Snails and limpets have a single coiled, one piece shell. New shell growth is on the outermost part of the coil. Some shells are round and flat and some are like a cone with a point. Slugs are basically snails that don't have a shell. Some slugs are more closely related to snails than other slugs.
Snails have a distinct head with a pair of tentacles, that extend and retreat. The eyes are at the base of the tentacles. They have round mouths with a row of teeth that are replaced as they wear down. Snails also have a tongue called a radula. Snails have a muscular foot with slime glands. The slime aids them while they crawl on their foot.
Most snails feed on dead plants and animals, though some can become pests feeding on plants, and a few are even carnivorous.
In the aquarium snails will usually show up whether you want them there or not, unless you take special precautions to keep them out. The snails most likely to show up are ramshorns, pond snails or Malayan livebearing snails. Snails usually prefer hard water as their shells can't develop well in most soft water, though they can be given calcium supplements to help with shell growth.
Snails are generally placed in to 2 groups; those with gills and those that use lungs to breath. Gilled snails are also called prosobranchs. Snails with lungs are called pulmonates.
The most commonly seen aquarium snails are pulmonate snails. These include the common pond snail and ramshorn snails. Pulmonate snails have developed lungs and are related. It's believed that the pulmonate snails that live on the land evolved from marine snails. The pulmonate snails that live in water now evolved from those that had developed lungs on land. Slugs are pulmonate snails that don't have shells.
Pulmonate snails are hermaphroditic but not all of them in the same way. Some species change sex, some fertilize their own eggs and some cross fertilize. These snails lay eggs in gelatin masses attached to submerged rocks, plants and other surfaces.
Prosobranchs are gilled snails consisting of a very large group of many different snails that include both marine and fresh water snails. The freshwater snails in this group are believed to have evolved from marine snails. Gilled snails often have an operculum. An operculum is a door like plate attached to the foot of the snails.
The most commonly seen gilled snail in the aquarium is the Malayan livebearing snail. The other gilled snails used in the aquarium are larger and used for algae control. Many of them are very attractive and come in different shapes and colors. Most can also be bred in the aquarium. These larger snails are usually purchased through your local aquarium store or through mail order services. Some of the larger snails will fare better if given algae wafers, zucchini or other lightly cooked vegetables.
For more information on snails:
Malayan Livebearing Snails
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| Moss Animals
| Leeches, Worms, and Planaria
| Small Crustaceans
| True Bugs
| Ramshorn Snails
| Pond Snails
| Malayan Livebearing Snails