The bivalves

The BivalvesPhylum Mollusca

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Anatomy• Two shells (valves)

held together tightly by adductor muscles

• No head, brain is a set of nerve cells (ganglia)

• Gills to take oxygen from water

• Mantle secretes the shell

• Bilateral symmetry

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Class Bivalvia – The Bivalves(clams, mussesls, scallops, oysters)

Habitat• Benthic– Most Sessile, few motile– Infauna – most burrow

down– Epifauna – some live on

seafloor• Mussels attach with

byssal threads• Scallops swim by

clapping shells together

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Feeding-Most are planktivores-Incurrent & excurrent Siphons-Important filter feeders-up to 25 gallons of water/day

Bivalve Reproduction

-Separate sexes-External fertilization and development

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Pearl Formation• Mostly in oysters• Protection against

parasites or grains of sand

• Often not round• Natural pearls are

more costly• Cultured pearls are

made by inserting an object in the oyster

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Clam Internal Anatomy

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The bivalves

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