Unit 8 Chapter 27 Mollusks and Segmented Worms

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Unit 8Chapter 27Mollusks and Segmented Worms
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What is a Mollusk?

• Bilateraly symmetry, coelomates, and
  well-developed body systems
• Soft bodies covered by a thin mantle, which may
  secrete a shell

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What is a Mollusk?

• Mollusks have a foot,
  a ventral structure
  for locomotion
• Some have an open circulatory system, blood moves
  through vessels into open spaces around body
  organs
• Others have a closed circulatory system, blood
  moves through the body enclosed entirely in blood
  vessels

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What is a Mollusk?

• Gastropods include snails and slugs
• One shell, belly-footed
• Radula scraping tongue-like structure

Radula magnified 1000X
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What is a Mollusk?

• Bivalves include clams, oysters muscles
• Two shells,
  hatchet-footed
• Filter-feeders

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What is a Mollusk?

• Cephalopods include octopus, squid, cuttlefish,
  chambered nautilus
• Little or no shell,
  foot divided into
  tentacles with suckers
• Use ink and jet propulsion
  to escape from danger

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What is a segmented worm?

• Phylum Annelida
• Bilaterally symmetrical, segmented coelomates,
  with two body openings

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What is a segmented worm?

• Earthworms have complex body systems
• Digestive system includes a crop gizzard for
  grinding food taken from soil
• Closed circulatory system includes 5 pair of
  hearts
• Reproductive system includes both ovaries testes

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What is a segmented worm?

• Leeches are freshwater,
  external parasites
• Some microsurgeons use leeches after surgery to
  improve blood flow

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What is a segmented worm?

• Marine worms include bristle worms, fan worms and
  tube worms (below)
• Most have structures for swimming or crawling on
  the bottom of the sea