Ch' 36 Platyhelminthes phylum

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Ch. 36 Platyhelminthes (phylum)

• Flatworms
• Lacks circulatory system
• Lacks respiratory system
• Bilateral symmetry
• Senses and nerves at the anterior end called
  cephalization.
• Three classes Turbellaria, Trematodes, Cestoda.

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Turbellaria (class)

• Planaria is an organism in this class.
• 1. Its freshwater
• 2. Swims with the aid of cilia
• 3. Its mouth is in the middle of its body. It
  extents out by a tube called the pharynx.
• 4. Water and wastes are exited out the planaria
  through the flame cells.

3

• 5. Planaria have the ability to sense light with
  2 anterior eyespots.
• 6. Planaria have 2 anterior nerve cells called
  ganglia. The ganglia enables the planaria to
  sense touch, taste, and smell. It is much like a
  simple brain.
• 7. Planaria are hermaphrodites.
• 8. Planaria are able to regenerate.

4
Trematoda (class)

• Flukes (hosts)
• Endoparasites live inside the host
• Ectoparasites live on the external surface of
  the host.

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• Lifecycle of the liver fluke
• Mates inside the liver of a sheep. Eggs enter the
  intestine and exit. Eggs hatch in water and
  invade snails as larva form. The larva leave the
  snails as a free swimmer and form a cyst on grass
  blades on land. The sheep eat the grass and the
  cyst hatches in the digestive tract and bore
  there way into the blood system which leads them
  to the liver.

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Cestoda (class)

• Tapeworms
• 1. Parasitic just like flukes.
• 2. Lack sense organs, mouth, and digestive system
• 3. Attaches to a host with its hooks and suckers.
• 4. Head is called scolex. Body segments are
  called proglottids.

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Nematoda (phylum)

• Roundworms
• 1 mm to 120 cm
• Parasites in digestive tract
• 2 openings mouth and anus
• Trichinosis occurs in humans. Become infected by
  eating undercooked pork with trichina cysts.
  Causes pain and stiffness as a cyst in muscle
  cells.
• Freeze pork for 72 hours.