slug

Any of various terrestrial gastropod mollusks having a slow-moving slimy elongated body with no shell or with a flat rudimentary shell on or under the skin, usually found in moist habitats.

A sea slug.

The smooth soft larva of certain insects, such as the sawfly.

A slimy mass of aggregated amoeboid cells that develops into the spore-bearing fruiting body of a cellular slime mold.

A sluggard.