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Phylum Platyhelminthes

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Phylum Platyhelminthes• 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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AcoelomateAcoelomate

EctodermEctodermMesodermMesodermEndodermEndoderm

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Nervous System

Lateral nerve cordLateral nerve cord

ConnectivesConnectives

AuricleAuricleEye spotEye spot

Cerebral ganglionCerebral ganglion

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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 General Trematoda (FLUKE) Life Cycle Egg passes from definitive host and must Egg passes from definitive host and must reach waterreach waterHatches into a free-swimming ciliated Hatches into a free-swimming ciliated larva, the larva, the miracidiummiracidiumMiracidium penetrates tissues of a snailMiracidium penetrates tissues of a snail

Transforms into a Transforms into a sporocystsporocystSporocyst reproduces asexually to form Sporocyst reproduces asexually to form rediarediaRediae reproduce asexually and form Rediae reproduce asexually and form cercariacercariaCercaria attach to fish and form cysts in Cercaria attach to fish and form cysts in muscle tissuemuscle 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

• 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

UterusUterus

TestesTestes

OvaryOvary

Yolk glandYolk gland

Vas deferensVas deferens

Seminal receptacleSeminal receptacle

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Pork Tapeworm (Taenia solium)

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Taenia saginata

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