Phylum Cnidaria

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Phylum Cnidaria

• HW Study notes Define Vocab Words.

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Intro to Cnidarians

• How do you say it????
• Say it with me now (ni DARE ee uh)
• Practicing saying this when you are with your
  friends so you sound smart.
• What are cnidarians?
• Examples Jellyfish Sea Anemones
• Are there many species of cnidarians?
• Yes, there are 10,000 different species!

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Body Structure

• Like sponges, they have
• One body opening
• Two cell layers
• Unlike sponges
• Their cell layers are organized into tissues that
  have specific functions.
• They have symmetry

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Body Structure, contd

• The function of the two layers
• Outer Layer protects internal body
• Inner Layer mostly for digestion

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Cnidarian Symmetry

• Cnidarians are radially symmetrical.
• Remember what that means????
• Radially symmetrical organisms can detect
  capture prey from any direction.
• This is especially helpful for the sessile slow
  moving cnidarians.
• Some cnidarians are aquatic floaters.
• Others are sessile.
• Whats that again????

6
Feeding Digestion

• Whats a jellyfish look like?
• They have long, stinging
• tentacles.
• The tentacles have stinging cells
• called cnidocytes. (NI duh sites).
• They also have nematocysts.
• These are capsules that have
• threadlike tubes that contain
• poison barbs.

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The nifty nematocyst

• Nematocysts are like harpoons.
• They are propelled by osmotic pressure (water
  pressure).
• When a cnidarian is touched or otherwise
  stimulated water rushes into the nematocyst (by
  osmosis) and increases the water pressure,
  forcing the barb out of the nematocyst.
• The force is so strong that the barb can
  penetrate a crab shell.

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Feeding Digestion contd

• After prey is hit with a nematocysts or
  cnidocytes (tentacles) the cnidarian brings it to
  its mouth (its only opening).
• It then eventually makes its way to the
  gastrovascular cavity.
• Cells in the gastrovascular cavity secrete
  digestive enzymes to break down the captured
  prey.
• Any undigested material is then expelled through
  the mouth. Yummy.

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Response to stimuli

• Cnidarians have a primitive nervous system known
  as a nerve net.
• These specialized cells can cause contractions of
  muscle-like tissue.
• The movement of tentacles during prey capture is
  a result of these contractions.

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Types of organ systems

• As weve mentioned Cnidarians have
• A primitive digestive system
• A primitive nervous system
• They do not have
• A circulatory system
• A respiratory system
• Excretory system
• So while they are more complex than a sponge,
  they are still not very complex creatures.

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Comparison of Sponges Cnidarians
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Vocabulary Review -- HW

• Define the following words using your notes
• Radially Symmetry
• Sessile
• Cnidocyst
• Nematocyst
• Gastrovascular cavity
• Nerve net