Phylum Platyhelmenthes Planarians, Flukes,

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Phylum PlatyhelmenthesPlanarians, Flukes,
Tapeworms

• Simple acoeleomates
• Bilaterally symmetrical
• Most flattened "Dorsoventrally"
• Divided into 4 classes

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Class Turbellaria

• Most free-living and non parasitic
• Include planarians
• Lack circulatory and gas-exchange organs.
• Simple excretory structures called flame cells
  that maintain osmotic balance.
• Is cephalized and has eye-spots which are
  sensitive to light
• Feeds through ventral feeding tube called a
  pharanx
• Can reproduce sexually, or asexually through
  regeneration

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Planarian and assorted marine flatworms
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Class Trematoda (Flukes)

• Similar in form to turbillarians
• Many are parasitic. Example of parasitic fluke is
  the asian liver fluke
• Many have complex life cycles including multiple
  hosts and alternation of generations.

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Life Cycle of the Liver Fluke
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Liver Flukes Contd
Liver Fluke
Liver Fluke encysted in a liver
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Class Cestoda (Tapeworms)

• Parasitic flatworms
• Can grow to enormous lengths (up to 20m)
• Parasitize mostly vertebrate hosts
• Attach head named scolex to intestinal walls of
  host, and abosrb host's nutrients
• Following scolex is a series of repeating
  structural units called proglottids
• Mature proglottids containing thousands of eggs
  are released with the host's feces to infect
  other organisms.

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Tapeworms contd