Post on 18-Feb-2021
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Dissection of the Clam
Venus mercenaria
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Taxonomy of Bivalve Mollusks
Kingdom
Phylum
Class
Genus
Species
• Animalia
• Mollusca
• Bivalvia
• Venus
• mercenaria
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Bivalve 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 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 clamsare smaller (3/4 inch) and typically more round
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Indirect Development
• Goes through a free-swimming, larval stage called the trochophore
• Adults move slowly by their extendable foot
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Bivalve Mollusks• Protostomes – blastopore becomes the mouth
• Have a fully lined body or mantle cavity
• Body organs called visceral massprotected by mantle which secretes the shell
• Open circulation• Most are sessile or sedentary• Includes clams, oysters, scallops, & mussels
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Bivalves
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External Anatomy
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Bivalve 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 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 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 ligamentholds the two halves of the shell together
Bivalve Shell
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Internal Anatomy
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Scissor tips or a screwdriver & can be used to open the shell
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Adductor 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) shell
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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 Flow• Incurrent siphons aid in bringing in water
with food and oxygen
• Cilia direct water into the gills, while labialpalps 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 System
• Consists of 3 pairs of ganglia (brain)
• Has 2 pairs of nerve cordsextending 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 removed by excurrent Siphon:
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