide level (for example species in the genus Truncatella), are sometimes considered to be sea snails and sometimes listed as land snails.
[edit]Taxonomy
[edit]2005 taxonomy
The following cladogram is an overview of the main clades of living gastropods based on the taxonomy of Bouchet & Rocroi (2005), [1] with taxa that contain saltwater or brackish water species marked in boldface (some of the highlighted taxa consist entirely of marine species, but some of them also contain freshwater or land species.)
Clade Patellogastropoda
Clade Vetigastropoda
Clade Cocculiniformia
Clade Neritimorpha
Clade Cycloneritimorpha
Clade Caenogastropoda
Informal group Architaenioglossa
Clade Sorbeoconcha
Clade Hypsogastropoda
Clade Littorinimorpha
Informal group Ptenoglossa
Clade Neogastropoda
Clade Heterobranchia
Informal group Lower Heterobranchia
Informal group Opisthobranchia
Clade Cephalaspidea
Clade Thecosomata
Clade Gymnosomata
Clade Aplysiomorpha
Group Acochlidiacea
Clade Sacoglossa
Group Cylindrobullida
Clade Umbraculida
Clade Nudipleura
Clade Pleurobranchomorpha
Clade Nudibranchia
Clade Euctenidiacea
Clade Dexiarchia
Clade Pseudoeuctenidiacea
Clade Cladobranchia
Clade Euarminida
Clade Dendronotida
Clade Aeolidida
Informal group Pulmonata
Informal group Basommatophora
Clade Eupulmonata
Clade Systellommatophora
Clade Stylommatophora
Clade Elasmognatha
Clade Orthurethra
Informal group Sigmurethra
[edit]Cultural references
In the animated American TV series SpongeBob SquarePants, the main character SpongeBob has a pet sea snail called Gary. Gary makes a "meow" vocalization like a cat. The character's eyes are well-developed and colorful, similar to the eyes of species in the sea snail family Strombidae.
[edit]See also
Freshwater snail
Land snail
Sea slug
Slug |
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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.
The three species of the Giant African land snail Achatina fulica can grow to be 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).
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.
Contents [hide]
1 Types of snails by habitat
2 Slugs
3 Snails in cuisine
4 Agriculture
5 Cultural depictions
6 See also
7 References
[edit]Types of snails by habitat
Main articles: Land snail, Freshwater snail, and Sea snail
[edit]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.
[edit]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.
Snails provide an easily harvested source of protein to many people around the world. 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, southwestern China and parts of the U.S.A.). In certain parts they are fried as satay as for example in Bali, where this dish is known as sate kakul.
[edit]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.[1]
[edit]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.[2][3] Psalms 58:8 uses snail slime as a metaphorical punishment.
Snails were widely noted and used in divination.[2] 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.[4]
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.[5]
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.
[edit]See also
Escargot de Quimper
Gastropod shell
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