Phylum: Platyhelminthes

1. Phylum: Platyhelminthes • “flatworms” • Examples: tapeworms, flukes, planarians

2. Traits • Flattened, worm-like body

3. Traits • Bilateral symmetry

4. Traits • Cephalized – have a distinct head end with a concentration of sensory nerves and brain

5. Traits • Ladder-like nervous system

6. Traits • 3 cell layers

7. Traits • Blind sac digestive system

8. Types • Planarians – free living flatworms • Tapeworms – segmented parasitic flatworms • Flukes – non segmented parasitic flatworms

9. Planarian structure • Ectoderm (epidermis) – outside layer of cells • Endoderm – inside layer of cells • Mesoderm – the middle layer of cells

10. Mesoderm • Advantage – allows for the development of complex internal organs • Disadvantage – since not every cell is in contact with the water, getting oxygen and getting rid of wastes is a problem

11. Planarian structure • Eyespot – detects light but can’t see shapes and images

12. Planarian structure • Flame cells – excretory structures, collect nitrogenous wastes and force them out of the body through a series of tubes

13. Planarian structure • Digestive system – blind sac, branches a lot so no cell is very far from food

14. Movement • Can glide on ventral cilia or use muscles to swim

15. Reproduction • Asexual – by regeneration or binary fission

16. Binary Fission

17. Reproduction • Sexual – hermaphrodites, must exchange sperm (mate) with another worm

18. Tapeworms • Segmented parasitic flatworms

19. Advantages of parasitism • Food is readily available • don’t waste energy through movement • protected from the environment

20. Disadvantages of parasitism • If the host dies, they die • Must get offspring to another host • Must produce a lot of offspring

21. Tapeworm Structure • Scolex – head of a tapeworm

22. Tapeworm Structure • Hooks and suckers – attach the tapeworm to the host’s intestinal wall

23. Tapeworm Structure • Neck – pinches off proglottids

24. Tapeworm Structure • Proglottids – reproductive segments of a tapeworm

25. Tapeworm Structure • Cuticle – non cellular outside layer that keeps them from being digested from the host’s enzymes

26. Tapeworm Infestations

27. Symptoms • Weight loss and fatigue • Final diagnosis is from a stool sample

29. Cure • Easy • Since they live in the intestines, the medicine goes directly to them, then they are eliminated with the feces

30. Life Cycle • Adults live in the human intestines, mate, eggs leave with the feces • A pig ingests food or water contaminated with the eggs • Eventually lodge and form cysts in pig’s muscle • A human eats poorly cooked pork and it starts all over again

31. BEEF TAPEWORM LIFE CYCLE 5. Uncooked meat in consumed 1. eggs released 3. eggs eaten 4. larvae migrate to muscle & form cysts 2. eggs on grass

32. Cysts in contaminated pork

33. Prevention • Cook meat well • Good sewage systems

34. Flukes • Non segmented parasitic flatworms

35. Flukes • Endoparasites – live inside the body

36. Cure? • Very difficult • Since they live in liver, medicine doesn’t go directly to them • If you do kill them, the body can’t eliminate them easily

37. Sheep liver fluke • Live in a sheep’s liver • Can clog the bile duct and possibly kill the sheep

38. Alternation of hosts • Need at least 2 separate hosts to complete its life cycle

39. Life cycle • Adults live inside the sheep’s liver, mate, eggs leave with feces • Hatch into larvae which enter snails, reproduce asexually • Leave snails and form cysts on grass which is eaten by the sheep and start over

41. Prevention • Spray and kill the snails

42. Chinese liver fluke • Infest the liver of humans

43. Life cycle • Adults live in the human liver, mate, eggs leave with feces which is used to fertilize fields • Flood irrigation washes them into rivers, hatch into larvae which enter snails, reproduce asexually • Leave snails and enter fish which are eaten raw by humans and start over

45. Prevention • Cook the fish • Use other fertilizers • Other irrigation methods