Mollusk Characteristics Unsegmented soft body Mollusks have 3 main parts Visceral mass: contains the internal organs Modified Foot: –Muscular foot and/or tentacles Mantle: fold that wraps around visceral mass & secretes the shell Most have shell (internal or external) –Or remnants of a shell

Mollusk Characteristics 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 snails which are hermaphrodites) Nervous- ganglia, eyes, and nerves Excretion- nephridia remove wastes

Classes of Mollusks There are 7 classes of mollusks but this course will look at the 3 main classes. Class Cephalopoda – “head-foot” octopus and squid Class Gastropoda – “stomach-foot” slugs and snails Class Bivalvia – “two shells” clams, mussels, scallops

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

OCTOPUS Octopus in Aquarium

SQUID

NAUTILUS

Cuttlefish Cuttlefish Video

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- toothed tongue Mantle- secretes shell

SNAIL

SLUG Sea slugs- reproduction

CONCH

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

CLAM

OYSTER

MUSSEL

SCALLOPS

Squid External Anatomy Siphon Fins Mantle

Squid Internal Anatomy

Gills Reproductive Organs Siphon Fins