Helix (genus)
378787
212130785
2008-05-13T15:46:33Z
Apokryltaros
318802
/* Respiration */
{{Taxobox
| name = Helix
| image = Snail1web.jpg
| image_width = 230px
| image_caption = Garden snail (''[[Helix aspersa]]'') on ''[[Limonium]]''
| regnum = [[Animal]]ia
| phylum = [[Mollusca]]
| classis = [[Gastropoda]]
| ordo = [[Pulmonata]]
| familia = [[Helicidae]]
| genus = '''''Helix'''''
| subdivision_ranks = Species
| subdivision =
See text.
}}
'''''Helix''''' is a [[genus]] of terrestrial [[Pulmonata|pulmonate]] [[snail]]s native to [[Europe]] and the regions around the [[Mediterranean Sea]]. ''Helix'' snails have been introduced throughout the world, where some, especially ''H. aspersa'', have become garden pests. ''Helix'' is the [[type genus]] of the family [[Helicidae]]. The most well known [[species]] include ''[[Helix aspersa]]'' the Common, or Brown Garden Snail, and ''[[Helix pomatia]]'', the [[Escargot]], Roman Snail, Burgundy Snail, or Edible Snail.
== Species ==
*''[[Helix albescens]]'' Rossmaessler, 1839
*''[[Helix aperta]]'' Born, 1778
*''[[Helix aspersa]]'' Müller, 1774 - Brown Garden Snail, Common Garden Snail
*''[[Helix ceratina]]'' (Shuttleworth, 1843) <ref>Bouchet, P. 1996. Helix ceratina. In: IUCN 2006. 2006 IUCN Red List of Threatened Species. <www.iucnredlist.org>. Downloaded on 2 April 2007. http://www.iucnredlist.org/search/details.php/9843/summ</ref>
*''[[Helix engaddenis]]'' Bourguinat, 1852
*''[[Helix godetiana]]'' <ref>Mylonas, M. 1996. Helix godetiana. In: IUCN 2006. 2006 IUCN Red List of Threatened Species. <www.iucnredlist.org>. Downloaded on 2 April 2007. http://www.iucnredlist.org/search/details.php/9844/summ</ref>
*''[[Helix lucorum]]'' Linnaeus, 1758
*''[[Helix lutescens]]'' Rossmässler, 1837
*''[[Helix melanostomata]]'' Draparnaud, 1801
*''[[Helix obruta]]'' Morelet, 1860 <ref>Frias-Martin, A. 1996. Helix obruta. In: IUCN 2006. 2006 IUCN Red List of Threatened Species. <www.iucnredlist.org>. Downloaded on 2 April 2007. http://www.iucnredlist.org/search/details.php/9845/summ</ref>
*''[[Helix pomatia]]'' Linnaeus, 1758 - Burgundy Snail, Roman Snail, Edible Snail
*''[[Helix texta]]'' Mousson, 1861 <ref>Heller, J. 1996. Helix texta. In: IUCN 2006. 2006 IUCN Red List of Threatened Species. <www.iucnredlist.org>. Downloaded on 2 April 2007. http://www.iucnredlist.org/search/details.php/9846/summ</ref>
*''[[Helix vermiculata]]''
Comment: Some taxonomists remove the following species "''Helix aperta''", "''Helix aspersa''", and "''Helix vermiculata''" from genus ''Helix'' and place them in their own monotypic genera as ''[[Cantareus apertus]]'', ''[[Cornu aspersum]]''<ref>[http://www.weichtiere.at/english/gastropoda/terrestrial/escargot/cornu.html The Cornu Problem]</ref> and ''[[Eobania vermiculata]]''. ''Helix subplicata'' is a synonym for ''[[Idiomela subplicata]]''.
== External features ==
[[Image:Common snail.jpg|thumb|right|225px|Common snail (''Helix aspersa'')]]
In addition to the hard calcareous [[animal shell|shell]] that covers and protects the internal organs, the head and foot region can be observed when the snails are fully extended. When they are active, the organs such as the [[lung]], [[heart]], [[kidney]] and [[intestines]] remain inside the shell; only the head and foot emerge.
The head of the snail has two pairs of tentacles: the upper and larger pair contain the eyes, and the lower pair are used to feel the ground in front. The mouth is located just underneath the head. The tentacles can be withdrawn or extended depending on the situation. The mouth has a unique [[tongue]] called a "[[radula]]" that is composed of many fine chitinous [[teeth]]. This serves for rasping and cutting food.
From April and throughout the summer, the number of snails [[copulation|copulating]] increases due to the high temperature and humidity which enhances the possibility of oviposition. The Pulmonate snails are [[hermaphrodite|hermaphroditic]], meaning that both female and male [[sexual organ]]s are present in the same individual. The snails produce both [[egg (biology)|eggs]] and [[sperm]] in the ovotetis (also called the hermaphrodite gland), but it is later separated into two divisions, a sperm duct and [[oviduct]], respectively.
[[Mating]] takes several hours, sometimes a day. ''H. aspersa'' snails stab a calcite spine, termed a "love dart" at their partner, which contains a chemical that enables more than twice as many sperm to survive inside the recipient. A few days after mating, the eggs are laid in the soil. They are usually 4-6 mm in diameter.
After snails are hatched from the egg, they mature through one or more years. It depends on where the organism lives. Maturity takes two years in Southern [[California]], while it takes only ten months in [[South Africa]].
The size of the adult snails slightly varies with species. ''H. aspersa'' grows up to 35 mm in height and width, whereas ''H. pomatia'' grows up to 45 mm. The life span of snails in the wild is on average two or three years.
Some snails may live longer, perhaps even 30 years or older in the case of the Roman snail<ref>[http://www.weichtiere.at/Mollusks/Schnecken/weinberg.html The Roman Snail, ''Helix pomatia'']</ref> but most live less than 8 years. Many deaths are due to predators and [[parasite]]s.
The garden snail is a relatively fast snail. It has been observed to reach speeds of up to 1.3 cm/s.<ref>{{cite web|url=http://hypertextbook.com/facts/AngieYee.shtml|title=Speed of a Snail|first=Angie|last=Yee|year=1999|work=The Physics Factbook}}</ref>
== Respiration ==
[[Image:Snail.jpg|thumb|right|225px|Burgundy Snail (''Helix pomatia'')]]
Since snails in the genus ''Helix'' are terrestrial rather than fresh-water or marine, they have developed a simple lung for respiration. (Most other snails and gastropods have [[gill]]s, instead.)
[[Oxygen]] is carried by the blood pigment [[hemocyanin]]. Both oxygen and [[carbon dioxide]] diffuse in and out of blood through the [[capillaries]]. A [[muscle|muscular]] valve regulates the process of opening and closing the entrance of the lung. When the valve opens, the air can either leave or come into the lung. The valve plays an important role in reducing water loss and preventing drowning.
== Ecology ==
Snails prefer cool, damp environments, as they easily suffer from moisture loss. Snails are most active at night and after [[rainfall]]. During unfavourable conditions, a snail will remain inside its [[animal shell|shell]], usually under [[rock (geology)|rocks]] or other hiding places to avoid being discovered by [[predator]]s. In dry [[climate]]s snails will naturally congregate near water sources, including artificial sources such as waste-water outlets of [[air conditioner]]s.
The common garden snail (''Helix aspersa'') is [[herbivore|herbivorous]]. These snails are able to digest most vegetation including [[carrot]]s and [[lettuce]]. They also have a specialized crop of symbiotic [[bacterium|bacteria]] that aid in their digestion, especially with the breakdown of the polysaccharide [[cellulose]] into simple sugars.
There are many [[predator]]s, both specialist and generalist, that feed on snails. Some animals, such as the [[song thrush]], break the shell of the snail by hammering it against a hard object, such as stone, in order to expose its edible insides. Other predators, such as some species of [[frog]]s, circumvent the need to break snail shells by simply swallowing the snail whole, shell and all.
Some carnivorous species of snails, such as the [[decollate snail]], and the rosy wolf snail, ''[[Euglandia rosea]]'', also prey on ''Helix'' snails. Such carnivorous snails are also commercially grown and sold in order to combat pest snail species. Many of these also escape into the wild, where they prey on indigenous snails, such as the Cuban land snails of the genus ''[[Polymita]]'', and the indigenous snails of [[Hawaii]].
==Edible snails==
{{seealso|Snail#Human use: land snails as food}}
''H. pomatia'' and ''H. aspersa'' are the two edible species most used in European [[cuisine]]. Spanish cuisine also uses ''Otala punctata'', ''Theba pisana'' and ''Iberus gualterianus alonensis'', amongst others. [[Escargot]]s are snails served in a traditional way as [[appetizer]]s. They may also be used as ingredients in other recipes.
Snails contain many [[nutrients]] and are very rich in [[calcium]] and also contain [[vitamin B1]] and [[vitamin E|E]]. They also supply various kinds of essential [[amino acid]]s. Also, they are low in [[calorie]]s and [[fat]].
==See also==
{{commonscat|Helix}}
[[Heliciculture]]
==References==
{{reflist}}
==External links==
* [http://www.petsnails.co.uk/ Helix snails in captivity]
[[Category:Helicidae]]
[[fr:Helix]]
[[pt:Helix]]
[[sv:Helix (släkte)]]