1 Cnidarians & Ctenophorans 1 copyright cmassengale
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Phylum CnidariaPhylum 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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Cnidarian Cnidarian CharacteristicsCharacteristics
•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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Cnidarian Cnidarian CharacteristicsCharacteristics
•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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Cnidarian Cnidarian CharacteristicsCharacteristics
•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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Extracellular DigestionExtracellular Digestion
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Food digeste
d outside of cells
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NematocystNematocyst
Barbed, threade
d stinger
capsule’s lid
trigger
nematocyst 9copyright cmassengale
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Cnidarian SystemsCnidarian Systems
•Have a simple nerve net & sensory receptors•Muscles help in directional movement & capturing prey
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mesoglea-filled bell
tentacles
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Jellylike mesoglea
between two cell layers supports cnidarian
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Two Main Body Plans of Two Main Body Plans of CnidariansCnidarians
epidermis
mesoglea
gastrodermis
Medusa
Polyp
UPRIGHT TENTACLESTENTACLES HANG DOWN
mouth
Mesoglea THICK Mesoglea THINcopyright cmassengale
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Cnidarian DiversityCnidarian Diversity
• Scyphozoans:
Jellyfish
• Anthozoans:
Sea anemones
Corals
• Hydrozoans:
Hydra
• Cubozoa
Box Jellies15copyright cmassengale
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Cnidarian DiversityCnidarian Diversity
16Sea Anemone Coral polyps
JellyfishCoral polyps
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Scyphozoan Scyphozoan CharacteristicsCharacteristics
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
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Anthozoan Characteristics
Sea AnemonesBrightly colored &
Resemble flowers
Solitary polyps
Feed on invertebrates & fish
CoralsMost are colonial
Build limestone case
Live as polyps in their case
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Sea Sea Anemones Anemones
& Coral& Coral•Exist only
as Polyps
•Clownfish live in anemone tentacles
•Corals build a limestone case which build up & form reefs
ANEMONE
CORALcopyright cmassengale
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HydrozoansHydrozoansHydra
•Exist as polyps in their dominant form.
•Reproduce by budding
•Freshwater only
•Form resistant zygotes when environment is bad
•Move by somersaulting with tentacles
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•Colonial Hydrozoan (not a single organism
•Tentacles sting prey such as fish & humans
•Polyps in colony feed
•Has gas-filled air float
Portuguese Portuguese man-of-warman-of-war
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Hydrozoan Life CycleHydrozoan Life Cycle
Most hydrozoans alternate polyp and medusa forms, as in the life cycle of Obelia
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ObeliaObelia Life Cycle (Hydrozoan) Life Cycle (Hydrozoan)Larva called a Larva called a planulaplanula
reproductivepolyp
female medusa male medusa
sperm
zygote
ovum
planulaplanulapolyp formin
g
feeding
polyp
Fig. 25-15a, p.411copyright cmassengale
Chironex fleckeri
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Australian shores
100 human deaths in the last 100 years
Venom can kill in 3 minutes
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Ctenophoran Ctenophoran CharacteristicsCharacteristics
•Called comb jellies
•All marine
•Approximately 100 species
•May be spherical, ovoid, or elongate in appearance
•Bioluminescentcopyright cmassengale
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Ctenophoran Ctenophoran CharacteristicsCharacteristics
•Radial symmetry
•Have eight plates of fused cilia that resemble combs
•Move by beating cilia
•Most of the body is jelly-like mesoglea
•Body & tentacles covered with sticky mucus to catch prey
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