I don't know why you put "the six kindgoms" in the details.
There's more than one kind of snail, but you're probably referring to the small little guys that you find in the dirt in Canada and many parts of the U.S (and many other places). Like the common garden snail.
If you are asking about the garden snail, then it's actual name is Helix aspersa. If you mean all snails in general, then they're usually called gastropods, since they belong to class Gastropoda.