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Cnidarians
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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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4. 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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5. Cnidarian Characteristics
Either tubular or bell shaped
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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6. 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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7. Extracellular Digestion
Food digested outside of cells
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Cnidocyte
Coiled nematocyst
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9. 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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12. Jellylike mesoglea between two cell layers supports cnidarian
mesoglea-filled bell
tentacles
Jellylike mesoglea between two cell layers supports cnidarian
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13. 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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Cnidarian Diversity
Scyphozoans:
Jellyfish
Anthozoans:
Sea anemones
Corals
Hydrozoans:
Hydra
Cubozoa
Box Jellies
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Cnidarian Diversity
Coral polyps
Jellyfish
Sea Anemone
Coral polyps
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17. More Cnidarians
Brain Coral
Red jellyfish
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Anthozoans
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19. Anthozoan Characteristics
Sea Anemones
Brightly colored & Resemble flowers
Solitary polyps
Feed on invertebrates & fish
Corals
Most are colonial
Build limestone case
Live as polyps in their case
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Sea Anemones & Coral
Exist only as Polyps
Clownfish live in anemone tentacles
Corals build a limestone case which build up & form reefs
ANEMONE
CORAL
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22. Distribution of Coral Reefs
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Hydrozoans
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Hydrozoans
Hydra
Exist only as polyps
Reproduce by budding
Freshwater only
Form resistant zygotes when environment is bad
Move by somersaulting with tentacles
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Hydra
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Hydra Feeding
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27. Food in Gastrovascular Cavity copyright cmassengale

28. Portuguese man-of-war copyright cmassengale
Colonial Hydrozoan (not a single organism
Tentacles sting prey such as fish & humans
Polyps in colony feed
Has gas-filled air float
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30. Portuguese Man of War - cnidarian that floats in the water and has long tentacles

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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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33. 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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Cubozoans
Box JellyFish
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Scyphozoans
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36. Scyphozoan Characteristics
Jellyfish
Medusa is dominant body form
Go through small polyp stage during life cycle
Stinging tentacles
May live close to shore or the open ocean

37. Parts of a Jellyfish 37 37

38. Some Jellyfish Show Luminescence38 38

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40. Jellyfish Life Cycle

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42. Multimedia
Sponge Images and Videos -
Cnidarian Images and Videos -
General Invertebrate Movies at National Geographic 
--- really good video on the portuguese man of war (under invertebrates)
Hydra Video at