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Diversity and Adaptations of Platyhelminthes, Malformed Frogs, Nematoda, and Annelida

Explore the characteristics, ecological roles, and impacts of Platyhelminthes, Malformed Frogs, Nematoda, and Annelida in various environments, including marine, freshwater, terrestrial, and parasitic habitats. Learn about hermaphroditic reproduction, malformations in frogs, and the success of soil nematodes. Delve into the unique features of segmented worms and their role in ecosystems.

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Diversity and Adaptations of Platyhelminthes, Malformed Frogs, Nematoda, and Annelida

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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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