Slug

Description:

Slug is a common name for an apparently shell-less terrestrial gastropod mollusk. The word "slug" is also often used as part of the common name of any gastropod mollusc that has no shell, has a very reduced shell, or has only a small internal shell. (This is in contrast to the common name "snail", which is applied to gastropods that have a coiled shell that is large enough that the soft parts of the animal can retract fully into it.) Slugs exist on land and in the sea, and there is even one genus of freshwater slugs, Acochlidium. The unadorned word "slug" is however applied primarily to land slugs, whereas slugs from the sea or from freshwater are usually referred to as "sea slugs" and "freshwater slugs". Land gastropods with a shell that is not quite vestigial, but is too small to retract into (like many in the family Urocyclidae), are known as semislugs.