Snails And A Baby

Gastropod species which lack a conspicuous shell are commonly called slugs rather than snails, although, other than having a reduced shell or no shell at all, there are really no appreciable differences between a slug and a snail except in habitat and behavior. A shell-less animal is much more maneuverable and compressible, and thus even quite large land slugs can take advantage of habitats or retreats with very little space, squeezing themselves into places that would be inaccessible to a similar-sized snail, such as under loose bark on trees or under stone slabs, logs or wooden boards lying on the ground.
Taxonomic families of land slugs and sea slugs occur within numerous larger taxonomic groups of shelled species. In other words, the reduction or loss of the shell has evolved many times independently within several very different lineages of gastropods, thus the various families of slugs are very often not closely related to one another.