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PLATYHELMINTHES

PLATYHELMINTHES. Eumetazoa: Bilateria: Phylum Platyhelminthes (flatworms) marine, freshwater, terrestrial. PLATYHELMINTHES. either Protostomia or Lophotrochozoa triploblastic: 3 germ layers ectoderm: epidermis, nervous tissue mesoderm: true muscle tissue

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PLATYHELMINTHES

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  1. PLATYHELMINTHES • Eumetazoa: Bilateria: Phylum Platyhelminthes (flatworms) • marine, freshwater, terrestrial

  2. PLATYHELMINTHES • either Protostomia or Lophotrochozoa • triploblastic: 3 germ layers • ectoderm: epidermis, nervous tissue • mesoderm: true muscle tissue • endoderm: gastrodermis lining gastrovascular cavity • acoelomate

  3. PLATYHELMINTHES • lack some organ systems (circulatory, respiratory) • diffusion: reason why small and flat • have others (muscular, nervous, digestive, excretory, reproductive) • nervous system (Fig. 49.2): eye spots, rudimentary brain, nerve cords • cephalization (head); Fig. 33.10, Fig. S4-2

  4. PLATYHELMINTHES • hermaphroditic: male and female reprod. systems in same individual • adaptive advantage: every individual potential mate • digestive system: mouth, pharynx, gastrovascular cavity • one way gut; no anus • invagination: increases surface area

  5. PLATYHELMINTHES • excretory system: protonephridia (Fig. 44.11); proto = first, nephrus = kidney • branching network of tubules • flame-bulb cell with cilia draws mostly water, some waste into tubules • exit via nephridiopores

  6. PLATYHELMINTHES • free-living (non-parasitic) ancestral life history • many parasitic in vertebrate gut • suckers/hooks; Fig. S4-3 • reduce/lose some ancestral characters • tapeworms: no mouth/gastrovascular cavity/excretory structures; diffusion • mostly reproductive organs • Fig. 33.12

  7. MALFORMED FROGS • mystery of the malformed frogs • August 1995: school kids in MN, field trip to a pond; amphibian malformation

  8. MALFORMED FROGS • most states, range of deformities • hypothesis: endocrine disrupting chemicals • disrupt development by disrupting hormones

  9. MALFORMED FROGS • alternative: trematode hypothesis • trematodes (= flukes) • Ribeiroia life cycle: encysts in limb buds

  10. MALFORMED FROGS • can cause deformities, but why now? • human-caused ecosystem disruption • nutrient runoff: organic pollution (fertilizer, manure, sewage) • increased snail population (a key host) • modified hypothesis: nutrient-trematode

  11. NEMATODA • Eumetazoa: Bilateria: Phylum Nematoda (roundworms)

  12. NEMATODA • Protostomia or Ecdysozoa • pseudocoelom • complete digestive tract (2 openings) hangs free in pseudocoelom; Fig. S5-1 • cylindrical, unsegmented body • cuticle: tough, thick outermost layer around epidermis; ecdysis

  13. NEMATODA • hydrostatic skeleton: fluid in pseudocoelom; high pressure • nervous system: anterior nerve ring, dorsal/ventral nerve cords • no circulatory/respiratory systems; diffusion • muscular system: longitudinal muscle • locomotion: contraction; thrashing

  14. NEMATODA • only sexual reproduction (Fig. S5-2) • some hermaphroditic, others dioecious • dioecious: separate male, female • reprod. system fills most of organism

  15. NEMATODA • free-living (soil); parasitic • uniform structurally, diverse ecologically • species differ in specific habitat • probably over one million species: speciose • 1 sq m of marine mud: 4.5 million individuals!; very successful • much to be learned

  16. NEMATODA • Caenorhabditis elegans (C. elegans) • model organism • free-living soil nematode; easy to raise • transparent; life cycle: 3½ days • every cell mapped, fate known; Fig. 47.22

  17. C. elegans • entire genetic sequence known • huge medical applications • humans, nematodes both bilaterians • evolutionary medicine: studying other organisms for insight into humans

  18. ANNELIDA • Eumetazoa: Bilateria: Phylum Annelida (segmented worms) • Protostomia or Lophotrochozoa • coelomate • segmentation: repeated muscular, nervous, excretory elements divided by septae • annelida = little rings • Fig. 33.22

  19. ANNELIDA • hydrostatic skeleton: fluid in coelom • circulatory system: closed; Fig. S6-3 • heart: muscular blood vessels • dorsal, ventral blood vessel; Fig. S6-1 • capillaries: small branches of blood vessels

  20. ANNELIDA • excretory system: metanephridia (Fig. 44.12) • fluid enters nephrostome, passes through coiled tubule • useful nutrients return to circ. system, wastes excreted via nephridiopore

  21. ANNELIDA • nervous system: ventral nerve cord with ganglia (swellings); brain • muscular system: longitudinal and circular muscles • locomotion: muscular contraction works against hydrostatic skeleton of coelom • setae (bristles) • digestive system: subdivided and more specialized • hermaphroditic or dioecious

  22. ANNELIDA • leeches • specialized as predators or blood feeders • don’t confuse with trematode • no obvious head; no septae or setae • suckers for temporary attachment • large digestive system for blood • secrete hirudin: anticoagulant • other secretions; osteoarthritis

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