Mollusca: Bivalvia

Question 1

Characteristics (5)

Answer 1

Laterally compressed body 
Bivalve shell - dorsal hinge 
Spacious lateral mantle cavities 
Minimal cephalization
NO radula

Question 2

Shell Closing/Opening Action

Answer 2

The anterior and posterior abductor muscles contract (shorten) and this closes the shell
The hinge ligament provides the antagonist for the muscle
Inner ligament is compressed, outer ligament is stretched
Once contraction stops the ligaments spring the shell back open

Question 3

Burrowing Action (5)

Answer 3

Shell adductor muscles relax, shell gape open (anchor)
Foot laterally compressed, pushes foot into substrate
Expansion of foot terminus (anchor)
Contraction of adductor muscle
Contraction of dorso-ventral muscle

Question 4

Shell secretion mechanism

Answer 4

Occurs via the outer lobe
First excretes a protein layer outside (periostracum)
Then fills in the gap with CaC03 secretions

Question 5

Feeding diversity (3)

Answer 5

Protobranchia: Deposit feed using palp tentacles
Their gills are only for gas exchange

Autobranchia: They are filter-feeders
Use ctenidia for gas exchange and feeding
Lateral cilia create water current, laterofrontal cilia intercept particles and frontal cilia carry particles down filament

Septibranchia: predators via suction feeding
Muscular, perforated diaphragm for suction feeding

Question 6

Habitat diversity

Answer 6

Shallow burrowers (cockles)
Deep burrowers (geoduck) -- very long siphons 
Surface dwelling (mussels) -- byssal threads hold them fast to the rocks 
Boring bivalves (shipworms)