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Unit 8 Invertebrates

Unit 8 Invertebrates. Ch. 27 Worms & Mollusks. What Is a Flatworm?. Flatworms are soft, flattened worms that have tissues & internal organ systems They are the simplest animals to have 3 embryonic germ layers, bilateral symmetry, & cephalization. Form & Function in Flatworms.

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Unit 8 Invertebrates

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  1. Unit 8 Invertebrates Ch. 27 Worms & Mollusks

  2. What Is a Flatworm? • Flatworms are soft, flattened worms that have tissues & internal organ systems • They are the simplest animals to have 3 embryonic germ layers, bilateral symmetry, & cephalization

  3. Form & Function in Flatworms • Parasitic worms feed on blood, tissue fluids, or pieces of cells within the host’s body • Blood flukes are parasitic flatworms that mature in the blood vessels of humans

  4. Form & Function in Flatworms • All flatworms, including this planarian, have organ systems that perform essential life functions

  5. Groups of Flatworms • The 3 main groups of flatworms are turbellarians, flukes, & tapeworms • Turbellarians are free-living flatworms • Most live in marine or fresh water

  6. Groups of Flatworms • Flukes are parasitic flatworms • Most flukes infect the internal organs of their host

  7. Groups of Flatworms • Tapeworms are long, flat, parasitic worms that are adapted to life inside the intestines of their hosts

  8. What Is a Roundworm? • Most roundworms are free-living, inhabiting soil, salt flats, aquatic sediments, & water, from polar regions to the tropics • Many others are parasitic & live in hosts that include almost every kind of plant & animal

  9. What Is a Roundworm? • Roundworms are unsegmented worms that have 2 openings, a mouth & an anus

  10. Roundworms & Human Disease • Parasitic roundworms include trichinosis-causing worms, filarial worms, ascarid worms, & hookworms • Trichinosis-causing worms reproduce in the intestines of their host & then form cysts in their muscle tissue

  11. Roundworms & Human Disease • Filarial worms are found mainly in the tropics • They are transmitted from 1 host to another through biting insects • Ex.) Elephantiasis

  12. Roundworms & Human Disease • Ascarid worms absorb the host’s digested food & can cause severe malnutrition • Blockage of the intestine can be so severe that it can cause death

  13. What Is an Annelid? • Annelids are worms with segmented bodies • They are also called segmented worms because the body is divided into many similar segments

  14. Form & Function in Annelids • Feather-duster worms exchange gases underwater using feathery gills

  15. Form & Function in Annelids • Some annelids, including earthworms, are hermaphrodites - each worm produces both egg & sperm • During mating, the worms exchange sperm, which will be used to fertilize egg cells

  16. Earthworm

  17. Groups of Annelids • There are 3 main classes: oligochaetes, leeches, & polychaetes • Oligochaetes have few setae, & live in soil or fresh water

  18. Groups of Annelids • Leeches are typically external parasites that suck the blood & bloody fluids of their host

  19. Groups of Annelids • Polychaetes are marine annelids have paired, paddlelike appendages tipped with setae • Ex.) Fireworm

  20. Ecology of Annelids • Most annelids spend their lives burrowing through soil, aerating it, & mixing it • Their tunnels provide passageways for plant roots & water, & allow the growth of beneficial oxygen-requiring soil bacteria

  21. What Is a Mollusk? • Mollusks are soft-bodied animals that usually have an internal or external shell

  22. Form & Function in Mollusks • The body plan of most mollusks includes a foot, mantle, shell, & visceral mass

  23. Form & Function in Mollusks • Mollusks have evolved a variety of ways of responding to potential danger • Snails withdraw into their shells • Octopi & squids squirt ink from their digestive tracts, causing temporary numbness of predators

  24. Groups of Mollusks • The 3 major classes of mollusks are gastropods, bivalves, & cephalopods • Gastropods are shell-less or single-shelled mollusks that move by using a muscular foot

  25. Groups of Mollusks • Members of the class Bivalvia have 2 shells that are held together by 1 or 2 powerful muscles • Includes: clams, mussels, oysters, & scallops

  26. Groups of Mollusks • Cephalopods are typically soft-bodied mollusks in which the head is attached to a single foot • The foot is divided into tentacles or arms • Nautiluses are the most primitive group of cephalopods

  27. Groups of Mollusks • Cephalopods have the most complex nervous system of all the mollusks, with a highly developed brain & sense organs, like the eye of a squid

  28. Ecology of Mollusks • Mollusks are important source of food for many organisms, including humans

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