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• Unsegmented soft body• Mollusks have 3 main parts -visceral mass, modified foot, & mantle
• Mollusks have a visceral mass (contains the organs)• Mollusks have a Modified Foot
– Muscular foot and/or tentacles• Have a mantle (fold that wraps around visceral mass
& secretes the shell) • Most have shell (internal or external)
– Or remnants of a shell• Pen in squid
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• Body Cavity- true coelom
• Symmetry- bilateral
• Organ systems-
-have organs for circulation, respiration, digestion, excretion, & nervous system
• Respiration- most gills (some snails have simple lung)
• Circulation- 3 chambered heart- most have open circulatory system (but squids & octopuses have closed circ. system)
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• Digestion- one way digestive system: separate mouth and anus
• Reproduction- most are separate sexes and reproduce sexually by doing external fertilization (except for snails which are hermaphrodites)
• Nervous- brain, eyes, and nerves
• Excretion- nephridia remove liquid wastes and anus removes solid waste
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Tentacles/ modified foot head Mantle
cavityShellfootMantle
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Classes of MollusksThere are 7 classes of mollusks but this course will look at the 3 main classes.
• Class Cephalopoda –
octopus and squid
• Class Gastropoda –
slugs and snails
• Class Bivalvia – clams,
mussels, scallops
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Class Gastropoda
• Types- snails, conches, limpets free-living; marine, terrestrial, fresh water• noticeable head• single shell, often spiral• muscular foot secretes mucus to form a slimy path to glide along• Feeding-most herbivores that scrape algae off rocks with radula• Mantle- secretes shell
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Snail Anatomy
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Class Bivalvia• Types- clams, scallops, oysters• marine and freshwater• gill used for gas exchange• all are sessile, filter feeders and filter food
from the water• all have two part shells(bivalves)-Muscular foot- used to dig into sand
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Class Cephalopoda•Types- octopus, squid,
cuttlefish • Exclusively marine• Shell- “pen”- internal
remnant of a shell• Use fins and siphon to
move (jet propulsion)• Modified foot= tentacles• Fast swimming predators
-use tentacles to catch prey• Use a beak-like jaw (radula)
to eat prey• Have a special camera like
eye
Ex- Giant Squid
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Squid External Anatomy
Siphon
Fins
Mantle
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Squid Internal Anatomy
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