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Phylum Platyhelminthes (Chapter 27-1)

Phylum Platyhelminthes (Chapter 27-1). Please set up your notebook for Cornell Notes. Flatworms Characteristics Soft, flattened worms w/tissue and internal organ systems Simplest animal w/bilateral symmetry, three germ layers and cephalization

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Phylum Platyhelminthes (Chapter 27-1)

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  1. Phylum Platyhelminthes (Chapter 27-1) Please set up your notebook for Cornell Notes

  2. Flatworms • Characteristics • Soft, flattened worms w/tissue and internal organ systems • Simplest animal w/bilateral symmetry, three germ layers and cephalization • Bilateral symmetry allows for more rapid movement than radially symmetrical animals • Acoelomate  no body cavity

  3. Form and Function • Feeding • Carnivores, scavengers, or parasites • Have single opening to digestive cavity (mouth/anus) • Pharynx  muscular tube near mouth that pumps food directly into the digestive cavity (gut) • Food is digested by cells in digestive cavity and nutrients distributed by diffusion • Parasitic flatworms get nutrients from host’s blood

  4. Respiration, Circulation and Excretion • Because flatworms are so thin, most don’t need a circulatory system • They can rely on diffusion to transport oxygen, nutrients and to get rid of wastes • Specialized cells • Some flatworms have flame cells  remove excess water from the body through pores in skin • May also filter and remove wastes

  5. Response • Ganglia  groups of nerve cells in head region that control nervous system • Two long nerve cords that run length of the body • Shorter nerve cores run across body • Have eyespots near the anterior end • Can detect changes in light • Also have cells that can detect changes in environment

  6. Movement • 2 ways • Cilia to glide through the water • Muscle cells to twist and turn • Reproduction • Free living flatworms are hermaphrodites  have both male and female reproductive structures • Pair up and exchange sperm • Free living flatworms also reproduce asexually by fission  splitting into two identical organisms • Parasitic flatworms have complex cycles with both asexual and sexual parts

  7. Classes of Platyhelminthes • Class Turbellaria • Planarians • Free living in fresh or marine water • Bottom dwellers

  8. Class Trematoda • Flukes • Parasitic  infect organs of host • Can have multiple hosts

  9. Class Cestoda • Tapeworms • Long, flat parasitic worms that live in the intestines of their hosts • Have no digestive tract • Structures • Scolex head, contains suckers or hooks • Used to attach to the intestine wall • Proglottids the segments that make up the body • Mature proglottids have both male and female structures

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