Cnidarians

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Cnidarians
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Characteristics

• Greek (knide nettle) to sting
• Radial symmetry
• Motile and sessile
• Two tissues layers
• Gastrovascular cavity
• Nerve net

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Characteristics cont

• Two forms

POLYP stationary, vase-shaped
MEDUSA mobile, cup-shaped
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Body Plan

• Two tissue layers
• Epidermis
• Gastrodermis
• Jelly-like mesoglea in between the two tissues

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Body Plan cont.

• Cnidocytesspecialized stinging cells
• Nematocysts the barbs on the stinging cells

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Feeding

• GVC beginnings of a digestive system
• Extracellular
• Can digest food bigger than their cells
• Tentacles with cnidocytes
• Sting
• Pull prey into mouth
• Two way system
• In and out mouth

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Reproduction

• Asexual
• Budding and regeneration
• Sexual
• Ovaries produce eggs
• Testes produce sperm

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Cnidarian Classes

• Hydrozoa
• Hydra, Obelia, Portuguese Man of War
• Polyp is dominant stage

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Portuguese Man of War (Physalia)
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Scyphozoa

• True JellyfishAurelia
• Medusa is the dominant stage

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Anthozoa

• Corals, sea fans anemones
• Only polyps
• Corals are among most productive ecosystems on
  earth
• Support commercial fisheries
• Commercial pets/aquariums

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Cubozoa

• Includes one of the deadliest animals on earth
  (may be the deadliest)
• Sea Wasps (box jelly)
• Death occurs in 3-20 minutes!!

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