Emilie Ammirati, age 12, of Fargo, N.D., for her question:
HOW MANY KINDS OF SNAILS ARE THERE?
There are more than 50,000 different kinds of marine, freshwater and terrestrial species of mollusk that generally are called "snail." They belong to a classification of animals known as Gastropoda, which literally means "belly footed" animals.
Gastropods have been able to adapt their singular means of locomotion to a wide range of water and land habitats, from the depths and shorelines of oceans to all bodies of fresh water, and from tropical areas to mountains and deserts.
Snails have prominent tentacles on which the eyes are often located. Many snails are as small as four tenths of an inch long while others are as long as two feet.
The spiral shell into which the snail withdraws serves mainly as protection against predators. .The shell also helps the animal to retain body moisture.
Land snails are particularly well adapted to changes in moisture. Some desert species are able to remain sealed within their thick shells for two or more years. Land snail species of more moist habitats usually have thinner shells. Slugs, which live in very moist environments and are often considered snails, have only vestigial shells.
Snails move by means of a wavelike series of muscular contractions along the bottom of the foot. This motion is often aided by cilia and, in land snails, by a track of laid down slime.
Snails feed mainly on algae and decaying matter and are important members of the food web, being a source of food to fish and waterfowl.
A snail browses by means of a radula, a ribbon like tongue often containing many thousands of denticles, or teeth, that are projected from the mouth opening and drawn along rocks or leaves. Some carnivorous snails have radulae that bore holes through the shells of other mollusks to reach the soft flesh.
Many species of snails are hermaphroditic and capable of self fertilization
Escargots, the snails of French cuisine, come from a special type of cultivated land snail called Helix pomatia.
Other edible snails include the abalone of California and Japan (genus Haliotis); the periwinkle of Europe and South Africa (genus Littorina) and the queen conch of the West Indies (genus Trombus gigas).
A few ocean snails are parasites and live in the flesh of starfish or inside living sea animals called corals. Snails may live from two to 20 years. Most land snails have lungs. Some of the fresh water snails have lungs and must come to the surface to breathe the oxygen in the air. Others have gills, which take in oxygen from the water. Most marine or salt water snails have gills.