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Platyhelminthes The Flatworms

Platyhelminthes The Flatworms. Pechenik: 34,000 spp (Brusca & Brusca: 20,000 spp) Characteristics: Triploblastic Ectoderm, mesoderm, endoderm Acoelomate Bilateral symmetry (w some cephalization) Protonephridia = Organs for excretion/osmoregulation Flatness allows diffusion for gas exchange

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Platyhelminthes The Flatworms

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  1. PlatyhelminthesThe Flatworms • Pechenik: 34,000 spp (Brusca & Brusca: 20,000 spp) Characteristics: • Triploblastic • Ectoderm, mesoderm, endoderm • Acoelomate • Bilateral symmetry (w some cephalization) • Protonephridia = Organs for excretion/osmoregulation • Flatness allows diffusion for gas exchange • 80% are parasitic • Simultaneous hermaphrodites (monoecious)

  2. Opisthaptor Ectoparasite One host Trematoda Acetabulum endoparasite Mollusc/vertebrate life cycle Cestoda Monogenea Turbellaria Free living Microtriches Scolex Proglottids Cilia lost from ectoderm (parasitic lifestyle) Phylum Platyhelminthes

  3. Class Turbellaria

  4. Class Turbellaria

  5. Class Turbellaria

  6. Class Turbellaria

  7. Class Turbellaria

  8. Class Turbellaria • Most are free living • Marine & FW • Sensory receptors • Chemical (auricles) • Tactile • Light Dugesia sp.

  9. Class Turbellaria • Most are free living • Marine & FW • Sensory receptors • Chemical • Tactile • Light • Cephalized • Crawl on substrate using cilia Dugesia sp.

  10. Class Turbellaria • Incomplete digestive tract Pharynx

  11. Class Monogenea haptor opisthaptor

  12. Class Monogenea Ectoparasites of fish skin and gills Only 1 host

  13. Monogenea Reproduction: Eggs → oncomiracidium larva → attach to fish Larva similar to cestode oncosphere Adults resemble digene trematoda (convergent evolution – life cycles very different)

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