Phylum Platyhelminthes
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Phylum Platyhelminthes
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Flatworms
Triploblastic
Acoelomate
Bilateral symmetry
Hermaphroditic (Most)
– Monoecious
• One opening for digestive
system - incomplete gut
• Paired lateral nerve
cords & cerebral ganglion
• Flame cells - modified
excretory cells
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Acoelomate
Ectoderm
Mesoderm
Endoderm
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Nervous System
Lateral nerve cord
Cerebral ganglion
Connectives
Eye spot
Auricle
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Excretory System
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Class Turbellaria
• Eye spots - Ocelli
• Ciliated surface
• Dual Adhesion Glands to attach and release
• Regenerate if cut
• Most are free-living
• Detect food by
chemoreceptors
• Detect Water Current statocysts
• Sexual Reproduction:
– Internal Fertilization
– Cocoon attached to plants
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Releasing and Attaching (Viscid) Glands
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Turbellaria
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Class Trematoda
• Flukes
• Parasites - endoparasitic
• Holdfast devices
– Hooks and Suckers
• Complex life cycle
• Intermediate host
– Animal with juvenile stage
• Definitive host
– Animal with adult stage
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Chinese liver fluke
50 million people
Cirrhosis of liver
Diarrhea
Pain
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General
Trematoda (FLUKE) Life Cycle
Egg
passes from definitive host and must
reach water
Hatches into a free-swimming ciliated
larva, the miracidium
Miracidium penetrates tissues of a snail
Transforms
Sporocyst
into a sporocyst
reproduces asexually to form
redia
Rediae reproduce asexually and form
cercaria
Cercaria attach to fish and form cysts in
muscle tissue
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• Sheep liver fluke
• Sheep, cattle and
man
– Weight loss
• Eat vegetation with
metacercaria
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Intestinal fluke
10 million people
Man and pigs
Hemorrhage and
abscesses of small
intestine
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• Lung fluke
• Carnivores, pigs,
rodents and man
• May be fatal
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Lung Fluke Distribution
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Schistosoma
• Blood flukes/Liver
• 200 million people
infected
• 1 million deaths/year
• Sexes are separate
• Pierce through Skin
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Life Cycle of a Schistosome Fluke
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Cut Liver of individual who dies from hematemesis
(vomiting blood). 180 adult blood flukes were found in autopsy
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Schistosome
• Swimmers Itch Schistosoma
Dermatitis
– Cercaria penetrate
wrong host
– skin becomes irritated
and inflammed = itch
Cercaria have forked tail
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Swimmers Itch
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Class Cestoidea
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Tape worms
No digestive system
40 feet long
Individual units =
proglottids
– Contain own reproductive
structures and organs
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Scolex
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Proglottid
Testes
Uterus
Vas deferens
Seminal receptacle
Ovary
Yolk gland
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Pork Tapeworm (Taenia solium)
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Taenia
saginata
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