Phylum Cnidaria

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Phylum Cnidaria

• Jellyfish, hydra, sea anemones,
• coral

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Cnidarian questions

• What do we already know about Cnidarians (from
  the phlyo. Tree)
• Two tissue layers (germ layers)(ecto and
  endoderm)
• diploblastic
• Radial Symmetry
• 2. Look at the life cycle of a jellyfish
• A. What are the two body types of Cnidarians?
• Which is mobile? Sessile?
• Medusa is mobile
• Polyp is sessile

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Appearance

• Polyp 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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Symmetry

• Radial symmetry

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Skeletal/Muscle System

• NO MESODERM, sono real muscles!
• most have primitive muscle cells
• coral have external skeleton of calcium carbonate

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Capturing Prey LETS EAT!!!
Nematocyst (harpoon)

• 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)
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Capturing Prey Cnidocyte and Nematocyst at work
Nematocyst (harpoon)
Cnidocyte (stinging cell)
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Digestion

• Sac 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 System

• No brain or even ganglia, no cephalization, etc
• Nerve Net- have simple sensory receptors that
  detect respond to stimuli

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Circulation

• NONE!!

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Respiration

• Diffusion- 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 planula
  that settles on ocean floor
• MOST ALTERNATE B/W POLP MESDUSA LIFE FORM

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Reproduction (cont.)
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Reproduction (cont.)
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Excretion

• Diffusion to release waste

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Cnidarian Taxonomy
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• Class Hydrozoa
• Ex- Hydra
• both asexual polyps and sexual medusa stages

• 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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