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Mollusks and Segmented Worms

Mollusks and Segmented Worms. Chapter 15.2. Mollusks. Soft-bodied invertebrates Bilateral symmetry Usually one or two shells Organs are in a fluid filled cavity Snails, clams, squids. Body Plan. All have a mantle – thin layer of tissue that covers the body organs

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Mollusks and Segmented Worms

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  1. Mollusks and Segmented Worms Chapter 15.2

  2. Mollusks • Soft-bodied invertebrates • Bilateral symmetry • Usually one or two shells • Organs are in a fluid filled cavity • Snails, clams, squids

  3. Body Plan • All have a mantle – thin layer of tissue that covers the body organs • Secretes the shell or protects the body • Mantle cavity contains gills

  4. Body Plan • Open circulatory system – blood moves from heart to vessels to open spaces around organs • On the underside is the foot

  5. Gastropods • Snails, conchs, abalones, whelks, sea slugs, garden slugs • Single shell • Pair of tentacles with eyes • Radula – tongue-like organ with rows of teeth • Slugs protected by mucus

  6. Bivalves • Clams, oysters, and scallops • Hinged, two-part shell • Close shell by contracting strong muscles • Attach to surfaces with a strong thread or cement • Burrow with their foot

  7. Cephalopods • Squids, octopuses, cuttlefish, nautiluses • Large, well-developed head • Foot divided into tentacles with suction cups • All are predators • Well-developed nervous system • Eyes like humans • Closed circulatory system – series of closed vessels • Cephalopod video

  8. Segmented Worms • Earthworms, marine worms and leeches • Called annelids – means little rings • Setae – bristle-like structures • Used hold onto and move through soil • Bilateral symmetry • A body cavity that hold organs • Two body openings

  9. Earthworm Body Systems • Anterior and posterior ends • Segments each have for pairs of setae • Move using two sets of muscles

  10. Digestion and Excretion • Takes in soil through its mouth • Stores food in the crop • Gizzard grinds the soil and organic matter • Passes to intestines where nutrients are absorbed • Waste passes through anus • Leave behind castings

  11. Circulation and Respiration • Closed circulatory system • Two blood vessels (ventral and dorsal) • Aortic arches pump blood • Exchange carbon dioxide and oxygen through their skin

  12. Nerve Response and Reproduction • Small brain in first segment • Nerve cord connects to brain • Hermaphrodites • Cannot fertilize its own eggs • Must reproduce sexually

  13. Marine Worms • Polychaetes • Setae occur in bundles

  14. Leeches • Don’t have setae • Feed on blood of other organisms • Produce an anesthetic • Can eat aquatic insects if necessary • Are used in medicine

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