Land snails abound in tropical jungles and in damp temperate regions. All of them need calcium carbonate for building their shells, and so are not common in sandy soil. Slugs differ from snails in that they generally have only a small internal shell. Snails move by sliding on their single foot. Specialized gland in the foot secrete mucus, which lubricates the path over which the snail crawls.
Snails can only crawl.
Even those that live in water can't swim. As they crawl they secrete a slime to help themselves move across surfaces. The snail's head bears the mouth opening and one or two pairs of tentacles. The eyes are located at the base of the tentacles. Most snails live off plants and dead organic matter, although a few are carnivorous.