PHYLUM MOLLUSCA

Phylum Mollusca gastropods, bivalves,cephelapods 3 GENERAL BODY REGIONS 1. head- with “brain” or sense organs 2. visceral mass- contains internal organs 3. foot- muscular part of body

Class Gastropoda (stomach-footed) Soft body in CaCO3 shell secreted by mantle Body is bilaterally symmetrical Ventral muscular foot for locomotion Radula- rasping tongue, ribbon of small teeth used to feed on algae “breathe” through gills

HI I’M GARY! I’M SPONGE BOB’S PET SNAIL!

Head-Foot Region The radula is a rasping, protrusible feeding structure found in most molluscs (not bivalves). Ribbon-like membrane with rows of tiny teeth.

Class Gastropoda The shell of a gastropod is always one piece – univalve – and may be coiled or uncoiled. The apex contains the oldest and smallest whorl. Shells may coil to the right or left – this is genetically controlled.

Class Gastropoda Early gastropods had a planospiral shell where each whorl lies outside the others. Bulky Conispiral shells have each whorl to the side of the preceding one. Unbalanced Shell shifts over for better weight distribution.

Class Gastropoda Many snails can withdraw into the shell and close it off with an operculum.

ABALONE SNAILS LIMPETS CONCH NUDIBRANCH (sea slugs) gastropods that have lost their shell CONE SNAIL (car nivorous)

Class bivalvia Clams, oysters, mussels Laterally compressed body enclosed in two shells(valves) joined at a hinge, controlled by strong muscles Gills used for getting 02 and filter feed No head or radula

CLAMS- use foot to burrow in sediment CLAMS- use foot to burrow in sediment. Uses siphon to draw in water for O2 and food.

Largest bivalve- giant clam up to 3ft in length! (Tridacna gigas) *symbiotic zooxanthella help its size

SCALLOPS- some can swim by ejecting water rapidly out siphon MUSSELS- not burrowers, secrete strong byssal threads to attach to surfaces OYSTERS- cement their shells to a hard surface, sometimes to other oysters SCALLOPS- some can swim by ejecting water rapidly out siphon GEODUCK

PEARL OYSTERS- when there’s an irritant or parasite in the mantle, shiny layers of nacre coats it to form pearl in some * Most pearls we encounter are cultured pearls

Class Bivalvia Scallops have a row of small blue eyes along the mantle edge.

Class Bivalvia Native freshwater clams in the U.S. are jeopardized. Of more than 300 species once present, 12 are extinct, 42 are endangered and 88 more are of concern. Sensitive to water quality changes, Zebra mussels are a serious exotic invader into the Great Lakes Region.

Class cephalopoda (“head-footed”) Octopuses, squids, cuttlefish Active lifestyles, agile swimmers Complex nervous system, eyes similar to ours Reduction/loss of shell Foot is modified into tentacles/arms with suckers

Nautilus Last living type of externally-shelled cephalopod Don’t exhibit many other squid/octopus-like qualities “Swimming snail”

“Jet-propulsion” of water, controlled by flexible siphon, for quick movement Fans out body in defense

OCTOPUSES- 8 long arms, lack shell, bite prey (crabs, lobsters, shrimp) with beak-like jaws Distract predators by emitting cloud of dark fluid produced by ink sac

SQUID- better swimmers, elongated body, two triangular fins, 8 arms and two tentacles w/suckers circling mouth, shell reduced to stiff pen

Colossal squid- largest invertebrate, hooks on tentacles GIANT SQUID: up to 60ft in length, teeth on suckers.

CUTTLEFISH: have calcified internal shell that helps in bouyancy and gives its shape (cuttle bone) Look like squid but have fin running along sides

CAMOUFLAGE Chromatophores-Red, brown, yellow pigments under skin controlled by muscles Light reflectors under skin Muscles able to change texture