Platyhelminthes

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Platyhelminthes
Phylum

• The Flatworms

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Flatworm Classification
Domain
Eukarya
Kingdom
Animalia
Phylum
Platyhelminthes
Class
Planarians -
Turbellaria
Flukes -
Trematoda
Tapeworms -
Cestoda
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ectoderm
endoderm
mesoderm
blastula
gastrula
gastrula
(2 germ layers)
(1 germ layer)
(3 germ layers)
Adult flatworms develop from the gastrula with an
ectoderm, endoderm, and mesoderm.
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Flatworms Have No Body Cavity
- body cavity is called a coelom - flatworms do
not have a coelom
flatworms are acoelomates
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Symmetry bilateral
anterior end
They have no bones they are invertebrates.
Hydrostatic pressure is used for support.
posterior end
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Flatworm Habitat
Whether a fluke, planarian, or tapeworm,
flatworms must live in a moist environment.
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Free-living flatworms (planarians) feed on dead
or very small live organisms.
Parasitic flatworms (flukes and tapeworms) live
inside other organisms.
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Free-living forms have a well-developed digestive
system.
Planarians eat detritus or small animals.
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Parasitic Flatworms
fluke
tapeworm
These flatworms lack a digestive system
nutrients diffuse from the host into the worm.
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All flatworms use simple diffusion to get O2 and
get rid of CO2 they lack respiratory and
circulatory structures.
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Class Turbellaria free-living planarians
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Ocean Turbellarians
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Planarian Nervous System
nerves that detect touch
eyespots
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eyespots
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Planarian Excretory System
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Planarians Move Using Cilia and Muscles
muscles
cilia
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Movement with Muscles
Muscles can be used to cause the sides to ripple
allowing the flatworm to swim.
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Planarians Are Hermaphrodites
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Fission in Planarians
- planarians can reproduce asexually
by splitting in two
Both halves will regenerate the missing parts.
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Planarians Can Regenerate
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Class Trematoda parasitic flukes
Digenea in kidney
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An eye with Digenea
retina
Digenea
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Adult Liver Fluke
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Schistosoma
suckers
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Schistosomiasis
one species of Schistosoma invades the liver
the disease is called schistosomiasis
Schistosoma
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Class Cestoda parasitic tapeworms
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Tapeworm from a Fish
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scolex (head)- with hooks
scolex- with suckers
and suckers
suckers
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body sections are called proglottids each is a
reproductive structure
they are hermaphrodites
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scolex
proglottids
eggs
Small Tapeworm
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Proglottids showing reproductive structures
testes
ovaries
testes
ovaries
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Example of a Tapeworms Life Cycle
eggs released in feces
1.
4.
2.
3.