The common jellyfish, Aurelia, belongs to a very primitive group of organisms, the coelenterates. These are peculiar in that they have only one opening to their alimentary canal which is situated in the middle of the under surface of the umbrella, and serves both to take in food and to discharge waste. Around the mouth are a number of stinging cells which paralyse the prey before it is eaten. Aurelia, however, feeds mostly on tiny plankton organisms and is harmless to man, though some other members of the coelenterate family can produce a very painful sting.
by Richard Morrison Cassie, M.SC.(N.Z.), D.SC.(AUCK.), Senior Lecturer in Zoology, University of Auckland.