Flatworms, Roundworms, & Rotifers

1. Flatworms, Roundworms, & Rotifers Chapter 34

2. Phylum Platyhelminthes Section 34.1

3. General Structure: • 3 germ layers– ectoderm, mesoderm, and endoderm • acoelomates • Bilateral symmetry • Anterior and posterior ends • Dorsal and ventral surfaces only • Flat body plan • Flatworms!

4. General Functions: • Exchange oxygen and carbon dioxide directly with the environment to cells by diffusion • No circulatory system or respiratory system needed • Only one opening where food and wastes pass through! • Cephalization

5. Classification: • Four Classes: • Turbellaria - non-parasitic • Trematoda- parasitic • Monogenea - parasitic • Cestoda–parasitic

6. 1. Class Turbellaria: • 4,500 species • Mostly marine • Swim in wavelike motion • Glide over solid surfaces on layer of mucus • Example: Planarian Dugesia • freshwater Video

7. Planarian Body Plan:

8. Planarian Organ Systems: Digestive System: • Scavengers & predators • Decaying plants & animal matter • Prey on smaller organism • Pharynx – throat that extends to the middle of body • video Pharynx

9. Planarian Organ Systems: Excretory System: • Flame Cells – enclosed tufts of cilia that draw excess water together and excretes it through pores • video Flame Cells

10. Planarian Organ Systems: Nervous System: • Cerebral ganglia: two clusters of nerve cells at anterior • “Brain” • Can learn • Eyespots: sense direction and intensity of light • Other senses: touch, water currents, chemicals

11. Planarian Organ Systems: Reproductive System: • Sexual: • Hermaphrodites • Eggs laid in protective capsule • Hatch in 2-3 weeks • Asexual: • Regeneration

12. 2. Class Trematoda & 3. Class Monogenea: • Both are parasitic flukes • Leaf-shaped flatworms • Endoparasites: • Live in blood, intestines, lungs, liver, etc. • Ectoparasites: • Live on external surfaces of aquatic hosts

13. Structure of Flukes • Anterior & ventral suckers for attachment to host • Nervous system like planarian • Except NO eyespots • Tegument – outer layer that protects from host’s immune and digestive system

14. Liver fluke

15. Reproduction of flukes: • Most are hermaphroditic • May release 10,000+ eggs at a time! • Complicated life cycle (p. 692)

16. Life Cycle: • Primary host:adult parasite gets nourishment from this host • Sexual reproduction • Intermediate host: larvae derive nourishment here • Asexual reproduction

17. Fluke Diseases in Humans • Swimmer’s itch: minor skin irritation and swelling • Small brown fluke in lakes (in Ohio) • Dies within skin because humans are not ideal hosts

18. Swimmer’s itch

19. Schistomiasis (blood fluke): • disease that causes tissue damage, bleeding, tissue decay and possible death • Lungs, intestine, bladder, & liver • 200 million people affected worldwide Human- Primary host Snail- Secondary or Intermediate host Animation!

20. WHO Info.

21. 4. Class Cestoda • 5,000 species of tapeworms • Can live in intestines of most vertebrates • Enter through undercooked food with eggs or larvae • Symptoms of infection: • Digestive problems • Weight loss • Lack of energy • anemia

22. Structure: • Tegument to protect from host • Also absorbs nutrients from host • Scolex: knob-shaped organ with hooks and suckers to attach to host • Proglottids: body sections after a short neck • Up to 2,000 per tapeworm!

23. Reproduction: • Hermaphrodites • Each proglottid has ovaries and testes • Filled with 100,000+ eggs each! • Eggs fertilized by sperm of different proglottid

24. Life Cycle: • Cysts: dormant larvae surrounded by protective covering in animal muscle

25. Phylum Nematoda & Rotifera Section 34.2

26. General Characteristics: • Bilateral symmetry • Fluid filled body cavity • pseudocoelomate • Holds internal organs • Stores sperm & eggs • Supports body • Structure that muscles can contract against

27. Phylum Nematoda • Roundworms • Long, slender bodies that taper at both ends • 1mm to 4ft • Digestive tract with 2 openings • Anterior – mouth • Posterior – anus • One directional movement

28. Continued… • Most have separate sexes • Cuticle – protective covering • Free-living on land, salt and freshwater • 15,000 species known • 150 species parasitic to plants and animals • Humans are host to 50 species!

29. Ascaris: • Roundworm parasite that lives in intestine • Pigs, horses, & humans • Can totally block host’s intestine • Up to a foot in length • Female produces 200,000 eggs/day

30. Video

31. Life Cycle: • Eggs leave with feces and enter soil • Enter humans with contaminated food and water • Larvae enter intestines and move to blood stream, then lungs, coughed up and swallowed back to intestines where they mate and reproduce

32. Hookworms: • Another intestinal parasite • Mouth has cutting plates that clamp onto intestine wall • Feed on host’s blood which may lead to anemia • May cause slow mental and physical development in children • Affects 1 billion people in tropical and subtropical regions

33. Hookworm • Enter host by boring through the feet Video

34. Life Cycle: • Eggs leave with feces • Larvae develop in soil • Enter host’s feet • Hitch a ride with blood to the lungs • Coughed up and swallowed to intestines where adult develop

35. Trichinella: • Infect humans and pigs • Adults embed in walls of intestine • Larvae travel via blood to muscles • Form cysts • Humans get it from eating undercooked pork • Causes disease trichinosis • Muscle pain & stiffness • Can cause death Video

36. Pinworm – most common in U.S. • Live and mate in lower intestine • Female crawls out at night and lays eggs around anus • Person scratches during sleep and spreads eggs to everything touched • Eggs ingested and hatch

37. Pinworm

38. Filarial worms – 250 million people infected in tropics • Found in lymphatic system (collects excess fluid from blood vessels) • Can cause elephantiasis • Swollen limbs, skin hardens & thickens • Can cause heartwormin dogs and cats • Spread by mosquitoes

39. Phylum Rotifera • Most are transparent (see-through) • Free-living in freshwater • 100 to 50 micrometers • No water = dry up and look like grains of sand; when water is present again they go back to normal • Cool adaptation!

40. Rotifer Structures: • Cilia –sweep food into mouth • Mastax – breaks down food • Stomach • Intestine – absorbs nutrients • Cloaca – digestive, reproductive, and excretory systems empty here • Universal hole • Flame cells – pull excess water together • Anus – hole to the outside

41. Body Parts: video

42. Have cerebral ganglia and eyespots • Reproduction by: • Parthenogenesis – unfertilized eggs become adult females