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Worms
Flatworms
• Bilateral symmetry
– Anterior end (front) w/
mouth
• Have organs &
systems
– Primitive brain
– Pharynx extends from
mouth to feed
• 3 body layers
– Ectoderm
– Mesoderm
– Endoderm
• Gasses pass in/out
by diffusion
Flatworm Reproduction
• Asexual
– Stretch and break
apart
– Each piece
becomes new
worm
– Regeneration
• Sexual
– Hermaphrodites
– Both transfer
sperm to one
another
Flatworm Parasites
Eggs in human tissue
• Tapeworms
– Larvae enter
through
undercooked meat
– Hooks attach to wall
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)
• Some free-living; Many parasites
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 (Annelids)
• 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
• Eat organic waste
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