The Gastropoda form a class within the phylum Mollusca. Known informally as gastropods, they are sometimes referred to as univalves, although the term is misleading since the shell does not truly function as a valve, unlike the paired shells of pelecypods (Bivalvia) which in a way do. Gastropods are more commonly known as snails and slugs. Image:Bucanopsis leda.jpg This prehistoric mollusc-related article is a stub. You can help Fossil Wiki by [ expanding it].