Snails are mollusks, which means a kind of animal without backbones. There are two basic kinds of snails: the first includes the snails which have shells; the second, those which are covered merely by a thin mantle. Members of this second group are usually called “slugs.”

All the members of this division of mollusks have one large foot on the underside. Therefore, they are called “gastropods,” or stomach feet. This division also includes the large whelks of the ocean and the periwinkles. The ocean snail measures about 25 millimeters in the shell.