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.

SNAILS

LIMPETS ABALONE

CONE SNAIL

(carnivorous)

CONCH

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.

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

OYSTERS- cement

their shells to a hard

surface, sometimes to

other oysters

MUSSELS- not burrowers, secrete strong

byssal threads to attach to surfaces

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

Living fossil; not much has changed in millions of

years

Shell for protection with gas trapped in chambers

for bouyancy

90 suckerless tentacles

“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

calcified internal shell that helps in bouyancy

and gives its shape (cuttle bone)

Short lifespan (~3yrs)

Males have elaborate courtship display

Kaleidoscopic changes of color

CEPHALOPOD CAMOUFLAGE

Chromatophores-Red, brown, yellow pigmented

cells under skin controlled by muscles

CEPHALODPOD CAMOUFLAGE

Iridophores-Light reflecting pigment cells

under skin (cause flash-like mirror)

Photophores- responsible

for bioluminescence in squid

CEPHALOPOD CAMOUFLAGE

Octopus and cuttlefish can control muscles

to change skin texture to match surroundings

Instant changes due to long neurons

TYPES OF……

BLUE RINGED OCTOPUS- highly

toxic saliva it releases into water or

injects to captured prey

GIANT OCTOPUS- up to 30ft and

one of most intelligent. Can

navigate a maze and remember

long term.

TYPES OF……

DUMBO OCTOPUS- lives in the deep, not

much known other than unusual earlike

flaps extending from mantle