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Worms

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Worms

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  1. Worms Chapter 27

  2. Flatworm characteristics • Soft, flattened bodies • Simplest animals with three embryonic germ layers • Bilateral symmetry • Cephalization: head formation • Acoelomate: fluid filled body cavity made of mesoderm tissue

  3. Flatworm feeding styles • Carnivorous: feed on tiny aquatic animals • Scavengers: feed on recently dead animals • Parasites: blood, tissue fluids, cells within host’s body • Lack complex digestive system because host partially digests food • Ex: tapeworm (no digestive system at all)

  4. Feeding • Mouth only • Pharynx: muscular tube, extended from mouth • Digested food and nutrients absorbed in the digestive cavity

  5. Branched digestive system translucent species Aquaplana/Paraplanocera sp. extends throughout the entire body Photo by Robert F. Bolland). 

  6. Respiration, Circulation, & Excretion • Flat and thin body shape requires little circulation. • Diffusion transports oxygen and nutrients to internal tissues • Diffusion removes CO2 and waste • Flame cells: specialized cells that remove excess water from body • helps to remove metabolic waste (ammonia and urea)

  7. Flame-bulb excretory system

  8. Response • Ganglia: group of nerve cells with two long nerve cords • Eyespots: group of cells that can detect changes in light intensity

  9. The Anatomy of a Flatworm Section 27-1 Eyespot Freshwater flatworms have simple ganglia and nerve cords that run the length of the body. The excretory system consists of a network of tubules connected to flame cells that remove excess water and cell wastes. Ganglia Head Nervecords Gastrovascularcavity Flatworms use a pharynx to suck food into the gastrovascular cavity. Digested food diffuses from the cavity into other cells of the body. Eyespots in somespecies detect light. Excretorysystem Ovary Testes Mouth Pharynx Most flatworms are hermaphrodites, having male reproductive organs (testes) and female reproductive organs (ovaries) in the same organism. Flame cell Excretorytubule Figure 27–3 

  10. Planarian with noticeable eyespots

  11. Eyespots of a planarian

  12. Movement • Cilia on epidermal cells • Nerve controlled muscle cells Muscle filament staining of a turbellarian flatworm reveals a meshwork of longitudinal, circular and diagonal muscles. The large, bright ring with muscle fibers radiating outward is the muscular pharynx plicatus Image by M. D. Hooge and S. Tyler, Department of Biological Sciences, University of Maine).

  13. Groups of flatworms • Turbellarians: free living, marine & freshwater • Flukes: parasitic, infects internal organs of host • Tapeworms: parasitic, adapted to life inside host’s intestines

  14. Turbellarian

  15. Brightly colored turbellarian

  16. Turbellarian reproduction Asexual - fission

  17. Primary host (human) Intermediate host(snail) Life cycle of fluke Section 27-1 Flukes mature and reproduce sexually in the blood vessels of human intestines. Embryos are released and passed out with feces. Adult fluke Human intestine Embryo Ciliated larva Tailed larva After asexualreproduction, newlarvae are releasedfrom the snail into the water. They then infect humans, the primary host, by burrowing through the skin. If they get into the water, embryos develop into swimming larvae that infect an intermediate host (snail). Species: Schistosoma Mansoni

  18. Brachylaimacribbi fluke • (A) adult worm • (B) two suckers and spiny coat • (C) sperm deposited from pore

  19. Tapeworm

  20. Proglottid: tapeworm segment • Proglottid with fertilized eggs bursts open to release zygotes

  21. Scolex: head with suckers or hooks Human tapeworm Parasitic tapeworm from fish

  22. Intermediate hosts • Tapeworm larvae burrow into cow or fish muscle tissue, which infects the animal that eats this tissue. Rat tapeworm

  23. Roundworms C. elegans

  24. Roundworm characteristics • Unsegmented • Tapering ends • Variety of environments and climates

  25. Roundworm characteristics • Pseudocoelomate: body cavity lined partially with mesoderm tissue • Two digestive tract openings, mouth and anus

  26. Length of roundworm • Microscopic to 1 m in length

  27. Feeding • Predators with grasping mouthparts • Spines to catch and eat small animals • Detritovores parasitic hookworm

  28. Respiration, Circulation, & Excretion • Gas exchange through body walls • Metabolic waste excretion through body walls • No internal transport system

  29. Response and movement • Simple nervous system of ganglia • Hydrostatic pressure to move around • Muscular contractions to move through water

  30. Reproduction • Sexually • Male or female reproductive system • Internal fertilization: male deposits sperm into female • Complex life cycles in parasitic roundworms

  31. Guinea worm disease

  32. Pinworm infection in child’s intestine

  33. Trichinella life cycle

  34. Filarial worms • Primary cause of elephantiasis condition where parts of the body are swollen • Requires arthropod intermediate host to complete life cycle

  35. Ascarid worms

  36. Hookworm life cycle

  37. C. elegans and research • First multicellular animal to have entire genome sequenced • Every body cell’s developmental pathway is also recorded.

  38. Segmentedworms

  39. Annelid characteristics • Segmented bodies • True coelom: body cavity lined with mesoderm tissue • Mouth and anus

  40. Anus Setae Body segments Dorsalblood vessel Gizzard Crop Clitellum Mouth Brain Ganglion Circular muscle Ventralblood vessel Ringvessels Reproductiveorgans Ganglia Nephridia Longitudinalmuscle The Anatomy of an Earthworm Section 27-3 Figure 27–16 

  41. Feeding and Digestion • Filter feeders • Predators • Pharynx that may be collect or capture (if jawed) food • Food moved into esophagus, crop for storage, gizzard for grinding, digestive tract for absorption

  42. Circulation • Closed circulatory system: blood contained within network of blood vessels • Two major blood vessels running from head to tail • Dorsal vessel: blood towards head, functions like heart • Ventral vessel: blood towards tail

  43. Respiration • Gills: specialized for underwater gas exchange in aquatic worms (ex: tube worms) • Terrestrial annelids perform gas exchange through their moist skin.

  44. Tubeworms

  45. Excretion • Nephridia: organs that filter fluid in the coelom

  46. Response • Most have well-developed nervous systems with brain and nerve cords • Marine annelids have the best adapted nervous system.

  47. Movement • Marine annelids may have parapodia, paddlelike appendages. • Hydrostatic skeleton: longitudinal and circular muscles • Longitudinal: contract to make worm shorter and fatter • Circular: contract to make worm longer and thinner

  48. Reproduction • Sexual reproduction • External fertilization • May be single sex or hermaphrodite • Clitellum band thickens, secreting mucus ring with eggs where sperm are deposited • Fertilized eggs slips off with the mucus ring, which forms a cocoon where the young worms hatch later.

  49. Clitellum