They have a single, coiled shell. A pair of sensory tentacles come off their head with eyes at the end. Their mouth has a rasping tongue, called the radula, to shred food. Most eat plants (including algae) but some eat dead animals. Parasitic worms may live in them. Snails move by a muscular, slimy foot under their body. Algae naturally grows on most aquatic snails. It provides some camouflage.
Snails are both male and female. All snails can lay eggs. They can "mate" with themselves and thus only one can reproduce in an aquarium or pond. Most snails lay eggs but some, like the trapdoor snail, give live birth.
There are two types of snails. Gilled snails have gills and can close their bodies into their shells with a plate, or door. Gilled snails usually lay their eggs in jelly-like cocoons above or under water. The trapdoor snail (actually a livebearer) and apple snail are two of these. Pulmonate snails have lungs. They either come to the surface to breathe, or some breathe through their body surface while underwater. They cannot close their bodies into their shells. Pulmonate snails usually lay their eggs in gelatinous masses under water (the Malaysian trumpet snail though is a live-bearer). Examples are pond snails and ramshorn snails.
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