Phylum Molluska Over 50,000 speciesOver 50,000 species Coelomate, Protostomes, Bilaterally symmetricalCoelomate, Protostomes, Bilaterally symmetrical Mostly marine, although some live in fresh water or land.Mostly marine, although some live in fresh water or land. Generally soft-bodied with a hard shellGenerally soft-bodied with a hard shell However, squid & octopi have internalized, reduced or lost their shells.However, squid & octopi have internalized, reduced or lost their shells. Body PlanBody Plan Although phenotypically diverse, mollusks share 3 common featuresAlthough phenotypically diverse, mollusks share 3 common features A muscular foot - usually for movementA muscular foot - usually for movement A visceral mass - including internal organsA visceral mass - including internal organs A mantle - envelopes visceral mass and secretes a shellA mantle - envelopes visceral mass and secretes a shell

Molusk General Anatomy

Class Polyplacophora (chitons) Marine animals - shells divided into 8 platesMarine animals - shells divided into 8 plates Move using a muscular foot and graze using a scraping mouthpart called a radulaMove using a muscular foot and graze using a scraping mouthpart called a radula

Chiton Anatomy

Chitons

Class Bivalvia Include clams, oysters and musselsInclude clams, oysters and mussels Have shells divided into 2 halves, connected by strong musclesHave shells divided into 2 halves, connected by strong muscles Has hatchet shaped foot for digging and anchoringHas hatchet shaped foot for digging and anchoring Are typically filter feeders drawing in water end expelling it through a siphon tubeAre typically filter feeders drawing in water end expelling it through a siphon tube Generally sessile, however, some species can quickly move by rapidly closing it's shellGenerally sessile, however, some species can quickly move by rapidly closing it's shell

Bivalve Anatomy

Bivalves

Class Gastropoda Include snails, abalone, and slugsInclude snails, abalone, and slugs Largest class of mollusks ~40,000 speciesLargest class of mollusks ~40,000 species Exhibit embryonic process of torsionExhibit embryonic process of torsion Visceral mass twists during developmentVisceral mass twists during development Most species are herbivores, but some have modified radullas for boring into other mollusksMost species are herbivores, but some have modified radullas for boring into other mollusks Some species have successfully colonized landSome species have successfully colonized land

Gastropods

Giant African Land Snail

Class Cephalopoda Unlike other mollusks, these are quick predatorsUnlike other mollusks, these are quick predators Have beak-like jaws and poison to catch & immobilize preyHave beak-like jaws and poison to catch & immobilize prey Beak is the center of several long tentaclesBeak is the center of several long tentacles Foot has been modified to form a siphon which allows most species to move quickly using a jet of water.Foot has been modified to form a siphon which allows most species to move quickly using a jet of water. Only mollusks with a closed circulatory system (blood is always contained in vessels)Only mollusks with a closed circulatory system (blood is always contained in vessels) Very highly developed nervous systemVery highly developed nervous system Can learn complex behaviorsCan learn complex behaviors Octopi have learned to open jars to retrieve preyOctopi have learned to open jars to retrieve prey May have rudimentary communicationMay have rudimentary communication Cuttlefish and octopi may communicate by skin colorationCuttlefish and octopi may communicate by skin coloration

Cephalopod Anatomy

Octopus

Squid

Cuttlefish

Cambered Nautilus