Gastropoda "The class Gastropoda or the gastropods, also previously known as gasteropods, or univalves, and more commonly known as snails and slugs, are the most diversified class in the phylum of mollusks, with (60,000-75,000) to 80,000 known living species. There are 409 recent families of gastropods, but fossils have been classified as showing 202 further families. This class of animals is second only to insects in its number of known species." Source and further information: http://en.wikipedia.org/wiki/Gastropoda "About 786 distinct living species of cephalopods have been identified." http://en.wikipedia.org/wiki/Cephalopoda "Bivalves are molluscs belonging to the class Bivalvia. They have two-part shells, and typically both valves are symmetrical along the hinge line. The class has 30,000 species, including scallops, clams, oysters and mussels. Other names for the class include Bivalva, Pelecypoda, and Lamellibranchia." http://en.wikipedia.org/wiki/Bivalvia "Chitons are small to large, primitive marine mollusks in the class Polyplacophora. There are 900 to 1,000 extant species of chitons in the class, which was formerly known as Amphineura)." http://en.wikipedia.org/wiki/Chiton