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Animal Notes 3 ( Cnidarian Notes)

Biology 11

Thank to Ms. L. Jamieson

Name: __________________________ Date: ___________ Block: ____



Phylum Cnidaria:

(Greek: cnidos = “stinging needle”)

Pages 306-309


  1. Background


  • 4 Major Classes:
    1. _______________:True coral, Sea Anemones, Sea Pens – ~6000 spp
    2. _______________: Box Jellyfish, Sea Wasps – ~20 spp
    3. _______________: Hydroids, Freshwater Hydra, Fire Coral – ~3000 spp
    4. _______________: True Jellyfish – ~200 spp


DID YOU KNOW!!!: The “Box Jellyfish” has the most potent venom of any animal on the

planet. A sting from these Australian jellyfish is usually fatal


  • Most Cnidarians are _______________, but some live in _______________


  1. Body Plan/Structure:
  • The Cnidarian have a _______________ symmetrical body plan
  • They are the first Phylum that we will study with a true _______________ (gut)
  • There is only one opening into the _______________ which serves the function of _______________ and _______________
  • Like the Sponges they only have two germ layers:
    1. _______________ : Outside
    2. _______________ : Inside
    3. _______________ (Not really a germ layer): A jelly-like material that lies between the _______________ and the _______________
  • They do not have organs but do have _______________ and _______________ (but no brain)
  • They do not have a _______________


DID YOU KNOW!!!: Up to 95% of a Cnidarian’s body may be water!!!




  • All Cnidarians have _______________ around the _______________ which they use to catch food
    • The tentacles have special cells called _______________. Inside these _______________ are little harpoons called _______________ which fire to capture food


  • Cnidarians demonstrate _______________ in their lifecycle:
    • They have a _______________ of their lifecycle which is _______________ and _______________ (eg. Anemone)
    • They also have a _______________ of their lifecycle which is _______________and _______________ (eg. Jellyfish)


III. Feeding:


  1. Capturing Prey:
  • Cnidarians use _______________ to capture food
  • Thousands of special cells on the tentacles, called _______________, contain sacs called _______________
  • The _______________ contain a coiled, hollow, threadlike tube which is often filled with _______________.
  • When a tentacle brushes up against something it triggers the _______________ to fire the harpoon-like threads in order to _______________, _______________ and sometimes _______________ the prey
  • The _______________ form is _______________ and must wait for prey to come close enough to capture it while the _______________ form is _______________ and accidentally swims close enough to prey to capture it (they don’t have a brain so they don’t think about what they’re doing).


  1. Digestion:
  • Captured prey is brought to the _______________ by the tentacles
  • The food is taken into the _______________ where it is digested
  • The nutrients from the digested prey are absorbed into the _______________ where they _______________ throughout the Cnidarian


  1. Respiration:
  • _______________ is absorbed directly into the cells of Cnidarians from the surrounding water by _______________
  • _______________ is released directly from the cells of Cnidarians into the surrounding water by _______________diffusion




  1. Excretion:
  • Undigested food is released back into the water through the _______________
  • Metabolic wastes are released directly from the cells of Cnidarians into the surrounding water


  1. Response:
  • Cnidarians do not have a brain, but they have a _______________ that encircles the body
  • The _______________ is a very simple type of _______________ that controls simple ____________ and is used for movement and to control the ___________


  • Cnidarians can also sense and respond to their surroundings.       These include:
    1. Sense and respond to _______________
    2. Sense and respond to _______________
    3. Sense and respond to _______________
    4. Sense and respond to _______________
    5. Sense and respond to _______________


VII. Reproduction:

  • Alternation of Generations:
    • Aexual Reproduction:
      • The sessile polyp stage undergoes _______________ reproduction by _______________
      • _______________ gives rise to the _______________ stage of the life cycle
    • Sexual Reproduction:
      • The _______________ stage can be either _______________ or _______________
      • The _______________ develop and cluster in the _______________ to form “_______________” (not true organs)
      • The gametes are released into the water
      • When a _______________ cell meets an _______________ cell in the water it fertilizes it
      • The fertilized egg (_______________) develops into the _______________ larva stage called a _______________
      • The _______________ eventually attaches to an object to form a new p_______________ stage


DID YOU KNOW!!!: Some Cnidarians like Sea Anemones and Coral (Anthozoans) do not have a medusa stage in their lifecycle. Instead they are hermaphroditic and release both eggs and sperm directly into the water.


VIII. Movement:

  • The _______________ form of Cnidarians are _______________
  • The _______________ form of Cnidarians are _______________


  1. Colonial Specialization
  • Some Cnidarians can form colonies
  • Most of the colonies are formed during the _______________ stage of the lifecycle but some Cnidarians form colonies during the _______________ stage of the lifecycle
  • Colonies allow for _______________ of parts
  • These colonies are formed from many polyps each with a specific function
  • One example of a colonial Cnidarian is The Portugese Man ‘O War, which contains polyps sepecialized for _______________, _______________, _______________, and_______________

DID YOU KNOW!!!: Corals are gigantic colonies of Cnidarian polyps. These polyps secrete

calcium carbonate for protection which gives Corals all of their cool shapes!!!.


DID YOU KNOW!!!: As Corals die new ones grow over the dead calcium carbonate skeletons. Many generations of settlement, growth and death result in huge reefs like the Great Barrier Reef, hundreds of feet thick and millions of years old!!!.


  1. Ecological Roles of Cnidarians:
  • _______________ and _______________ form symbiotic relationships with thousands of other organisms
  • Some anemone form symbiotic relationships with _______________
  • Both anemone and coral provide _______________, _______________, and _______________ for thousands of organisms
  • Coral reefs also help humans in many ways
    • The protect the coastal land from damaging waves
    • They also create amazing waves that many people enjoy surfing
    • Many people around the world rely for food on the abundant coral reef fish


DID YOU KNOW!!!: The Bonsai Pipeline off the North Shore of Hawaii is created by a reef that lays only a few feet beneath the surface of the ocean!!!.


  • Coral Bleaching:
    • The coral reefs around the world are quickly being destroyed.
    • Pollution created by us humans is killing the polyps of the coral leaving behind the white calcium carbonate reef. This is called coral bleaching.
    • The calcium carbonate reefs are much more fragile and are destroyed by waves which destroys many of the ecosystems found in the coral reefs
posted by Marc Bernard Carmichael in Biology Eleven,Biology Eleven Notes,Cnidaria and have No Comments

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