Helix (genus)
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 Garden snail (Helix aspersa)
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Helix is a genus of common snails. It belongs to the family Helicidae. The most well known species are: Helix aspersa (Brown Garden Snail), Helix pomatia (Roman Snail, Burgundy Snail, or Edible Snail).
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[edit] Species
- Helix aperta Born, 1778
- Helix aspersa Mûller, 1774 Brown Garden Snail, Common Garden Snail
- Helix engaddenis Bourguinat, 1852
- Helix lucorum Linnaeus, 1758
- Helix lutescens Rossmässler, 1837
- Helix melanostomata Draparnaud, 1801
- Helix pomatia Linnaeus, 1758: Burgundy Snail, Roman Snail, Edible Snail
- Helix vermiculata
Comment: According to some taxonomists, "Helix aperta", "Helix aspersa", and "Helix vermiculata" are not members of the Helix genus. They are called Cantareus apertus, Cornu aspersum [1] and Eobania vermiculata.
[edit] External features
In addition to the hard calcareous 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 The tentacles can be withdrawn or extended depending on the situation.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 copulating increases due to the high temperature and humidity which enhances the possibility of oviposition. The Pulmonate snails are hermaphrodite, meaning that both female and male sexual organs are present in the same individual. The snails produce both 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 fire a 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 [2] but most live less than 8 years. Many deaths are due to predators and parasites.
The garden snail is a relatively fast snail. It has been observed to reach speeds of up to 1.3 cm/s.[3]
[edit] Respiration
Since snails in the Helix genus are terrestrial rather than fresh-water or marine, they have developed a simple lung for respiration. Many other snails that belong to the class Gastropoda have gills instead.
Oxygen is carried by the blood pigment hemocyanin. Both oxygen and carbon dioxide diffuse in and out of blood through the capillaries. A 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.
[edit] 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 shell, usually under rocks or other hiding places to avoid being discovered by predators. In dry climates snails will naturally congregate near water sources, including artificial sources such as waste-water outlets of air conditioners.
The common garden snail (Helix aspersa) is herbivorous. These snails are able to digest most vegetation including carrots and lettuce. They also have a specialized crop of symbiotic bacteria aiding the digestion (breakup into sugars) of cellulose.
There are many predators feeding upon 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 certain species of frogs, eat snails without ever damaging their shells.
Some carnivorous species of snails, such as the Decollate snail, also exist.
[edit] Edible snails
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. Escargots are snails served in a traditional way as appetizers. 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 E. They also supply various kinds of essential amino acids. Also, they are low in calories and fat.
[edit] See also
