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

Modified from :http://www.biologyjunction.com

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Internal AnatomyInternal Anatomy

Modified from :http://www.biologyjunction.com

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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

Modified from :http://www.biologyjunction.com

12Modified from :http://www.biologyjunction.com

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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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14Modified from :http://www.biologyjunction.com

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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

Modified from :http://www.biologyjunction.com

18Modified from :http://www.biologyjunction.com

19Modified 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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