3. Flatworms  Phylum Platyhelminthes  Are soft, flattened worms  Have tissues and an internal organ system  They are the simplest organisms to have three embryonic germ layers.  Bilateral symmetry  Exhibit cephalization  Acoelomates

5. Planaria

8. Flatworms  Rely on diffusion for essential body functions like respiration, excretion, and circulation They have a digestive cavity with a single opening, or mouth They have a digestive cavity with a single opening, or mouth Food enters a flatworms body cavity through a muscular tube called a pharynx Food enters a flatworms body cavity through a muscular tube called a pharynx Most parasitic flatworms don’t need complex digestive systems because the obtain nutrients from food already digested by their host Most parasitic flatworms don’t need complex digestive systems because the obtain nutrients from food already digested by their host Many flatworms can detect changes in the amount of light in their environment using groups of cells called eyespots Many flatworms can detect changes in the amount of light in their environment using groups of cells called eyespots

9. Classes of Flatworms  Tubullarians Plananria Plananria Live in fresh water and marine environments. Live in fresh water and marine environments. Free living Free living  Tremetoda Parasitic flatworms Parasitic flatworms Flukes Flukes Found in tropical areas with improper sewage Found in tropical areas with improper sewage Causes Schistosomiasis Causes Schistosomiasis  Cestoda Tapeworms Tapeworms Live in mammalian intestines Live in mammalian intestines

10. Flatworms  Types of flatworms include: Turbellarian Turbellarian free-living and live in marine or freshwaterfree-living and live in marine or freshwater Flukes are parasites that infect the internal organs of their host Flukes are parasites that infect the internal organs of their host Reproduce sexually in primary hostReproduce sexually in primary host Reproduce asexually in intermediate hostReproduce asexually in intermediate host Tapeworms are long flat worms that live in intestines Tapeworms are long flat worms that live in intestines In tapeworms, both male and female reproductive organs are contained in each mature proglottid (the segments that make-up the worm’s body)In tapeworms, both male and female reproductive organs are contained in each mature proglottid (the segments that make-up the worm’s body)