1. Phylum Platyhelminthes (flatworms) • 18,500 spp. • most primitive bilateral animals • acoelomate • triploblastic • minimal cephalization • no circulatory system • nervous system- ladder-like

2. Taxonomy • Class Turbellaria (planarians) • Class Trematoda (flukes) • Class Cestoda (tapeworms)

3. Flatworm Physiology • Respiration and excretion via diffusion through the body wall • hermaphroditic w/ internal fertilization • asexual reproduction via fragmentation

4. fresh water, terrestrial, mostly marine ciliated epidermis evertable pharynx example: Planaria Class Turbellaria (planarians)

6. 11,000 spp. medically important endoparasites of vertebrates eggs void in feces free swimming larvae example: Clonorchis Chinese liver fluke Class Trematoda (flukes)

8. 3400 spp. endoparasites of vertebrates scolex- holdfast proglottids example: Taenia- beef tapeworm Class Cestoda (tapeworms)