Your pet snail, Sammy, is one example of a mollusk, or a soft, spineless animal. In Sammy's case, he has a shell, though some mollusks don't.
It's a bit ironic that this term for a large phylum of invertebrates comes from a Latin word that means "soft," mollis, since many mollusks (or molluscs in Britspeak) have hard shells. The epithet comes from the nature of the creatures' bodies, whether in shell (like a snail) or without (like a slug).
