How are mullusks classified?

There are 93,000 named species of mollusk. Mollusks belong to the phylum Mollusca. There are four main classes of mollusk: 1) Cephalopoda; four types; Octopi, squids, cuttle fish, and the chambered nautilis 2) Bivalvia; four types; clams, oysters, scallopes, and muscles 3) Gastropada; gastropadas are snails and slugs 4) Polyplacophora; polyplacophora are chitons.