MOLLUSCAMOLLUSCA

CharacteristicsCharacteristics

• Class Gastropoda – Class Gastropoda – snails, slugssnails, slugs

• Class Cephalopoda – Class Cephalopoda – octopus, squid, nautilusoctopus, squid, nautilus

• Class Bivalvia – Class Bivalvia – oysters, clamsoysters, clams

• Soft body covered by Soft body covered by shell (usually)shell (usually)

• Bilateral symmetryBilateral symmetry• Word mollusca means Word mollusca means

“soft”“soft”

AnatomyAnatomy

• One way digestive One way digestive system – mouth to anussystem – mouth to anus

• CoelomatesCoelomates• Open circulatory Open circulatory

system in gastropods system in gastropods and bivalves- blood and bivalves- blood sloshes around body sloshes around body cavitycavity

• Closed circulatory Closed circulatory system in cephalopodssystem in cephalopods

• Gills for respiration on Gills for respiration on mollusks that live in mollusks that live in waterwater

AnatomyAnatomy

• Mollusks have Mollusks have strong muscles to strong muscles to help them move help them move and swimand swim

• The skeleton of The skeleton of most mollusks is a most mollusks is a shell, but not all shell, but not all mollusks have a mollusks have a shellshell

AnatomyAnatomy• Gastropods and Gastropods and

Bivalves have a simple Bivalves have a simple nervous system and nervous system and Cephalopods have a Cephalopods have a complex nervous complex nervous systemsystem

• Mollusks cover their Mollusks cover their bodies with skin and bodies with skin and shells. Most mollusks shells. Most mollusks have to keep their skin have to keep their skin moist.moist.

AnatomyAnatomy

• Mollusks all have a Mollusks all have a “foot”. In bivalves “foot”. In bivalves this is the soft inside this is the soft inside of the clam. In of the clam. In gastropods, they use gastropods, they use their foot to move their foot to move along the ground. In along the ground. In cephalopods, the cephalopods, the foot has been foot has been adapted to be the adapted to be the mantle.mantle.

AnatomyAnatomy

• All mollusks have a All mollusks have a full excretory full excretory system. A snail’s system. A snail’s anus is located anus is located right over it’s head right over it’s head and it poops right and it poops right onto itself. Squid onto itself. Squid and octopi excrete and octopi excrete waste out of the waste out of the mantle as they mantle as they swim.swim.

FeedingFeeding

• Radula – rough tongue or ribbon of teethRadula – rough tongue or ribbon of teeth

• Herbivores, scavengers, carnivores, Herbivores, scavengers, carnivores, omnivoresomnivores

ReproductionReproduction

• All mollusks All mollusks reproduce sexuallyreproduce sexually

• Both males and Both males and femalesfemales

HabitatHabitat

• TerrestrialTerrestrial

• MarineMarine

• FreshwaterFreshwater

• Rocky shoresRocky shores

• Niche?Niche?

• Biotic factors?Biotic factors?

• Abiotic factors?Abiotic factors?

AdaptationsAdaptations

• Cephalopods need to Cephalopods need to swim very fast so swim very fast so have closed have closed circulatory systemcirculatory system

• Bivalves have Bivalves have flattened shape and flattened shape and strong foot to hold strong foot to hold on in intertidal zoneson in intertidal zones

• Shells for defenseShells for defense

GastropodsGastropods

• Largest group of Largest group of mollusksmollusks

• ““stomach foot”stomach foot”

• 0 to 1 shell0 to 1 shell

• Movement on foot Movement on foot – slippery mucus– slippery mucus

• radularadula

BivalvesBivalves

• 2 shells held by hinge2 shells held by hinge

• No radula – filter feedersNo radula – filter feeders

• Mostly sessileMostly sessile

• Grain of sand that gets Grain of sand that gets stuck between mantle stuck between mantle and shell causes bivalve and shell causes bivalve to produce mucus – to produce mucus – pearlpearl

• Found in all water Found in all water environmentsenvironments

• OmnivoresOmnivores

CephalopodsCephalopods

• ““Head foot”Head foot”• Ocean dwellingOcean dwelling• Foot forms tentacles Foot forms tentacles

around moutharound mouth• Carnivores with radulaCarnivores with radula• Swim by jet propulsionSwim by jet propulsion• Most complex nervous Most complex nervous

system of all invertebratessystem of all invertebrates• Nautilus-external shellNautilus-external shell• Squids-small internal shellSquids-small internal shell• Octopus- no shellOctopus- no shell