Bivalvia Flashcards
(29 cards)
What are the characteristics of Bivalvia?
- Laterally compressed body
- Bivalve shell with a dorsal hinge
- Spacious lateral mantle cavities
- Minimal cephalization
- NO radula
How is water circulated?
External water circulated thru the mantle cavity
-in the inhalant siphon and out the exhalant siphon
How is the foot modified in Bivalvia?
Flattened, modified for burrowing
What holds the shell valves together?
What open/close the shell valves?
Hinge ligament
Close: Anterior/Posterior adductor muscles
Open: hinge ligament (also re-extends muscles)
How does the hinge ligament open the shell valves?
It is deformed by the muscles contracting. When that energy is released, it springs back to its original shape
How do Bivalves burrow?
a)
1. Shell adductor muscles relax, shells gape open to anchor shell
2. Foot laterally compressed, pushes into substrate
b)
3. Expansion of foot terminus (anchor)
4. Contraction of adductor muscles (closes shell)
5. Contraction of shell-attached dorso-ventral muscles pulls clam down
Where are the shell-attached dorso-ventral muscles found?
In the foot
What are the inner, middle and outer lobes in bivalves specialized for?
Inner: muscle
Middle: sensory (photoreceptors)
Outer: shell secretion
What is the shell covered by?
A layer of proteinaceous periostracum
What is the shell secreted by?
The mantle
Where are sensory structures found? What are some examples?
at the mantle margin
eg: tentacles, eyespots
Identify the features of an empty shell
- pallial line
- pallial sinus
- anterior/posterior adductor muscle scars
- teeth (at hinge)
- hinge ligament
What are the 2 subgroups?
Protobranchia
Autobranchia
How is autobranchia subdivided?
Pteriomorpha (mussels, oysters)
Heteroconchia (most extant bivalves)
How do PROTOBRANCHIA feed?
-deposit feeding using palp tentacles
How do PROTOBRANCHIA do gas exchange?
-siphons and gills (ctenidia)
What are the roles of autobranch ctenidia? What is the name of these ctenidia?
Gas exchange AND suspension feeding
Lamellibranch Ctenidia
What are the two parts of the ctenidia?
Outer demibranch (near shell) Inner demibranch
What are the 3 types of ctenidia, what do they do?
- Lateral cilia: create water current
- laterofrontal cilia: intercept particles
- frontal cilia: carry particles down filament
How are the particles carried to the mouth?
Once they reach the elbow of the ctenidia, they are carried to the mouth.
How do heterochochs prevent sand coming into their shells?
Fusion of mantle folds except foot and siphon
How do septibranchs feed?
are predators
-INHALANT SIPHON creates suction to suck prey into siphon and into mantle cavity
How do spetibranchs create that suction?
- closes shell valves
- septum elevated, this expands internal volume of mantle cavity, this sucks in prey item at exterior opening of siphon
How can you tell the burrowing depth of a species?
The length of its siphons,
