Cnidarians Coelenterates

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Cnidarians Coelenterates

• -The name Cnidaria comes from the Greek word
  "cnidos," which means stinging nettle.
• Have radial symmetry
• -Have stinging cells called nematocysts
• -Nematocysts eject barbed threads tipped with
  poison.
• -Many thousands of cnidarian species live in the
  world's oceans, from the tropics to the poles,
  from the surface to the bottom. Some even burrow.
  A smaller number of species are found in rivers
  and fresh water lakes.

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Basic Body Parts

• Some Cnidarians exist only as polyps, such as sea
  anemones and corals.
• And other exist as both polyp and medusa
  depending on the stage of their life cycle.
  These are your hydroids and jellyfish.

medusa
Polyp
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• Polyps are attached to a sub-straight (something
  on the bottom).
• Medusa are free floating or swimming animals.
• In both forms the wall of the body tube consists
  of just 2 layers of cells an outer epidermis and
  an inner gastrodermis separated by a jellylike
  matrix, called the mesoglea.
• The central cavity of the tub acts as a gut
  having only one opening, allowing both food to
  enter and waste to be expelled.

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Polyp Body Parts

• The mouth of the polyp faces outward. At the
  opposite end of the body is a basal disk, which
  is often attached to a solid surface.
• Spreading out from the mouth are the tentacles.

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Medusa Body Parts

• The body of a medusa looks like a bell, with the
  mouth at the center of the lower surface and
  tentacles at the edges.
• The mesoglea, (The layer between the inside and
  the outside skin of the jellyfish.) is thicker
  here then in most polyps. Some medusa have a
  shelf of tissue that is rich in muscle cells and
  used in locomotion.

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Tentacles Nematocysts

• Tentacles extend from the outer edges of the bell
  of a medusa or the basal disk of a polyp.
• Tentacles aid in the collection of prey for food.
• Because tentacles tend to be very fragile, the
  jellyfish needs to have a way of stopping the
  prey from ripping off the tentacles. This bring
  us to the Nematocysts.

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Nematocysts

• A nematocyst or stinging cell, is a coiled,
  barbed thread. When triggered by touch, the
  threat explodes outward and pierces the victims
  skin. The tentacles are then used to pull the
  prey in.
• All Cnidarians have nematocysts and therefore all
  Cnidarians have the capability of stinging you.
  However, only about 70 or so of the 2700 species
  of Cnidarians nematocysts can penetrate your
  skin. So they all sting you, you just cant feel
  most of them.

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There are four major groups of cnidarians

• Anthozoa, which includes true corals, anemones,
  and sea pens
• Sea Anemones and Corals
• In this photo there are not only soft coral, but
  precious black coral, elkhorn coral,
• and a giant clam.

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Cubozoa, the amazing box jellies with complex
eyes and potent toxins
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Hydrozoa, the most diverse group with
siphonophores, hydroids, fire corals, and many
medusae
With 2700 speciesTypical hydroids pass through
both polyp and medusa phases in their life cycle,
but some species only live as polyps. Hydroids
are small, inconspicuous creatures, measuring
only a fraction of an inch, and much of the
marine growth on rocks and shells is produced by
hydroid polyps.
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Scyphozoa, the true jellyfish.
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Chrysaora sp. from the Pacific. These species can
grow up to a meter in diameter.
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• Life Cycle of a Jellyfish
• In the reproductive life cycle of a typical
  jellyfish, males release sperm and females
  release eggs into the water. When an egg and
  sperm fuse to form a fertilized egg during sexual
  reproduction, a larva develops that attaches to a
  rock or other object and develops into a polyp.
  In a type of asexual reproduction, the polyp
  transforms into a colony of polyps that resembles
  a stack of saucers. Each saucer in the stack
  detaches itself from the colony as a new medusa,
  and the reproductive cycle repeats.

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Homework due 3/7/08

• Pick one of the coral reefs listed on the next
  slide or one of the State Parks from the list to
  study.
• List the 3 things you found most interesting and
  tell me why.
• List 3 ways the reef is being damaged.
• List 3 ways the reef is being protected.
• Describe the coral reef you have choosen. (In
  your own words) Minimum 2-3 paragraphs. (Pretend
  you are planning a trip there and want to
  convince me to go with you. What would you say
  to convince me to go and what would I need to
  know about the reef before I got there.)

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Homework for 3/07/08
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State Parks with Coral Reefs

• 1. Biscayne, Florida
• 2. Dry Torugas, Florida
• 3. Buck island Reef, St. Croix
• 4. Salt River Bay, St. Croix
• 5. Virgin islands, St. John
• 6. U.S.V.I. Coral Reef national Monument
• 7. War in the Pacific, Guam
• 8. National park of American Somoa
• 9. Kalaupapa National Historic Park, Hawaii
• 10. Kaloko-Honokohau Park, Hawaii