Platyhelminthes

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Platyhelminthes

• Usually flattened dorsoventrally
• Triploblastic
• Acoelomate
• Bilaterally symmetrical
• Unsegmented worms
• Incomplete gut (absent in tapeworms)
• Somewhat cephalized, with anterior

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• Cerebral ganglion (brain) and longitudinal
  nerve cords
• Protonephridia (excretory structures)
• Hermaphroditic

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ClassTurbellaria

• Free-living predators and scavengers
• Freshwater marine
• Crawl on stones, sand or vegetation
• Most less than 1 cm long
• Ex. Planaria

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• Body wall
• Some ciliated
• Circular and longitudinal muscles
• Gastrodermal cells comprise digestive
  cavity-secrete enzymes that aid in digestion

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• Locomotion
• 1st group of bilaterally symmetrical animals
• Glide using cilia and muscular undulations
• Secrete mucus that aids in adhesion and helps
  cilia gain traction

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• Digestion and Nutrition
• Digestive cavities vary from unbranched chamber
  to highly branched digestive tubes
• Pharynx-tubelike for ingesting food can project
  out of mouth when feeding
• Carnivores and herbivores
• Digestion is partially extracellular-enzymes
  break down food into smaller particles and
  digestion is completed in intracellular vesicles

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• Exchanges with the environment
• Gases exchanged by diffusion through body wall
• Wastes (ammonia) removed by diffusion
• Protonephridia-fine tubules that run the length
  of the body
• Side branches of the tubules have flame cells
  with cilia that drives fluid down through the
  tubule and to the outside of the body through
  nephridiopores.

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