Gastropoda

slugs, snails, nudibranchs

have large fleshy foot for locomotion, rasp-like mouth called radula which is developed for grazing, harpooning or drilling in different groups, gills for gas exchange

Polyplacophora

chitons

shell made of 7-8 chitinous plates (external or internal) to allow for mobility, like armor, locomotive foot, gills for gas exchange

Bivalvia

clams, mussels, oysters, scallops

two shells hinged along one end to protect soft body, foot for locomotion or digging, gills for gas exchange and capturing food, because the shell is closed, pearls are produced when a foreign particle enters and the animal secretes from its mantle to cover the invader

Cephalopoda

octopus (no shell), squid (internal shell), cuttlefish (internal shell), nautilus (external shell), with foot modified into tentacles for manipulating prey and locomotion, gills for gas exchange, beaks for tearing food, swim by jet propulsion, well-developed senses, ability to change appearance based on environment and solve multi-step problems