Flatworms, Roundworms, and Rotifers

1. Flatworms, Roundworms, and Rotifers

2. Germ Layers • Layers of cells that originate in the developing embryo and become specific structures • Ectoderm - outer • Mesoderm - middle • Endoderm - inner

3. Body Plans Acoelomate • Without a coelom • 2 germ layers • Ectoderm and endoderm • Not separated by a cavity • Least complex body plan • Sponges and cnidarians

4. 3 Layer Acoelomate • 3 germ layers • Endoderm, mesoderm and ectoderm • Not separated by a cavity • Flatworms

5. Pseudocoelomate • Pseudocoelom • Cavity formed between mesoderm and endoderm • Roundworms and rotifers

6. Coelomate • Cavity developed within the mesoderm • Most complex body plan • Mollusks, annelids, arthropods, echinoderms, and chordates

7. Phylum Platyhelminthes - Flatworms • 13,000 species • Bilaterally symmetrical • Cephalization • 3 classes (Turbellaria, Trematoda, and Cestoda) • Trematodes and cestodes parasitic • Parasites live in or on other organisms (host)

8. Parasitic Flatworms • Originated from free living • Some organs modified for parasitism • Lack mouths • Well developed digestive system

9. Hooks or suckers • Tegument- thick covering of cells • Cuticle- nonliving layer secreted by epidermis

10. Class Turbellaria • 3000 species • Most marine • Ex. Planaria (fresh water)

11. Planaria External anatomy • Anterior end spade shaped • Posterior end tapered • Body covered with cilia

12. Movement • Move by undulative motion or • Laying down mucus layer and beating cilia

13. Digestion and Excretion • Scavenger (carrion) • Predator (small prey)

14. Digestion • Muscular pharynx extended out of mouth • Food sucked in • Passed into intestines (branched) • Nutrients absorbed through intestinal wall or phagocytosis • Undigested food excreted through pharynx and mouth

15. Excretion • Chemical wastes and excess water eliminated by network of ducts (pores and canals) • Contains flame cells • Flame cells enclose a tuft of beating cilia • Cilia moves wastes into the ducts -> • Excretory pores -> out

16. Nervous Control • Organized and cephalized • Sense light intensity and direction • Two anterior eyespots (photosensitive cells) • Touch, taste, and smell receptors

17. Two anterior ganglia (clusters of nerves) -> simple brain • Two longitudinal nerves connected by transverse nerves • Capable of simple "learning" • Memory stored chemically

18. Reproduction • Hermaphrodites • Sexual reproduction • Simultaneous fertilization • Protective encapsulated eggs stick to rock • Hatch 2-3 weeks

19. Asexual (summer) • Attach to rock surface with posterior end • Stretch until they tear into two • Each half regenerates lost parts

20. Class Trematoda • 6,000 species • Parasitic - both endoparasites and ectoparasites • Leaf shaped

21. Structure and Reproduction of Flukes • Parasites • 1 cm long (oval shaped) • Unciliated tegument

22. 2 sucker mouths (anterior and ventral) • Cling to host • Anterior sucker sucks in blood, cells and fluids of host

23. Nervous and Excretory System • Turbellarian like • Reproduction • Complex reproductive life cycle • Hermaphroditic • Long coiled uterus (stores eggs (10,000+) • Eggs released through genital pore -> larvae

24. Life Cycle • Adults live in sheep liver and gall bladder where they mate and produce eggs • Eggs enter intestines -> • Eliminated with feces -> • Eggs hatch in water ->

25. Larvae invade snail -> • Multiply asexually -> • Leave snail and form cysts -> • Cysts dormant larvae with hard protective covering

26. Ingested by sheep -> • Hatch in digestive tract -> • Bore through intestines into blood -> • Mature and reproduce in liver

27. Schistosomiasis • Blood fluke - schistosoma • Infects 200-300 million people (asia, africa, and so. America) • Around lakes and rivers • Spread via irrigation ditches and reservoirs

28. Adults live in human bloodstream • Eggs lodge in veins, lungs, intestines, bladder, and liver • Block blood vessels • Cause internal bleeding and tissue decay

29. Class Cestoda - Tapeworms • 1,500 species • Most parasitic (7 in humans) • Adapted for parasitic life • Tough outer tegument

30. Hooks and suckers • Nervous system extends length of body • Lack sense organs, mouth, and digestive tract

31. Absorb nutrients directly through heavily folded tegument • Knoblike head with hooks and suckers (scolex) • Grows by producing body segments (proglottids) • Oldest proglottids at posterior • Excretory system drains proglottids of waste • Life cycle and reproduction

32. Proglottids contain both male and female reproductive organs • Cross fertilization is typical between individuals or proglottids • After fertilization - proglottids break off and are eliminated with feces

33. Beef tapeworm • Cattle eat grass with proglottids and eggs • Larvae hatch • Bore through cow's intestine -> blood stream

34. Burrow into muscle tissue and form cysts • Human eats beef (muscle) -> intestine • Cysts wall dissolves and bladder worm released • Develops into an adult beef tapeworm

35. Nematoda and Rotifera • Pseudocoelom • Lined on the inside by endoderm and outside by mesoderm • Fluid filled • Contains organs

36. Supports the body • Provides hydrostatic pressure against which muscles can contract • Serves as a storage area for wastes or eggs and sperm

37. Phylum Nematoda - Roundworms • 10,000 - 80,000 (million) species • Long slender bodies that taper at both ends • Flexible protective cuticle

38. Digestive tract with two opening (1 way) • Anterior mouth • Posterior anus • Sexes distinct in most species • Guinea worm female = 120 cm • Male = 2.5 cm)

39. Excretory wastes collected by system of tubes • Expelled through excretory pore in posterior end • Longitudinal muscles, lack circular muscle -> thrashing motion • Most free living

40. Many plant and animal parasites (enormous economic damage) • Humans host 50 species • More than 1/3 of humans infected

41. Ascaris • Found in the intestines of pigs, horses, and humans • Enter body in contaminated food or water • Hatch in intestines • Larvae bore into the blood stream

42. Carried to the lungs and throat • Coughed up, swallowed, returned to intestines • Mature and mate • Block intestines -> death

43. Larvae in lungs cause respiratory illness • Females produce 200,000 eggs/day (contain 27 million eggs) • Shed through genital pore • Exit in hosts feces

44. Ancylostoma and Necator - Hookworms • Ancylostoma - effects 40 million people • Necator - effects 360 million people • Both tropical and semi-tropical • Cutting plates hook into intestinal wall • Feed on hosts blood -> anemia Attached to intestinal wall Migrating larvae

45. Travels via blood to lungs and throat where swallowed -> • Mate in intestines -> • Eggs shed in feces -> • Hatch on moist soil -> • Larvae bore through feet or new host

46. Trichinella • Causes trichinosis • Undercooked pork contaminated with cysts • Cysts released larvae • Larvae burrow into wall of small intestines

47. Mature into adults -> • Adults produce larvae -> • Pass into blood and form cysts in muscles -> • Causing pain and suffering ->

48. Rotifera • 1,750 species • Transparent, free swimming and microscopic • Freshwater and marine • Crown of cilia surrounding mouth

49. Cilia sweep food into mouth • Look like rotating wheel • Feed on unicellular algae, bacteria, and protozoa • Moves through pharynx -> mastax • Mastax (muscular organ) chops up food

50. Hydrostatic pressure inside pseudocoelom • Nervous system composed of anterior ganglia and two long longitudinal nerves • Two anterior eye spots