[PPT]Clam Dissection · Web viewDissection of the Clam Venus mercenaria * copyright...

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Dissection of the Clam

Venus mercenaria

copyright cmassengale

Taxonomy of Bivalve Taxonomy of Bivalve MollusksMollusks

KingdomPhylumClassGenus Species

•Animalia•Mollusca•Bivalvia•Venus•mercenaria

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

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

Indirect DevelopmentIndirect Development• Goes through

a free-swimming, larval stage called the trochophore

• Adults move slowly by their extendable foot

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, & musselscopyright cmassengale

BivalvesBivalves

9copyright cmassengale

External AnatomyExternal Anatomy

Bivalve ShellBivalve Shell• Umbo is the raised, oldest part of the

shell and is used to find surfaces

Dorsal

Ventral

Bivalve ShellBivalve Shell• Shell show regular spacing of external growth rings on

shells and their progressive crowding as the animals grow older

Growth Rings

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

•The hinge ligament holds the two halves of the shell together

Bivalve ShellBivalve Shell

Internal AnatomyInternal Anatomy

Scissor tips or a screwdriver & can be used to open the shell

Adductor MusclesAdductor Muscles

Strong adductor muscles help open & close the valves and must be cut to examine the interior of the clam

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”

Teeth located on the dorsal edge of the shell lock to keep shells from sliding

The mantle makes a CaCO3 (limestone) shellcopyright cmassengale

Mantle cavity

Gills hang outside visceral mass (body) in the mantle cavity & remove O2 as H2O flows over them

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

VISCERAL MASS -contains respiratory, digestive, & reproductive

systems

HEART & PERICARDIAL CAVITY

Nervous SystemNervous System

•Consists of 3 pairs of ganglia (brain)

•Has 2 pairs of nerve cords extending from this

•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:

Resourcehttp://www.biologyjunction.com/pwpt_biology.htm

[PPT]Clam Dissection · Web viewDissection of the Clam Venus mercenaria * copyright...

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