Identifying common garden molluscs - Is it a slug or a snail?

Garden molluscs » Slug or snail?
Getting started: Is it a slug or a snail? (NOTE: In Scotland slugs are often referred to as snails; no differentiation is made)
Testacella haliotidea

Most European slugs do not have an external shell. The exception is the genusTestacella.

Note the small plate-like shell on the back end, which is much too small for the animal to retreat into. If your specimen looks like this, click on the image right for more information, otherwise click on the image of the slug or snail below, as appropriate.

Typical slug