Phylum_Mollusca

Phylum Mollusca The molluscs rival the arthropods in their diversity of body forms and sizes, as well as their ecological success. The phylum also provides some of the most familiar animals, such as snails , clams , mussels , squids , and octopus (which, like the arthropods , are well known because they're good to eat). The phylum Mollusca also includes lesser known forms such as the chitons , tusk shells, solenogasters , among others. Approximately 50,000 species of Molluscs have been described, and because of the shelled forms they have left a rich fossil record. However, the earliest molluscs probably arose in the Precambrian , and nothing is known about what they were like. Systematic summary for the phylum Mollusca : Class Gastropoda ( snails, sea slugs) Class Pelecypoda (=Bivalvia: clams, mussels, oysters, scallops) Class Cephalopoda (squids, octopus, nautilus, cuttlefish) Class Aplacophora Class Monoplacophora Class Polyplacophora (chitons) Class Scaphopoda (tusk shells) Class Caudofoveata CLASSES OF MOLLUSCS Class Gastropoda Hermissenda crassicornis , Nudibranch (sea slug),class Gastropoda , Order Nudibranchia , from McFarland, 1966. Most of the approximately 40,000 living species of gastropods have shells, however there are quite a few groups that have either reduced or internal shells, class, species, forms, shells, shell, marine, known, molluscs, living, however, described, approximately, about, tusk, sea, bivalves, squid, small, scaphopoda, polyplacophora, octopus, found, deep, animals, terrestrial, tentacles, squids, sp, snails, slugs, pratt, phylum, pelecypoda, organisms, mussels