4/18/2012
What is a flatworm?
Flatworms
Acoelomates
Thin, solid bodies
Can be 1mm to several meters
14,500 species
Marine and freshwater and moist
habitats on land
3 true cell layers: endoderm,
ectoderm & mesoderm
Ex. Tapeworms, flukes,
planarians
Nervous System
Some have a nerve net, others have a primitive central
nervous system
Ganglia concentrated in the cephalic area
Cephalization: nerve cells concentrated in the head region
Enables flatworms to respond to stimuli
Ex. Planaria
Two nerve cords that run the length of the body
Eyespots that detect the presence or absence of light
Sensory cells that detect chemicals and movements in water
Ganglion at the anterior end – receives messages from the
eyespots and sensory pits and communicates with the rest of
the body along the nerve cords
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Feeding and
Digestion
Reproductive System
Hermaphrodites
Sexual reproduction:
Asexual reproduction:
ability to regenerate new body parts through
cell divisions
If cut horizontally, each half will grow a new
tail/head
Tapeworm
Structure Function
Extends a tube-like, muscular organ called the pharynx
Enzymes released by the pharynx begin digesting food
outside of the body
Food particles are sucked into the digestive tract
Cells lining the digestive tract obtain food by endocytosis
Food is digested in individual cells
Parasitic flatworms obtain food from inside the bodies of a
host
Have mouthparts with hooks
Do not have complex nervous or muscular tissue (don’t need
to move)
Beef Tapeworm Life Cycle
a section of the tapeworm body
Contains male and female reproductive
organs
Able to self- or cross-fertilize
The Proglottids at the end of the body break
off and pass out in feces of host
Each Proglottids contains many fertilized
eggs
Head:
Proglottids:
Planarians feed on dead or slow-moving organisms
Individual planarians exchange sperm
Fertilization occurs internally
Zygotes are released in capsules into the
water where they hatch into tiny planarians
has hooks and four suckers for attachment
to gut wall
New Proglottids formed from the head
Cuticle:
Protective outer covering to avoid being
digested by host enzymes
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Fish Tapeworm Lifecycle
Pork Tapeworm Lifecycle
Schistosomiasis
Life Cycle
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