• Unsegmented soft body• Mollusks have 3 main parts -visceral mass, modified foot, & mantle

• Mollusks have a visceral mass (contains the organs)• Mollusks have a Modified Foot

– Muscular foot and/or tentacles• Have a mantle (fold that wraps around visceral mass

& secretes the shell) • Most have shell (internal or external)

– Or remnants of a shell• Pen in squid

• Body Cavity- true coelom

• Symmetry- bilateral

• Organ systems-

-have organs for circulation, respiration, digestion, excretion, & nervous system

• Respiration- most gills (some snails have simple lung)

• Circulation- 3 chambered heart- most have open circulatory system (but squids & octopuses have closed circ. system)

• Digestion- one way digestive system: separate mouth and anus

• Reproduction- most are separate sexes and reproduce sexually by doing external fertilization (except for snails which are hermaphrodites)

• Nervous- brain, eyes, and nerves

• Excretion- nephridia remove liquid wastes and anus removes solid waste

Tentacles/ modified foot head Mantle

cavityShellfootMantle

Classes of MollusksThere are 7 classes of mollusks but this course will look at the 3 main classes.

• Class Cephalopoda –

octopus and squid

• Class Gastropoda –

slugs and snails

• Class Bivalvia – clams,

mussels, scallops

Class Gastropoda

• Types- snails, conches, limpets free-living; marine, terrestrial, fresh water• noticeable head• single shell, often spiral• muscular foot secretes mucus to form a slimy path to glide along• Feeding-most herbivores that scrape algae off rocks with radula• Mantle- secretes shell

Snail Anatomy

Class Bivalvia• Types- clams, scallops, oysters• marine and freshwater• gill used for gas exchange• all are sessile, filter feeders and filter food

from the water• all have two part shells(bivalves)-Muscular foot- used to dig into sand

Class Cephalopoda•Types- octopus, squid,

cuttlefish • Exclusively marine• Shell- “pen”- internal

remnant of a shell• Use fins and siphon to

move (jet propulsion)• Modified foot= tentacles• Fast swimming predators

-use tentacles to catch prey• Use a beak-like jaw (radula)

to eat prey• Have a special camera like

eye

Ex- Giant Squid

Squid External Anatomy

Siphon

Fins

Mantle

Squid Internal Anatomy