dissection of the clam - imater · 2020. 3. 16. · dissection of the clam venus mercenaria...

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Dissection of the Clam

Venus mercenaria

copyright cmassengale

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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


9copyright cmassengale

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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:


dissection of the clam - imater · 2020. 3. 16. · dissection of the clam venus mercenaria...

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