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Phylum Platyhelminythes

Phylum Platyhelminythes. Platyhelminthes. ~ 20,000 extant species Parasitic + free-living Unsegmented flatworms. Platyhelminthes. Triploblastic, acoelomate, bilaterally symmetrical Incomplete gut; absent in some parasitic forms Cephalization of nervous system

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Phylum Platyhelminythes

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  1. Phylum Platyhelminythes

  2. Platyhelminthes • ~ 20,000 extant species • Parasitic + free-living • Unsegmented flatworms

  3. Platyhelminthes • Triploblastic, acoelomate, bilaterally symmetrical • Incomplete gut; absent in some parasitic forms • Cephalization of nervous system • Protonephridia: excretion and osmoregulation • Hermaphroditic

  4. Support • Hydrostatic skeleton • Elastic body wall • Body musculature

  5. Taxonomy • Class Turbellaria • Class Monogenea • Class Trematoda • Class Cestoda

  6. Class Turbellaria • Free-living flatworms • Most are aquatic • Epidermis cellular and ciliated

  7. Feeding and digestion in Turbellaria • Consume invertebrates (few herbivores and omnivores) • Locate food via chemoreception • A few are symbiotic

  8. Turbellaria digestive system • Mouth, pharynx, intestine = incomplete gut • Pharyngeal glands produce mucus and proteolytic enzymes • Digestion extracellular, then phagocytization in intestine

  9. Turbellaria nervous system • Sense organs • Tactile receptors cover body - concentrated anteriorly • Chemoreception = location of food • Statocysts = gravity detection and orientation • Photoreceptors • Inverted pigment cup ocelli • Negative phototaxis

  10. Turbellaria nervous system • Variable: simple net-like to cephalized & bilateral • Ladder-like NS = more recently evolved

  11. Class Monogenea • Monogenetic flukes (life cycle = one host) • Body covered by tegument • Oral sucker reduced or absent • Ectoparasitic (usually fish)

  12. Class Monogenea • Monogenetic flukes (life cycle = one host) • Eggs hatch into ciliated larvae = oncomiracidia • Mature and find host

  13. Class Trematoda • Digenetic flukes (multiple hosts) • Body with tegument • One or more suckers present • Internal parasite

  14. Fluke Digestive System • Feed on host tissues and fluids (muscular pharynx) • Or, material in host gut • One-way digestive tract: mouth, muscular pharynx, short esophagus, intestinal cecae

  15. Fluke Nervous System • Ladder-like • Cerebral ganglion • Suckers with tactile receptors (bristles and spines)

  16. Sexual repro flukes • Hermaphroditic • Mutual cross fertilization • Male structures • Variable testes • Monogenetic = many • Digenetic = two • Sperm-to sperm duct, copulatory apparatus, eversible cirrus

  17. Sexual repro flukes • Female Structures • Ovary to oviduct to ootype • Oviduct joined by vitelline duct • Seminal receptacle = blind pouch off of oviduct • Single uterus sometimes modified as vagina near female gonopore

  18. Fluke reproduction • Mutual cross-fertilization • Sperm stored in seminal receptacle • Eggs - oviduct to ootype then fertilized • r-selected strategy (high fecundity)

  19. a – acetabulum • d - vitelline ducts • f - vitelline follicles • o - oral sucker • oe – oesophagus • oo – ootype • ov – ovary • ph – pharynx • sr - seminal receptable • t – testis • u - uterus

  20. Fluke life-cycles • Monogenetic • One host • Mostly external parasites of fish • Digenetic • Two or more hosts • Mostly internal parasites

  21. Fluke life-cycles: Chinese liver fluke

  22. Fluke life-cycles • Digenetic Fasciola = sheep liver fluke • Multiple hosts • Internal parasite of vertebrates • Intermediate host usually gastropod

  23. Fluke life-cycles Schistosoma mansoni Schistosomiasis = disease with problems from egg production, fevers, eggs lodged in various tissues

  24. Schistosomiasis

  25. Schistosoma spp. cause swimmer’s itch

  26. Class Cestoda • Tapeworms • Internal parasite • Body with tegument • Body with anterior scolex, short neck and proglottids • No digestive system

  27. Tapeworms = cestodes • Locomotion • Sedentary: adult on host intestinal wall • Capable of muscular undulations • Attachment • Scolex • Anterior with hooks or adhesive pad

  28. Tapeworm digestion • No mouth, no digestive tract • Nutrients absorbed across tegument

  29. Tapeworm Nervous System • Cerebral ganglion; nerve ring in scolex • Each proglottid has additional ganglia; connect to longitudinal nerve cords • Sensory organs reduced, tactile receptors in scolex

  30. Sexual Repro: tapeworms • Hermaphroditic • Mutual cross-fertilization • Self-fertilization in some

  31. Proglottids • Numerous testes along margins • Collecting tubules to coiled sperm duct • Vas deferens to genital pore

  32. Proglottids • Two ovaries • Uterus = blind sac

  33. Tapeworm sex and fertilization • Cirrus of each mate inserted into genital pores • Sperm stored, eggs fertilized in oviduct • Capsule material and yolk cells stored in uterus • When mature, proglottids break free

  34. Beef Tapeworm Life Cycle

  35. Pork Tapeworm Life Cycle

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