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Phylum Cnidaria
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Phylum Cnidaria – “stinging cell”
A.k.a Coelenterata (hollow cavity) Radiata (radial symmetry)
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Jelly Fishes
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Sea Anemones
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Corals
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One step above sponges…
Differ from sponges - have rudimentary organs Incomplete digestive & excretory systems No blood or circulatory system
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Classification 3 Classes Hydrozoa = Hydra Scyphozoa = Jellyfish
Anthozoa = Sea anemones & coral
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Morphology Body wall - 3 layers Epidermis (outside)
Mesoglea (inner transluscent jelly-like material) Gastrodermis (inside lining)
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Skeletal Structure Corals secrete calcium carbonate to build exoskeleton Most sea anemones and hydra use water pressure from inside body cavity (hydrostatic pressure) to maintain body form
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Body Features Mouth usually surrounded by tentacles (radial symmetry)
Tentacles covered in cnidocytes = specialized stinging cells Nematocysts = Shoots like a harpoon from cnidocyte. Contains deadly toxin. Gastrovascular cavity – Hollow digestive cavity Mouth serves as entrance/exit point
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Nervous System No brain Nerve net Capable of responding to stimuli
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Habitat Aquatic, mostly marine
Hydra – Freshwater, independent, free swimming Jellyfish – Marine, independent, free swimming Coral & Anemone – Marine, sessile, colonial
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Body Forms Polyp – present in all 3 classes Hollow tube with tentacles
Can be free swimming (hydrozoa, scyphozoa) or sessile (anthozoa)
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Body Forms Medusa – only present in hydrozoa and scyphozoa
Free swimming Umbrella shaped with tentacles Mesoglea constitutes bulk
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Reproduction Hydrozoa & Scyphozoa – Anthozoa –
Asexual reproduction in polyp form by budding Sexual reproduction in medusa form Anthozoa – No medusa form, but can reproduce asexually (budding) or sexually
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Close-up of Hydrozaon polyp
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Hydrozoan medusa
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