Post on 12-Mar-2018
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Dissection of the Clam
Venus mercenaria
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Taxonomy of Bivalve Taxonomy of Bivalve MollusksMollusks
KingdomPhylumClassGenus Species
•Animalia•Mollusca•Bivalvia•Venus•mercenaria
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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 sexes
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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
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Indirect DevelopmentIndirect Development• Goes through
a free-swimming, larval stage called the trochophore
• Adults move slowly by their extendable foot
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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,
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BivalvesBivalves
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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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Scissor tips or a screwdriver & can be used to open the shell
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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) shellcopyright cmassengale
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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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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
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VISCERAL MASS -contains respiratory, digestive, & reproductive
systems
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HEART & PERICARDIAL CAVITY
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Nervous SystemNervous System
•Consists of 3 pairs of ganglia (brain)
•Has 2 pairs of nerve cords extending from this
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•Nitrogen waste from kidney• Digestive waste from anus• Sperm or egg (if external fertilization) • Larva (if internal fertilization)
Released into Mantle Cavity to be Released into Mantle Cavity to be removed by excurrent Siphon:removed by excurrent Siphon:
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Resourcehttp://www.biologyjunction.com/pwpt_biology.htm