The Gastropoda or gastropods are a large taxonomic class within the molluscs, a group of animals that are more commonly known as snails and slugs. The class includes snails and slugs of all kinds and all sizes: huge numbers of marine snails and sea slugs, as well as freshwater snails and freshwater limpets, and the terrestrial (land) snails and slugs. The class Gastropoda contains a vast total of named species, second only to the insects in overall number. The fossil history of this class goes all the way back to the Late Cambrian. There are 611 families of gastropods, of which 202 families are extinct, being found only in the fossil record.