Phylum Cnidaria
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Transcript of Phylum Cnidaria
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Jellyfish, hydra, sea anemones, & coral
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Cnidarian questions1. What do we already know about
Cnidarians (from the phlyo. Tree)1. Two tissue layers (germ layers)(ecto and
endoderm)1. “diploblastic”
2. Radial Symmetry2. Look at the life cycle of a jellyfish…
A. What are the two body types of Cnidarians?B. Which is mobile? Sessile?
A. Medusa is mobileB. Polyp is sessile
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AppearancePolyp: cylindrical, vase shaped animals that are usually attached to a rock or sea floor
Ex. Hydras, sea anemones, corals
Medusa: bell-shaped body; umbrella
Ex. Jellyfish
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Appearance (cont.)
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SymmetryRadial symmetry
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Skeletal/Muscle SystemNO MESODERM, so…no real muscles!
most have primitive muscle cells coral have external skeleton of calcium
carbonate
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Capturing Prey LET’S EAT!!!cnidarians are
carnivores (eat meat) use tentacles
arranged in a ring around their mouth to capture prey
when a “trigger” is stimulated on a stinging cell called the cnidocyte, a harpoon or nematocyst shoots out & injects poison into the prey
Cnidocyte (stinging cell)
Nematocyst (harpoon)
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Capturing Prey: Cnidocyte and Nematocyst at work
Cnidocyte (stinging cell)
Nematocyst (harpoon)
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DigestionSac w/ a digestive cavity (gastrovascular
cavity) w/ a single opening that acts as a mouth/anus
Jellyfish Hydra
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Digestion (cont.)food is pushed into the gastrovascular cavity
where digestion begins (extracellular digestion)
undigested remains leave through the mouth/anus
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Nervous SystemNo brain or even ganglia, no
cephalization, etcNerve Net- have simple sensory receptors
that detect & respond to stimuli
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CirculationNONE!!
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RespirationDiffusion- oxygen from water moves into
cells (high to low)
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Reproduction Asexual – budding- formation of
outgrowths that pinch off from parent to live independently
Sexual- forms a zygote and free swimming form that settles on ocean floor (usually a polyp)
*MOST ALTERNATE B/W POLP & MESDUSA LIFE FORM
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Reproduction (cont.)
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Reproduction (cont.)
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ExcretionDiffusion to release waste
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Class Hydrozoa • Ex- Hydra•both asexual polyps and sexual medusa stages•Spends most of its life in the polyp stage
Reproduction: •Sexual: eggs and sperm are shed into the water and form fertilized eggs; planula is by passed with eggs hatching into young hydras •Asexual reproduction via budding
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Class Hydrozoa cont.
Other Hydrozoans
Portuguese man-of-war: Single gas-filled float with tentacles Tentacles house the polyps and modified medusae of the colony
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Class Scyphozoa
Jellyfish• The medusae are large and contain massive amounts of mesoglea•Sexual and Asexual reproduction
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Class Anthozoa
•include sea anemones and coral
•Exclusively marine; there is no medusa stage
• Most anthozoans are colonial (e.g. corals) and secrete external skeletons composed of calcium carbonate.
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