Mollusca
Mollusca is a large phylum of invertebrate animals whose members are known as molluscs or mollusks. Around 85,000 extant species of molluscs are recognized. The number of fossil species is estimated between 60,000 and 100,000 species
Structures
Molluscs have soft bodies and hard outer shells, their body is made of 4 main parts: the foot, visceral mass, mantle, and shell.
Classes
Gastropods - snails and slugs, shell protects body, usually have a distinct head with eyes at the ends of tentacles, embryo undergo torsion,
Bivalves - clams, oysters, mussels, scallops. shell has 2 halves held together by a very strong muscle. Most are suspension feeders.
Cephalopods - squids and octopus. squids can swim backwards.