Phylum: Cnidarians

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Phylum Cnidarians
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What is a Cnidarian?

• A cnidarian is an invertebrate
• It uses stinging cells to capture prey
• Examples
• Jellyfish
• Corals
• Sea Anemones

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Body Structure

• All cnidarians have the following
  characteristics
• Radial symmetry
• A hollow central cavity
• Tentacles with stinging cells
• However, cnidarians can have one of 2 different
  body plans.
• Polyp
• Medusa

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Body Plans

• Polyp
• Mouth opens at top
• Vase-shaped
• Attached to a surface
• Examples Hydra, Sea anemone, Coral

• Medusa
• Mouth opens down
• Tentacles point down
• Adapted for a swimming life
• Examples Jellyfish

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Activity Color Code a Cnidarian
Endoderm
Tentacle
Jelly-like layer (Mesoglea)
Ectoderm
Tentacle
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Obtaining Food

• Stinging cells inject venom which paralyzes the
  prey
• THINK! Why are clown fish resistant to the
  toxins given off by sea anemones?
• Tentacles pull the prey into the mouth
• Digestion happens in the body cavity
• Waste is expelled back out through the mouth

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Movement

• Cnidarian movements are directed by nerve cells
  that spread throughout the cnidarians body like a
  basketball net
• Jellyfish swim through water
• Hydras can be found in freshwater and turn
  somersaults or use their tentacles to move
• Watch these Hydra Movies
• http//micro.magnet.fsu.edu/optics/olympusmicd/gal
  leries/moviegallery/pondscum/coelenterata/hydra/in
  dex.html
• Sea anemones stretch out, shrink down, and bend
  slowly from side to side

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Reproduction

• Asexual
• Budding is most common in hydras, corals, sea
  anemones where these polyps just pull apart
  forming two new polyps.
• Sexual
• Can occur during the life cycle of certain
  cnidarians such as the jellyfish

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Life Cycle of A Jelly Fish
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Life on a Coral Reef

• Coral polyps produce a hard, stony skeleton
  around its soft body once attached to a hard
  surface.
• Coral polyps then continue to reproduce asexually
• Over time, reefs build up from the sea floor and
  make great homes for other sea life

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Video Quiz

• Watch the following clip
• Coral Ecosystems (559)
• There will be a short video quiz following the
  clip.
• Make sure to take good notes! You can use your
  notes for the video quiz!