Chapter 36: Flatworms, Roundworms, and Rotifers

1. Chapter 36: Flatworms, Roundworms, and Rotifers Objectives: State the distinguishing characteristics of flatworms Describe the anatomy of a planarian Compare and contrast free-living and parasitic flatworms Diagram the life cycle of a fluke Describe the life cycle of a tapeworm Describe the body plan of a pseudocoelomate Explain the relationship between humans and three types of parasitic roundworms Describe the anatomy of a rotifer

2. 36-1: Platyhelminthes • Members of the phylum Platyhelminthes are called flatworms. • Their bodies develop from three germ layers and are more complex than those of sponges, cnidarians, and ctenophores. • Flatworms have Bilateral symmetry, with dorsal and ventral surfaces, right and left sides, and anterior and posterior ends.

3. What Is a Flatworm? • Flatworms are soft, flattened worms that have tissues and internal organ systems. • They are the simplest animals to have three embryonic germ layers, bilateral symmetry, and cephalization.

4. What Is a Flatworm? • Flatworms are acoelomates, which means they have no coelom. • A coelom is a fluid-filled body cavity that is lined with tissue derived from mesoderm. • The digestive cavity is the only body cavity in a flatworm. • Flatworms have bilateral symmetry.

5. What Is a Flatworm? • Three germ layers of a flatworm

6. Form and Function in Flatworms • Flatworms are thin and most of their cells are close to the external environment. • All flatworms rely on diffusion for respiration, excretion, and circulation.

7. Form and Function in Flatworms • Free-living flatworms have organ systems for digestion, excretion, response, and reproduction. • Parasitic species are typically simpler in structure than free-living flatworms.

8. Form and Function in Flatworms • Feeding  • Flatworms have a digestive cavity with a single opening through which both food and wastes pass. • Near the mouth is a muscular tube called a pharynx. • Flatworms extend the pharynx out of the mouth. The pharynx then pumps food into the digestive cavity.

9. Form and Function in Flatworms • Most parasitic worms do not need a complex digestive system. • They obtain nutrients from foods that have already been digested by their host.

10. Form and Function in Flatworms • Respiration, Circulation, and Excretion  • Flatworms do not need a circulatory system to transport materials. •  Flatworms rely on diffusion to • transport oxygen and nutrients to their internal tissues, and • to remove carbon dioxide and other wastes from their bodies.

11. Form and Function in Flatworms • Flatworms have no gills or respiratory organs, heart, blood vessels, or blood. • Some flatworms have flame cells which are specialized cells that remove excess water from the body. • Flame cells may filter and remove metabolic wastes.

12. Form and Function in Flatworms • Response   • In free-living flatworms, a head encloses ganglia, or groups of nerve cells, that control the nervous system. • Two long nerve cords run from the ganglia along both sides of the body.

13. Form and Function in Flatworms • Many free-living flatworms have eyespots. • Eyespots are groups of cells that can detect changes in light. • Most flatworms have specialized cells that detect external stimuli. • The nervous systems of free-living flatworms allow them to gather information from their environment.

14. Form and Function in Flatworms • Digestive Structures of a Planarian

15. Ganglia Nerve cords • Excretory, Nervous, and Reproductive Structures of a Planarian Excretory system Ovary Testes Flame cell Excretory tubule

16. Form and Function in Flatworms • Movement   • Free-living flatworms move in two ways. • Cilia on their epidermal cells help them glide through the water and over the bottom of a stream or pond. • Muscle cells controlled by the nervous system allow them to twist and turn.

17. Form and Function in Flatworms • Reproduction  • Most free-living flatworms are hermaphrodites that reproduce sexually. • A hermaphrodite is an individual that has both male and female reproductive organs. • Two worms join in a pair and deliver sperm to each other. • The eggs are laid in clusters and hatch within a few weeks.

18. Form and Function in Flatworms • Asexual reproduction takes place by fission, in which an organism splits in two. • Each half grows new parts to become a complete organism. • Parasitic flatworms often have complex life cycles that involve both sexual and asexual reproduction.

19. Classesof Flatworms • What are the characteristics of the three Classes of flatworms?

20. Classesof Flatworms • The three main groups of flatworms are • turbellarians • Trematoda- flukes • Cestoda- tapeworms • Most turbellarians are free-living. • Most other flatworm species are parasites.

21. Classes of Flatworms • Class Turbellarians • Turbellarians are free-living flatworms. Most live in marine or fresh water. • Most species live in the sand or mud under stones and shells.

22. Classesof Flatworms • Class Trematoda- Flukes • Flukes are parasitic flatworms. Most flukes infect the internal organs of their host. Usually don’t kill the host. • Host are typically Animals and humans • No special sense organs • Mostly aquatic • Most less than 1cm long • Schistosoma- Genus of flukes that cause Schistosomiasis.

23. Form and Function in Flatworms • Flukes can infect the blood or organs of the host. • Some flukes are external parasites. • In the typical life cycle of parasitic flukes, the fluke lives in multiple hosts.

24. Form and Function in Flatworms • Life Cycle of a Blood Fluke

25. Form and Function in Flatworms • A blood fluke’s primary host is a human. • Blood flukes infect humans by burrowing through the skin. Human intestine Tailed larva

26. Form and Function in Flatworms • Once inside the human, they are carried to the blood vessels of the intestines. • In the intestines the flukes mature and reproduce. • Embryos are released and are passed out of the body with feces. Adult fluke Embryo

27. Form and Function in Flatworms Embryo • If the embryos reach water, they develop into swimming larvae that infect a snail (the intermediate host). • An intermediate host is an organism in which a parasite reproduces asexually. Ciliated larva Life Cycle of a Blood Fluke

28. Form and Function in Flatworms • Larvae that result from asexual reproduction are released from the snail into the water to begin the cycle again. Life Cycle of a Blood Fluke

29. Form and Function in Flatworms • Class Cestoda- Tapeworms • Tapeworms are long, flat, parasitic worms that are adapted to life inside the intestines of their hosts. • No organs for locomotion, senses, or digestion. They absorb from the hosts digestive system. • Can be up to 40 feet long.

30. Form and Function in Flatworms • Tapeworms have no digestive tract and absorb digested food directly through their body walls. • The head of an adult tapeworm, called a scolex, is a structure that can contain suckers or hooks. • The tapeworm uses its scolex to attach to the intestinal wall of its host.

31. Form and Function in Flatworms • Structures of a Tapeworm

32. Form and Function in Flatworms • Proglottidsare the segments that make up most of the worm's body. • Mature proglottids contain both male and female reproductive organs. • Sperm produced by the testes (male reproductive organs), can fertilize eggs of other tapeworms or of the same individual.

33. Form and Function in Flatworms • After the eggs are fertilized, the proglottids break off and burst to release the zygotes. • The zygotes are passed out of the host in feces. • The eggs ingested by an intermediate host hatch and grow into larvae. • Larvae burrow into the intermediate host’s muscle tissue.

34. Form and Function in Flatworms • Larvae form a dormant protective stage called a cyst. • If a human eats incompletely cooked meat containing these cysts, the larvae become active and grow into adult worms within the human’s intestines, beginning the cycle again.

35. 36-2: Nematoda and Rotifera • Members of the Phyla Nematoda and Rotifera have bilateral symmetry and contain a fluid-filled space. • This space holds the internal organs and serves as a storage area for eggs and sperm. • It also supports the body and provides a structure against which the muscles can contract.

36. Phylum Nematoda • Nematoda is made up of roundworms, worms with long slender bodies that taper at both ends. • Roundworms are Pseudocoelomates • Pseudocoelomates is a hollow fluid filled cavity that has mesoderm lining the outside and endoderm on the inside. (coelomates have mesoderm lining the entire cavity)

37. What Is a Roundworm? • Roundworms are un-segmented worms that have pseudocoeloms and digestive systems with two openings—a mouth and an anus.

38. What Is a Roundworm? • This cavity is partially lined with tissue derived from the mesoderm and is called a pseudocoelom, meaning, “false coelom.”

39. What Is a Roundworm? • Roundworms have a digestive tract with two openings. • Food moves in one direction through the digestive tract of roundworms. • Any food that is not digested leaves the body through the anus.

40. Form and Function in Roundworms • Roundworms have specialized tissues and organ systems that carry out essential physiological functions.

41. Form and Function in Roundworms • Feeding • Many free-living roundworms use grasping mouthparts and spines to catch and eat other small animals.

42. Form and Function in Roundworms • Respiration, Circulation, and Excretion • Roundworms exchange gases and excrete metabolic waste through their body walls. • They depend on diffusion to carry nutrients and waste through their bodies.

43. Form and Function in Roundworms • Response • Roundworms have simple nervous systems, consisting of several ganglia. • Several nerves extend from ganglia in the head and run the length of the body. • These nerves transmit sensory information and control movement.

44. Form and Function in Roundworms • Movement • Fluid in the pseudocoelom and muscles extending the length of their bodies function as a hydrostatic skeleton. • Aquatic roundworms contract muscles to move like snakes through the water. • Soil-dwelling roundworms push their way through the soil by thrashing around.

45. Form and Function in Roundworms • Reproduction  • Roundworms reproduce sexually. • Most species have separate sexes. • Roundworms reproduce using internal fertilization. • Parasitic roundworms often have life cycles that involve two or three different hosts or several organs within a single host.

46. Roundworms and Human Disease • What roundworms cause human disease?

47. Roundworms and Human Disease • Parasitic roundworms include trichinosis-causing worms, filarial worms, ascarid worms, and hookworms.

48. Roundworms and Human Disease • Trichinosis-Causing Worms  • Adult Trichinella worms live and mate in the intestines of their hosts. • Female worms carrying fertilized eggs burrow into the intestinal wall and release larvae. • Larvae travel through the bloodstream and burrow into organs and tissues.

49. Roundworms and Human Disease • The larvae form cysts and become inactive in the host’s muscle tissue. • Trichinella completes its life cycle only when another animal eats muscle tissue containing these cysts. • Humans can get trichinosis by eating raw or incompletely cooked pork.

50. Roundworms and Human Disease • Filarial Worms  • Filarial worms are threadlike worms that live in the blood and lymph vessels of birds and mammals. • They are transmitted by biting insects. • Large numbers of filarial worms may block the passage of fluids within lymph vessels and cause swelling.