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Moon jelly (Aurelia aurita) with rhopalia visible in indentations of rim

Rhopalia (singular: rhopalium) are small sensory structures of Scyphozoa (typical jellyfish) and Cubozoa (box jellies). In Aurelia they lie in marginal indententions around the bell and are flanked by rhopalial lappets. Specialized structures to sense light (ocelli) and perceive gravity (statoliths) are usually present. They also control the pace of swimming-muscle contraction.

Cubozoan ocelli are the most complex of Cnidarians, and resemble the image-forming eyes of squids, octopuses and vertebrates.

swing of the rhopalia of Tripedalia cystophora

See also[edit]


  • Meglitsch, Paul A. (1991). Invertebrate Zoology, Oxford University Press, 86. ISBN 0-19-504900-4.
  • Ruppert, Edward E.; and Fox, Richard S. (1988). Seashore Animals of the Southeast, University of South Carolina Press, 29. ISBN 0-87249-535-3.

External links[edit]