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Phylum Mollusca

Phylum Mollusca. Characteristics. Soft body Usually have an internal or external shell Bilateral symmetry Word mollusca means “soft” More complex organ system Coelomates Muscular No skeleton. Body Plan. Many different shapes Most have 4 main parts Foot: usually for movement

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Phylum Mollusca

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  1. Phylum Mollusca

  2. Characteristics • Soft body • Usually have an internal or external shell • Bilateral symmetry • Word mollusca means “soft” • More complex organ system • Coelomates • Muscular • No skeleton

  3. Body Plan • Many different shapes • Most have 4 main parts • Foot: usually for movement • Mantle: thin layer of tissue that covers body • Shell: calcium carbonate • Visceral mass: beneath the mantle; consists of internal organs

  4. Feeding • Radula – rough tongue or ribbon of teeth • Herbivores, scavengers, carnivores, omnivores

  5. Respiration • Aquatic- Breath using gills inside their mantle cavity • Land-mantle cavity lined with blood vessels • Must be kept moist for diffusion

  6. Circulation • Either closed or open circulatory system • Open-simple heart • Octopi and squid-closed (no heart like earthworm) • Snails and slugs- open

  7. Excretion • All mollusks have a full excretory system. • Cells called nephridia remove ammonia from blood and release it outside the body. • One way digestive system – mouth to anus • Squid have a tube-like structure called a siphon through which water enters and leaves

  8. Response • Snails, clams, etc have a simple nervous system • Few ganglia and nerve cords near mouth • Simple sense organs • Chemical receptors • Eye spots

  9. Response • Cephalopods like Octopi have a complex nervous system • Most complex of the invertebrates • Well developed brain • Can be trained!

  10. Reproduction • All mollusks reproduce sexually • Some are dioecious • External fertilization • Some are monoecious

  11. Habitat • Terrestrial • Marine • Freshwater • Rocky shores

  12. Classes • Class Gastropoda – snails, slugs • Class Cephalopoda – octopus, squid, nautilus • Class Bivalvia – oysters, clams

  13. Gastropods • Largest group of mollusks • “stomach foot” • 0 to 1 shell • Movement on foot – slippery mucus • radula

  14. Bivalves • 2 shells held by hinge • No radula – filter feeders • Mostly sessile • Grain of sand that gets stuck between mantle and shell causes bivalve to produce mucus – pearl • Found in all water environments • Omnivores

  15. Cephalopods • “Head foot” • Ocean dwelling • Foot forms tentacles around mouth (8 or more) • Carnivores with radula • Swim by jet propulsion • Nautilus-external shell • Squids-small internal shell • Called a Penn • Octopus- no shell

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