Helix (genus)
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| Image:Snail1web.jpg Garden snail (Helix Aspersa) | ||||||||||||
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The Genus Helix belongs to the Family Helicidae. The most well known species are: Helix aspersa (Brown Garden Snail), Helix pomatia (Roman Snail, Burgundy Snail, and the Edible Snail).
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Where snails are naturally found
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.
What snails eat and who eats snails
The common garden snail (Helix aspersa) is herbivorous. They are able to digest most vegetation such as carrots and lettuce. They also have a specialized crop of symbiotic bacteria in their intestine which is used to digest cellulose.
There are many predators that prey upon snails. Some animals such as the song thrush break the shell of the snail by hammering it against a stone to get at its soft insides, some, like frogs, even eat the whole snail, shell and all. There are even some snails such as the Decollate snail that prey upon other snails.
Many Europeans enjoy eating snails. Helix pomatia is the one of the best known edible snails. In addition to the excellent taste of the snails, they have 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.
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, 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 The tentacles can be withdrawn or extended depending on the situation.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 unique tongue called a "radula" that is composed of many fine chitinous teeth. This serves for rasping and cutting food.
Mating
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 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. A few days later, the eggs are laid in the soil. They are usually 4-6 mm in diameter.
Growth and death
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 the snails in the wild is on average two or three years.
Some snails many live longer, but no more than eight years. Many deaths are due to predators and parasites.
Respiration
Snails in the Helix genus are terrestrial rather than in being fresh water or marine, they have mangaed this by having developed a simple lung. Many other snails that belong to the class Gastropoda have gills instead.
Oxygen is carried by the blood pigment, haemocyanin. 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.
Taxonomy
- Helix aperta Born, 1778
- Helix aspersa Mûller, 1774 Brown Garden Snail, Common Garden Snail
- Helix engaddenis Bourguinat, 1852
- Helix lucorum Linnaeus, 1758
- Helix melanostomata Draparnaud, 1801
- Helix pomatia Linnaeus, 1758: Burgundy Snail, Roman Snail, Edible Snail
- Helix vermiculata
