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

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

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