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Cnidarians
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Phylum Cnidaria
About 9000 species
Most are marine (jellyfish, coral, sea anemones, Portuguese man-of war)
Hydras are found in freshwater
All have arm-like tentacles
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5. Cnidarian Characteristics
Radial symmetry
Hollow gut -Gastrovascular cavity has single opening (serves as both mouth and anus)
Two tissue layers (diploblastic)
Outer epidermis and inner gastrodermis
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6. Two Main Body Plans of Cnidarians
UPRIGHT TENTACLES
TENTACLES HANG DOWN
Polyp
epidermis
mouth
mesoglea
gastrodermis
Medusa
Mesoglea THICK
Mesoglea THIN
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7. Medusa –(snakes for hair) In Greek mythology she was a female monster, gazing upon her could turn someone to stone. She was beheaded by Perseus who used her head as a weapon.

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9. Cnidarian Characteristics
Tentacles surround mouth
Only animal with cnidocytes (stinging cells) found in the tentacles
Nematocyst – coiled, harpoon-like stinger inside cnidocyte that shoots out
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10. Cnidarian Characteristics
Cnidocytes contain poison to paralyze prey
Tentacles bring food into mouth
Inner gastrodermis secretes digestive juices into gastrovascular cavity which digests food and circulates nutrients
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11. Extracellular Digestion
Food digested outside of cells
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Cnidocyte
Coiled nematocyst
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13. Barbed, threaded stinger copyright cmassengale
Nematocyst
Barbed, threaded stinger
capsule’s lid
trigger
nematocyst
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Cnidarian Systems
Have a simple nerve net & sensory receptors
Muscles help in directional movement & capturing prey
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16. Jellylike mesoglea between two cell layers supports cnidarian
mesoglea-filled bell
tentacles
Jellylike mesoglea between two cell layers supports cnidarian
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Cnidarian Diversity
Coral polyps
Jellyfish
Sea Anemone
Coral polyps
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Cnidarian Diversity
Scyphozoans:
Jellyfish
Anthozoans:
Sea anemones
Corals
Hydrozoans:
Hydra
Portuguese Man-of-War
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Anthozoans
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21. Anthozoan Characteristics
Ex. Sea Anemones
Brightly colored and resemble flowers
Only live as solitary polyp
Feed on invertebrates and fish
And photosynthetic symbionts.
Clownfish live in anemone tentacles (type of symbiosis?)
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22. Anthozoan “flower animal”
Ex. Corals
Individual polyps that live in colonies.
Motile larva
Secretes a limestone case which build up & form reefs
Live as polyps in their case
CORAL
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24. Distribution of Coral Reefs
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Hydrozoans
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Hydrozoans
Ex. Hydra
Exist only as polyps
Reproduce by budding
Found only in freshwater
Form resistant zygotes when environment is bad
Move by somersaulting with tentacle
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Hydra
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Hydra Feeding
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29. Food in Gastrovascular Cavity copyright cmassengale

30. Portuguese man-of-war copyright cmassengale
Colonial Hydrozoan (a group of polyps living together)
Tentacles sting prey such as fish & humans
Each polyp has a job.
1.Produces tentacles to capture food.
2. Make gas-filled air float
3. Make sperm/eggs
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Scyphozoans
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37. Scyphozoan “cup animals”
Ex. Jellyfish
Medusa is dominant body form
Go through small polyp stage during life cycle.
Reproduce using both asexual and sexual cycles
Stinging tentacles
4m-30meters long
May live close to shore or the open ocean

38. Parts of a Jellyfish 38 38

39. Some Jellyfish Show Bioluminescence39 39

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Hydrozoan Life Cycle
Most hydrozoans alternate polyp and medusa forms, as in the life cycle of Obelia
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44. Obelia Life Cycle (Hydrozoan) Larva called a planula
female medusa
male medusa
reproductive
polyp
sperm
ovum
feeding polyp
zygote
polyp forming
planula
Fig a, p.411
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45. Jellyfish Life Cycle