PHYLUM MOLLUSCA

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PHYLUM MOLLUSCA

• COMMONLY CALLED SHELLFISH
• SECOND LARGEST ANIMAL POPULATION

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MOLLUSKS

• FREE-LIVING
• MARINE, TERRESTRIAL,FRESHWATER
• HAVE A 3 PART BODY
• FOOT - LOCOMOTION
• VISCERAL MASS INTERNAL ORGANS
• MANTLE SECRETES SHELL

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MOLLUSKS

• 4 MAJOR CLASSES BASED UPON
• FOOT TYPE
• SHELL TYPE
• POLYPLACOPHORA
• GASTROPODS
• CEPHALOPODS
• BIVALVES

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MOLLUSKS

• 3 GERM LAYERS
• BILATERAL SYMMETRY
• ORGAN SYSTEM LEVEL
• NEPHRIDIA TUBULES FOR EXCRETION
• RESPIRATION INVOLVES GILLS OR MANTLE LUNG AIR
  POCKETS
• REPRODUCTION
• HERMAPHRODITIC
• SEPARATE SEXES

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MOLLUSKS

• POLYPLACOPHORA
• SHELL IN PIECES ON DORSAL SURFACE
• FLAT, CREEPING VENTRAL FOOT
• DATE BACK TO PREHISTORIC TIMES
• HABITAT - ROCKY MARINE SHORES
• EXAMPLE CHITON

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MOLLUSKS

• GASTROPODS
• FLAT, CREEPING BELLY FOOT
• UNIVALVED COILED SHELL IF PRESENT
• BODY SYMMETRY HAS TORSION OF VISCERAL MASS
• HEAD WITH EYE STALKS
• VARIOUS NUTRITIONAL MODES
• MOST AQUATIC, SOME TERRESTRIAL
• EXAMPLES SNAILS, SLUGS

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Figure 25.18Page 426
Body Plan of a Snail
anus
gill
mantle cavity
excretory organ
heart
digestive gland
shell
stomach
mantle
radula
foot
Do not post photo to Internet
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Figure 25.20bPage 428
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Figure 25.20bPage 428
BEFORE TORSION
AFTER TORSION
mouth
mouth
anus
edge of mantle
anus, which discharges into mantle cavity
foot
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MOLLUSKS

• CEPHALOPODS
• TENTACLES - ARM LIKE FOOT
• FEET LOCATED ON HEAD
• SHELL REDUCED TO INSIDE OR ABSENT
• CLOSED CIRCULATION
• WELL DEVELOPED NERVOUS SYSTEM
• BEAK LIKE JAWS
• MARINE PREDATORS
• INK SAC
• JET PROPULSION
• MARINE

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Figure 25.22Page 429
Body Plan of a Cuttlefish
esophagus
stomach
kidney
digestive gland
brain
arm
jaw
mantle
reproductive organ
internal shell
siphon
ink sac
heart
accessory heart
tentacle
radula
anus
gill
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MOLLUSKS

• BIVALVES
• BIVALVED SHELL W/ HINGE AND UMBO
• ADDUCTOR MUSCLES CONTROL SHELL
• HATCHET FOOT FOR BURROWING
• INTERNAL / EXTERNAL SIPHONS
• FILTER FEEDERS PLANKTON
• TUBE TYPE GUT WITH TORSION
• OPEN CIRCULATION
• AQUATIC
• GILLS

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Figure 25.21Page 429
mouth
retractor muscle
left mantle
retractor muscle
water flows out through exhalant siphon
water flows in through inhalant siphon
foot
palps
left gill
shell
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MOLLUSKS

• EVOLUTIONARY MILESTONE
• TRUE COELOM