Phylum Platyhelminthes

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Phylum Platyhelminthes

• The Flatworms

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Phylum Platyhelminthes
Examples include Planaria Tapeworms Flukes Polycl
ad flatworms
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Characteristics

• Bilateral symmetry
• Flattened bodies
• 12,000 species
• 1 mm to 10 m
• Most aquatic or parasitic
• External suckers or hooks

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More Characteristics

• No coelom
• Digestive tube with mouth, anus, and intestine.
• Food in through mouth, undigested food leaves
  through pharynx

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Muscles are both longitudinal and circular
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Classification
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Class Turbellaria

• Planaria
• Polyclad flatworms (marine)
• Creeping motion achieved through muscles and
  cilia
• Only class containing free living worms

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Class Trematoda

• All parasitic flukes
• Infect vertebrates, including humans
• Leaflike form
• Hooks or suckers
• Liver fluke, blood fluke, lung flukes, swimmers
  itch

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Class Monogenea

• Parasitic flukes, primarily on gills or external
  features of fish
• Direct life cycle, with a single host

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Class Cestoda

• Tapeworms
• Internal parasites of vertebrates, including
  humans
• Holdfast called scolex
• 1000 species
• Life cycle requires two hosts

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