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Acoelomates

Acoelomates. Phylum Platyhelminthes Phylum Nemertea Phylum Gnathostomulida. Taxonomy. Acoelomate Phyla. Platyhelminthes Flat worms Nemertea Ribbon worms Gnathostomulida Jaw worms. Why bilateral symmetry?. Movement toward prey or host Cephalization Directional sense organs

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Acoelomates

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  1. Acoelomates Phylum Platyhelminthes Phylum Nemertea Phylum Gnathostomulida

  2. Taxonomy

  3. Acoelomate Phyla • Platyhelminthes • Flat worms • Nemertea • Ribbon worms • Gnathostomulida • Jaw worms

  4. Why bilateral symmetry? • Movement toward prey or host • Cephalization • Directional sense organs • Chemoreceptors • Ocelli (light sensing eyespots) • Rheoreceptors (sense water currents)

  5. Acoelomates Key Features • Three germ layers • Ectoderm, endoderm, mesoderm • Mesoderm forms muscle and mesenchyme • Organ-system level of organization • Cephalization • Excretory system • Some have circulatory and one-way alimentary canal

  6. Acoelomates Body Plan

  7. Phylum Platyhelminthes • Specialized Cells • Rhabdites - secrete mucous sheath • Tegument - outer covering of syncytial cells • Flame cells – Osmoregulation • Some have endolecithal egg cells – yolk contained within egg cell

  8. Platyhelminthes Cross Section

  9. Tegument • Syncytium • Apical cell membrane missing

  10. Flame Cell • Osmoregulation • Beating flagella creates negative pressure to draw fluid into chamber • Water is directed through channels then through an external pore

  11. Major Classes of Platyhelminthes • Class Turbellaria • Planaria – free living • Class Trematoda • Liver flukes – endoparasites • Class Monogenea • Fish ectoparasites • Class Cestoda • Tape worms – endoparasites

  12. Class Turbellaria • Key Features • Ladder like nervous system • Eye spots (Ocelli) • Auricles - chemoreceptors • Free living flatworms • Muscular and ciliary movement • Carnivorous

  13. Planarian Body Plan

  14. Class Trematoda • Similar in structure to Turbellaria • Special adaptation for endoparasitic life style • Cyst glands • Suckers and hooks for griping host • Digenetic – complex life cycle with multiple hosts

  15. Liver Fluke

  16. Liver Damage Caused By Flukes • Scar tissue • Blocked bile ducts

  17. Flukes in Liver Section

  18. Fasciolopsis - Anterior End

  19. Schistosoma mansoni • Blood fluke • Male and female are dioecious

  20. Schistosoma cercaria

  21. Class Cestoda • Tapeworms - endoparasites • Key Features • Lack a digestive system • Composed of reproductive units called proglottids • Adult tegument covered in microvilli-like projections – increases surface area, non-ciliated

  22. Tapeworm • New proglottids are added just behind the scolex

  23. Tapeworm Tegument • Microvilli help with food adsorption • Sensory cells – no other sense organs

  24. Mature Proglottid • Reproductive unit • Mature proglottids are either shed or produce shelled embryos • Each proglottid has both male and female organs

  25. Tape WormLife Cycle

  26. Taenia soliumPork tapeworm

  27. Taenia Cyst in Muscle

  28. Phylum Nemertea • Ribbon worms • Ciliated epidermis • Locomotion – gliding over slime track and muscular contraction • Complete digestive tract – mouth and anus • Extracellular digestion • Proboscis to capture prey

  29. Amphiporus

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