1 dissection of the clam venus mercenaria modified from ::
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Dissection of the Clam
Venus mercenaria
Modified from :http://www.biologyjunction.com
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Bivalve MollusksBivalve Mollusks
•Soft bodies invertebrates•Have a muscular foot that
can be extended for movement
•Two part, hinged shell•Complete, one-way
digestive tract with a mouth & anus
•Separate sexesModified from :http://www.biologyjunction.com
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Bivalve MollusksBivalve Mollusks• No eyes or distinct
head• Have siphons to
circulate water through their bodies
• Filter feed on plankton
• Mussels are large and have a flat, more oblong shell shape, while freshwater clams are smaller (3/4 inch) and typically more round
Modified from :http://www.biologyjunction.com
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Bivalve MollusksBivalve Mollusks• Protostomes – blastopore
becomes the mouth• Have a fully lined body or
mantle cavity• Body organs called visceral
mass protected by mantle which secretes the shell
• Open circulation• Most are sessile or sedentary• Includes clams, oysters,
scallops, & musselsModified from :http://www.biologyjunction.com
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External AnatomyExternal Anatomy
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Bivalve ShellBivalve Shell• Umbo is the raised, oldest part of the
shell and is used to find surfaces
Dorsal
Ventral
Anterior
Posterior
UMBO
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Bivalve ShellBivalve Shell• Shell show regular spacing of external growth rings
on shells and their progressive crowding as the animals grow older
Growth Rings
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Bivalve ShellBivalve Shell• Bivalves have an incurrent and excurrent siphon to bring
in water containing food & O2 and for excess water & wastes to leave
Siphons
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•The hinge ligament holds the two halves of the shell together
Bivalve ShellBivalve Shell
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Internal AnatomyInternal Anatomy
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Adductor MusclesAdductor Muscles
Strong adductor muscles help open & close the valves and must be cut to examine the interior of the clam
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Inside Shell Lining
• The inside of the shell is pearly and smooth to protect the body
• Oysters coat irritants with a substance called “mother of pearl”
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Teeth located on the dorsal edge of the shell lock to keep shells from sliding
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The mantle makes a CaCO3 (limestone) shellModified from
:http://www.biologyjunction.com
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Mantle cavity
Gills hang outside visceral mass (body) in the mantle cavity & remove O2 as H2O flows over them
Gills
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18Modified from :http://www.biologyjunction.com
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Water FlowWater Flow• Incurrent siphons aid in bringing in
water with food and oxygen• Cilia direct water into the gills, while
labial palps direct water into the mouth
Cilia on the gills pulls in water
move food toward the mouth
Modified from :http://www.biologyjunction.com
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