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Chapter 27.1 Flatworms, the Simplest U nsegmented Worms

Chapter 27.1 Flatworms, the Simplest U nsegmented Worms. Hannah Reagan 3 rd period. Introduction . Phylum Platelminhes

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Chapter 27.1 Flatworms, the Simplest U nsegmented Worms

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  1. Chapter 27.1Flatworms, the Simplest Unsegmented Worms Hannah Reagan 3rd period

  2. Introduction • Phylum Platelminhes • Flatworms are soft, flattened worms that have tissues and internal organ systems. They are the simplest animals to have three embryonic germ layers, bilateral symmetry, and cephalization. • (Cephalization means the concentration of sense organs and nerve cells at the front of an animal’s body)

  3. Flatworms in General • Acoelomates, which means “without coelom” • Bilateral • Aquatic • Incomplete digestive tract • Diffusion instead of Excretion, Circulatory, and Respiratory systems • Reproduce sexually and asexually • Ganglia

  4. Feeding Free-Living Parasitic • carnivores or scavengers • Flatworms have a pharynx-muscular tube at the end of the throat that connects the mouth with the rest of the digestive tract and serves as a passageway for air and food • Digested food is diffused from the digestive cavity to other body tissues • feed on blood, tissue fluids, or pieces of cells within their host’s body • Some have pharynx • Absorb nutrients from the host’s digested food

  5. Respiration, Circulation, Excretion • Just diffusion • Flame cells-specialized cells that remove excess water from body, function in excretion

  6. Response and Movement • Several ganglia-groups of nerve cells that control the nervous system, little brains • Nerve cords form a ladder • Parasitic flatworms do not always have such a complex nervous system • Eyespot-group of cells that detect changes in amount of light in environment, looks like an eye • Move by cilia and muscle cells

  7. Reproduction • Most free-living are hermaphrodites (individual that has both male and female reproductive organs) and reproduce sexually • Also free-living can go through asexual reproduction by fission (organism splits in two, and each half grows new parts to become a complete organism • Parasitic flatworms have complex life cycles that usually go through both sexual and asexual reproduction

  8. Groups 1.Turbellarians 3.Tapeworms 2.Flukes

  9. Turbellarians • Class Turbellaria • free-living • Marine or fresh water • bottom dwellers • Vary in color, form, and size Look! They’re cross-eyed!

  10. Flukes • Class Trematoda • Parasitic • Infect internal organs of their host • Primary host is a human • Cause schistosomiasis

  11. Tapeworms • Class Cestoda • Long, flat, parasitic • Infect intestines of their host • No digestive tract • Scolex-the head, contains suckers or hooks • Proglottids- segments that make up the worm’s body • Testes-male reproductive organs • Contain both male and female reproductive organs

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