Are slugs snails but without the shells?
Slugs are gastropod molluscs without shells or with very small internal shells, in contrast to snails, which have a prominent coiled shell. The loss or reduction of the shell is a derived character, and the same basic body design has independently evolved several times, making slugs a polyphyletic group. Although they undergo torsion (180 degree twisting of internal organs) during development, their bodies are streamlined and worm-like, and so show little external evidence of it. Slugs include both marine and terrestrial species. The main group of marine or sea slugs are the nudibranchs. However, the ecological information in the article below applies mainly to land slugs. The soft, slimy bodies of slugs are prone to desiccation, so land-living slugs are confined to moist environments.
