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 cavity Shell footMantle

Classes of Mollusks There 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