The phylum Cnidaria include sea anemones, sea jellies and corals.

The Greek word "cnidos" means "stinging nettle." When agitated they eject a barbed thread often with a venom. The sea anemones in our local tide pools are harmless.

Characteristics include:

  • Radial Symmetry
  • Cnidocytes (stinging cells)
  • Almost all marine
  • Presence of tissues - allows for more complex functions
  • One single opening - mouth and anus opening into a blind pouch (gastrovascular cavity)
  • Two body forms Medusa (planktonic) and Polyp (sessile)
  • Life cycles may alternate between the two body forms

More information on cnidaria can be found be going to the Cnidarian Research Center. Some great photos of cnidaria can be found at UCSD underwater field guide.

Zonation | Intertidal Pools | Collection Etiquette

Kelp & Algae | Fungi | Porifera | Cnidaria

Mollusca | Echinodermata | Osteichthyes

Tides | References