Phylum Nemertea

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Phylum Nemertea Phylum Chaetognatha

• Ribbon Worms
• Arrow Worms

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Phylum Nemertea

• Long, slender, soft unsegmented worms with an
  eversible proboscis

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The Proboscis
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Digestion and Circulatory Systems

• Lacks an exoskeleton skin is densely ciliated
  which circulates water for gas exchange
• Eyespots are located on the head near the brain
• Food is digested rapidly and processed in a
  linear digestive tract

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Reproduction

• Sexes are separate with fertilization occurring
  in the water column
• Usually solitary animals that aggregate at
  spawning
• Long lived free-swimming larvae pilidium
• Great powers of regeneration

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Local Representatives

• Milky ribbon worm (Cerebratulus lacteus)

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Phylum Chaetognatha (Arrow Worms)

• Defining Characteristics
• A series of curved chitinous grasping spines on
  both sides of the head, for seizing prey
• Lateral stabilizing fins

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Chaetognaths Habits

• Living Chaetognaths are almost invisible in the
  water
• Possess two eyes that are useful for sensing
  motion and light intensity

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Chaetognatha Feeding

• A prey item is sensed by cilia along the body
• Feed on copepods, larval crustaceans, young fish
  and each other
• Can occur in very high concentrations several
  hundred per cubic meter
• Can have substantial effects on eggs and larvae
  some of which are commercially important

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Reproduction