Worms

Flatworms• Bilateral symmetry• No coelum• Has organs & systems• 3 body layers

– Ectoderm– Mesoderm– Endoderm

• Gasses pass in/out by diffusion• Anterior end w/ mouth• Primitive brain

Flatworm Reproduction• Asexual

– Stretch or break apart– Each half becomes new

animal

• Sexual– Hermaphrodites– Both transfer sperm to one

another

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Flatworm Parasites• Tapeworms

– Larvae enter through undercooked meat

– Hooks attach to inner walls of intestines

– Food absorbed through skin

– Grow up to 12 meters

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