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Bivalves are a group of specialized filter feeders including clams, oysters, mussels, scallops, and shipworms. These animals are characterized by their compressed body within the mantle cavity enclosed by two hinged shells (valves). Unlike other mollusks, bivalves lack a radula and rather feed by filtering water through their gills and trapping small particles to eat.
Clams burrow into sediment by utilizing their muscular foot. Mussels and scallops attach themselves to hard substrates by using byssal threads, giving them the ability to stay anchored against strong currents. However, scallops utilized their two valves to propel themselves through open waters, making them both benthic and nekton organisms. Shipworms have hardly retained the same shell as other groups of bivalves but still has about 10% around its head. This allows the animal to bore into and feed upon wood, digesting the wood fibers with cellulase ezyme.
Defining Chacteristics
Defining Chacteristics
Two hinged shells (valves)
Encloses the mantle cavity and holds the bivalve's compressed body plan
Bilateral symmetry
No radula- feed via filtering food items with their gills or siphon
Triploblastic body plan: endoderm, mesoderm, ectoderm
Head present
Muscular foot used for burrowing, crawling, or anchoring to surfaces
Most species are slow moving
Scallops utilize their valves to propel themselves through open waters
Byssal threads used by certain species to adhere themselves to hard surfaces
Complete digestive tract: separate openings for mouth and anus that allows for maximized digestive efficiency
Open circulatory system
Simple nervous system
Reproductive adaptations
Reproductive adaptations
Sexes usually separate (dioecious), some species are hermaphroditic
Fertilization typically external with both eggs and sperm released into the water
Egg stage: fertilized eggs devlelop into trochophore larva
Trochophore larva: Tiny, ciliated larval stage that feeds on plankton
Veliger larva: Larva develops a small shell and ciliated velum for swimming and feeding
Metamorphosis: Larva attach or burrow into substrate before transforming into juvenile bivalves
Adult stage: Reproductive system fully developed with the capability of mating
Some species may skip free-swimming larval stages or develop inside their mother
Where are they found?
Where are they found?
Clams burrow into benthic substrates
Range from shallow coastal waters to deep ocean
Oysters and mussels attach to hard surfaces
Sometimes attach to other individuals of the same species
Typically found at depths from 1 to 10 meters
Scallops are considered nekton animals and swimming freely through open waters
Shipworms found burrowing into and feeding upon wood
Driftwood
Wooden docks
Dock pilings
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