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Platyhelminthes

Platyhelminthes. Acoelomate Flatworms. Today’s Objective. TSW take notes on the phylum Platyhelminthes including economic importance, an overview of class characteristics, and ecological niches. General Flatworm Characteristics. Acoelomate – no body cavity coelom- solid mesenchyme (mesoderm)

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Platyhelminthes

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  1. Platyhelminthes Acoelomate Flatworms

  2. Today’s Objective • TSW take notes on the phylum Platyhelminthes including economic importance, an overview of class characteristics, and ecological niches.

  3. General Flatworm Characteristics • Acoelomate – no body cavity coelom- solid mesenchyme (mesoderm) • First phylum to show a definite cellular mesoderm • Bilaterally symmetrical • Triploblastic; 3 distinct tissue or germ layers • Dorsoventrally flattened

  4. General Characteristics (cont.) • Respiration by diffusion • Digestive system extensively branched • One opening for feeding and waste removal • Lack an anus • Primitive kidneys – protonephridia with “FLAME CELLS”

  5. General Charcterisitcs (cont.) • First evidence of cephalization primitive brain • Some have eyespots • Directional movement • No true respiratory system or circulatory system • Usually hermaphroditic

  6. Class Turbellaria • Free-living flatworms • Some freshwater (Planaria), marine, or terrestrial • Most move by circular and longitudinal muscles • Some move by using cilia (or cilia + mucus)

  7. Turbellarian Feeding - Carnivorous • Wrap body around prey • Entangling with mucous • Ingest the whole prey or suck its juices through a hardened stylet (modified pharynx) • in many species the pharynx is completely eversible and can envelope the entire prey • there is no anus so ingestion and egestion are through the mouth

  8. Turbellarian Reproduction • Sexual Reproduction • Most hermaphroditic • Both sex organs discharge gametes into a common chamber even though this is true- cross fertilization is the most common mode of reproduction • Some self fertilization can and does occur • Asexual Reproduction • Fragmentation and Regeneration

  9. Dugesia

  10. Class Monogenea • Parasitic • Flukes • Only one host • Most external parasites • Gyrodactylus • Polystoma • Can cause major economic losses to fisheries

  11. Class Trematoda • Digenetic Flukes • Complex life history, involves 2 or more hosts • Live in every type of environment • 5,000+ known species • Live mostly in digestive system or associated organs (all parasitic)

  12. Some Trematodes of Importance • Clonorchis – Chinese human liver fluke • Fasciola hepatica – Liver fluke • Schistosoma – Blood fluke • Know this life cycle! • Where they are present it is hazardous to bathe, drink, wade in or dip your arms in infested waters!

  13. Class Cestoda - Tapeworms • Long, Flattened • White or Yellow in color • All parasitic! • Adults almost always live in the intestines of their hosts • Body has protective cuticle • Head (scolex) has multiple disks of hooks for attachment

  14. Cestodes (cont.) • Can reach up to 50 ft. in length! • No specialized sense organs • Reproduce using proglottids (segments) • Contain flame cells, nerves, muscles, male and female reproductive organs • Shed in feces of host • Taenia saginata – beef tapeworm • Taenia solium – pork tapeworm

  15. Tapeworm Structure

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