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The name snail applies
to most members of the molluscan Class Gastropoda that have coiled
shells. Other gastropods, which lack a conspicuous shell, are
commonly called slugs, and are scattered throughout groups that
primarily include snails. Snails are found in freshwater, marine,
and terrestrial environments. While most people are familiar with
only terrestrial snails, the majority of snails are not terrestrial.
Snails with lungs belong to the group Pulmonata, while those with
gills belong to the Snails move like worms by alternating body
contractions with stretching, with a proverbially low speed (hence
the term snail mail for postal services). They produce mucus in
order to aid locomotion by reducing friction. The mucus also reduces
the snail's risk of injury and helps keep away potentially dangerous
insects like ants. When retracted into their shells, snails cover
the entrance with a 'trapdoor' like structure called an operculum.
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In winter some
snail species hibernate in their shells by closing the opening
with a thin shell-like plate that they build only for this use
and destroy in spring. Even some slug species build a shell-like
object below their upper skin. Snails come in a range of different
sizes. The largest land snail is the Giant African Snail (Achatina
fulica; Family Achatinidae), which can measure up to 30cm. Pomacea
maculata (Family Ampullariidae), or Giant Apple Snail is the largest
freshwater snail, with its size reaching 15 cm diameter and over
600 g weight. The biggest of all snails is Syrinx aruanus, a marine
species living in Australia. Shell lengths up to 1 m have been
reported.
Images 1 to
3 Are Courtesy Of The U.S. Fish & Wildlife Service
Image Number 4 Courtesy Of The National Undersea Research Program
Image Number 5 Comes From pdphoto.org
Image Number 6 Is Courtesy Of The U.S.D.A.
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