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Worms Flatworms • • • • Bilateral symmetry No coelum Has organs & systems 3 body layers – Ectoderm – Mesoderm – Endoderm • Gasses pass in/out by diffusion • Anterior end (front) w/ mouth • Primitive brain Flatworm Reproduction • Asexual – Stretch are break apart – Each half becomes new animal • Sexual – Hermaphrodites – Both transfer sperm to one another Web link Flatworm Parasites • Tapeworms – Larvae enter through undercooked meat – Hooks attach to inner walls of intestines – Food absorbed through skin – Grow up to 12 meters • Flukes – Internal or external parasites – Contain protective layer to prevent from being digested – Ex: Schistosomiasis One Final Look Roundworms • Cylindrical bodies w/ mouth and anus • Separate male/female – Sexual reproduction • 1st to have body cavity (coelum) – Movement of fluid circulates gas & nutrients • Most small in size (few mm) • Most free-living Roundworm Parasites • Ascaris – Infects pigs, horses, humans – Knots of worms can block intestines (cause death) – Larvae cause respiratory illness – Females: lay 200,000 eggs/day • Trichinella – Eat undercooked pork – Larvae burrow into intestines & mature – New larvae pass into blood & form cysts in muscles Segmented Worms • Have coelum • Several organ systems – Complex digestive system – Circulatory sys: 2 blood vessels – Nervous sys: Primitive brain and nerve cord – Muscular sys: Circular & longitudinal muscles • Gas exchange through skin Segmented Worm Reproduction • Hermaphroditic • Ventral surfaces press together – Mucus holds worms together • Sperm released into the mucus & stored in a pouch • Worms develop inside pouch Segmented Leeches • Live in calm, freshwater • Sucker attached to host or prey • Release anaesthetic to hide presence • Can eat up to 10x own weight • Used to help restore blood flow in limb reattachment
