Limacology (from Latin limax, "slug", and Greek -λογία, -logia) is the branch of zoology which deals with slugs, i.e. shell-less gastropod mollusks. A person that studies limacology is referred to as a limacologist.
However, slugs are an extremely polyphyletic group, thus "limacology" is not a taxonomically accurate term, and it is now rarely used.
References
Limacology Wikipedia(Text) CC BY-SA