Platyhelminthes (Flatworms) and Nematoda (Roundworms)

1. Platyhelminthes (Flatworms) and Nematoda (Roundworms)

2. Section 26.3 Summary– pages 706-710 Platyhelminthes (Flatworms) • Flatworms are the least complex worms • acoelomates with thin, solid bodies. Planarian

3. Section 26.3 Summary– pages 706-710 Platyhelminthes (Flatworms) • approximately 14,500 marine and freshwater species of flatworms • They are found in bodies of water and moist habitats Planarian

4. Section 26.3 Summary– pages 706-710 Platyhelminthes (Flatworms) • The most well-known members are the parasitic tapeworms and flukes, which cause diseases in other animals • The most commonly studied flatworms are the free-living planarians Free living = not parasitic

5. Section 26.3 Summary– pages 706-710 Planarians • Planarians have many characteristics common to all species of flatworms. • The bodies are flat, with a dorsal and a ventral surface. All flatworms have bilateral symmetry. Dorsal = Top Ventral = Bottom

6. Section 26.3 Summary– pages 706-710 Planarians • Most of the nervous system is located in the head—a characteristic common to other bilaterally symmetrical animals. Nerve cell mass

7. Section 26.3 Summary– pages 706-710 Planarians • Some flatworms have a nerve net, and others have the beginnings of a central nervous system. Nerve cell mass Nerve cord • Planarians have two nerve cords that run the length of the body.

8. Section 26.3 Summary– pages 706-710 Planarians • Nervous system includes eyespots that can detect the presence or absence of light and sensory cells that can detect chemicals and movement in water. Eyespots

9. Section 26.3 Summary– pages 706-710 Planarians • At the anterior end of the nerve cord is a ganglion (plural, ganglia). The ganglion receives messages from the eyespots and sensory pits, then communicates with the rest of the body along the nerve cords. Ganglia • Messages from the nerve cords trigger responses in a planarian’s muscle cells.

10. Section 26.3 Summary– pages 706-710 Reproduction in Planarians • Most flatworms including planarians, are hermaphrodites. • During sexual reproduction, individual planarians exchange sperm, which travel along special tubes to reach the eggs. • Fertilization occurs internally. Zygotes are released in capsules into the water, where they hatch into tiny planarians.

11. Section 26.3 Summary– pages 706-710 Reproduction in Planarians • Planarians also can reproduce asexually. • When a planarian is damaged, it has the ability to regenerate. • If a planarian is cut horizontally, the section containing the head regenerate a new tail, and the tail section will regenerate a new head.

12. Section 26.3 Summary– pages 706-710 Feeding and Digestion • Planarians feed on dead or slow-moving organisms. • It extends a tube-like, muscular organ, called the pharynx (FAHR inx), out of its mouth. Enzymes released by the pharynx begin digesting food outside the animal’s body. Extended pharynx

13. Section 26.3 Summary– pages 706-710 Feeding and Digestion • Food particles are sucked into the digestive tract, where they are broken up. • Cells lining the digestive tract obtain food by endocytosis. • Food is thus digested in individual cells.

14. Section 26.3 Summary– pages 706-710 Parasitic Flatworms • Parasite = an organism that lives on or in another organism and depends upon that host organism for its food.

15. Section 26.3 Summary– pages 706-710 Parasitic Flatworms • Parasitic flatworms have mouthparts with hooks that keep the flatworm firmly attached inside its host. • They do not need to move to seek out or find food. • Parasitic flatworms do not have complex nervous or muscular tissue. Parasitic flatworms make up two classes, Tapeworms and Parasitic Flukes

16. Section 26.3 Summary– pages 706-710 Tapeworms Hooks • knob-shaped head called a scolex and detachable, individual sections called proglottids. Scolex Sucker Proglottid • Proglottids contain muscles, nerves, flame cells, and male and female reproductive organs. Mature proglottid with fertilized eggs • Some adult tapeworms that live in animal intestines can be more than 10 m in length and consist of 2000 proglottids.

17. Section 26.3 Summary– pages 706-710 Flukes • A fluke is a parasitic flatworm that spends part of its life in the internal organs of a vertebrate, such as a human or sheep. • It obtains its nutrition by feeding on cells, blood, and other fluids of the host organism.

18. Section 26.3 Summary– pages 706-710 Flukes • Blood flukes of the genus Schistosoma cause a disease in humans known as schistosomiasis. • Schistosomiasis is common in countries where rice is grown. • Blood flukes are common where the secondary host, snails, also are found.

19. Section 26.3 Summary– pages 706-710 The life cycle of a fluke Adult flukes Larva Embryos released Human host Snail host Larva

20. Section 26.4 Summary– pages 711-713 Nematoda (Roundworms) • widely distributed, living in soil, animals, and both freshwater and marine environments. • Most are free-living, but many are parasitic. Roundworm

21. Section 26.4 Summary– pages 711-713 Nematoda (Roundworms) • tapered at both ends. • thick outer covering protects them in harsh environments. Covering is shed 4 times as they grow. Tapered ends Round body shape

22. Section 26.4 Summary– pages 711-713 Nematoda (Roundworms) • No circular muscles, but have lengthwise muscles. • One muscle contracts, another muscle relaxes. This alternation causes roundworms to move in a thrashing fashion.

23. Section 26.4 Summary– pages 711-713 Nematoda (Roundworms) • Have a pseudocoelom and are the simplest animals with a tubelike digestive system. • Roundworms have two body openings—a mouth and an anus! This is a first for us! Intestine Anus Mouth Round body shape

24. Section 26.4 Summary– pages 711-713 Nematoda (Roundworms) • Eyespots are reduced in parasitic roundworms. • Approximately half of roundworm species are parasites, and about 50 species infect humans. Examples: Ascaris, Pinworms, Trichenella, and Hookworms

25. Ascaris Section 26.4 Summary– pages 711-713 • the most common roundworm infection in humans • Children infected more often than adults • Eggs are found in soil and enter a human through the mouth. • Eggs hatch in the intestines, move into the bloodstream, and eventually to the lungs, where they are coughed up, swallowed, and begin the cycle again.

26. Pinworms Section 26.4 Summary– pages 711-713 Pinworms are the most common human roundworm parasites in the United States. • highly contagious because eggs can survive for up to two weeks on surfaces. • live eggs are ingested and mature in the host’s intestinal tract. • female pinworms exit the host’s anus and lay eggs on nearby skin. • eggs fall onto bedding or other surfaces.

27. Trichinella Section 26.4 Summary– pages 711-713 • Trichinella causes a disease called trichinosis(tri keh NOH sis). • Found in raw or undercooked pork, pork products, or wild game. Trichinella

28. Hookworms Section 26.4 Summary– pages 711-713 • Hookworm infections are common in humans in warm climates where they walk on contaminated soil in bare feet. • Hookworms cause people to feel weak and tired due to blood loss.

29. Roundworm Parasites Section 26.4 Summary– pages 711-713 • Nematodes can infect and kill pine trees, cereal crops, and food plants such as potatoes. • They are particularly attracted to plant roots and cause a slow decline of the plant. • They also can infect fungi and can form symbiotic associations with bacteria. • Nematodes also can be used to control pests.