1. Figure 33.9x A flatworm

2. Figure 33.10 Anatomy of a planarian

3. General Characteristics They exhibit bilateral symmetry: anterior and posterior ends are different; so are the dorsal (top) and ventral (bottom) surfaces The platyhelminths also exhibit some degree of cephalization They are acoelomates

4. Outer Body Covering The body of some platyhelminthes (e.g., turbellarians) is covered by a ciliated epidermis Epidermal cells contain rod-shaped cells that expand and form a protective mucous coat around the animal The outer body covering of other platyhelminthes (e.g., parasitic forms) is a non- ciliated tegument

5. Organ Systems of the Platyhelminthes Digestive System Some of the flatworms possess a digestive system, with a mouth, pharynx, and a branching intestine from which the nutrients are absorbed

6. Excretory System (osmoregulation) A network of water collecting tubules adjacent to flame cells or protonephridia When cilia beat they move water into the tubules and out the body through pores called nephridiopores

7. Muscular System Below the epidermis are layers of circular and longitudinal muscle fibers; used in locomotion Nervous System Includes: anterior cerebral ganglia, longitudinal nerve cords, and some lateral nerves Most free living planarians and parasitic larval forms possess a variety of sensory organs

8. Reproductive System Most are capable of some form of asexual reproduction (e.g., many turbellarians reproduce by fission) Most flatworms are hermaphroditic; however, they often pair with other individuals to exchange gametes

10. Table 33.2 Classes of Phylum Platyhelminthes

11. Locomotion Most move by means of cilia and mucous Muscle contractions also permit turning, twisting, and folding Class Turbellaria Free-living flatworms; mostly marine organisms Range in size from microscopic (interstitial species between sand grains) to about 2 feet.

12. Nutrition Turbellarians are carnivores and prey on other animals or eat dead animal remains. Planarians have a muscular pharynx that they can insert into their prey and then pump to bring in food fragments These animals have a highly divided gut to greatly increase the surface area for digestion and absorption Senses They have well developed sensory structures, including eyespots, mechanoreceptors, and chemoreceptors

13. Class Trematoda Flukes that live as parasites either on or in other organisms;outer body lacks cilia. Possess 2 suckers: 1. Oral sucker which attaches to organs of the host 2. Ventral sucker used to attach to host tissues

14. Figure 33.11 The life history of a blood fluke, Schistosoma mansoni

16. Figure 33.12 Anatomy of a tapeworm

17. Class Cestoda The scolex includes hooks and suckers. Extending from the neck is a series of proglottids, contain the sex organs and eggs; no digestive system Mature eggs released through an opening in the proglottid or leave the host when the proglottids are separated from the main body of the worm.

18. Taenia

19. Proglottids Uterus Testes