Duncecap or helmet jelly Periphylla periphylla

Periphylla periphylla is found in Antarctica and the Antarctic Peninsula, South Shetland Islands, South Sandwich Islands, South Georgia Island, the Southern Ocean, and worldwide (except in the Arctic) in depths from about 200 to 1000 meters but it can be at the surface in high latitudes especially at night [1]. Diving under the ice in Antarctica is equivalent to this latter condition. P. periphylla is the most widely distributed and abundant scyphomedusa in deep water [1]. P. periphylla has a thickened and conical or hemispherical central dome and it can be up to 35 centimeters in diameter [1]. P. periphylla has a large dark red or dark brown stomach, occupying the upper portion of the dome [1,5]. P. periphylla has twelve tentacles and captures small zooplankton with its rigid upward-pointing tentacles; its tentacles are then bent down and inward in order to bring prey to its mouth [1,2]. The coronal groove around the lower portion of its bell or umbrella acts as a hinge to provide flexibility for swimming and to contain prey during feeding [2].



Periphylla periphylla which get close enough to the bottom in shallow water are prey to be captured by tentacles of an anemone (Isotealia antarctica shown here) [3]. The struggle can continue for quite awhile. The medusa pulses its bell as it tries to swim away while the anemone slowly pulls the medusa into its mouth.



Anemone-captured P. periphylla can be nibbled by sea spiders passing by the anemone [4].

1: Pelagic Scyphomedusae (Scyphozoa: Coronatae and Semaeostomeae) of the Southern Ocean. RJ Larson. Washington, DC: American Geophysical Union, 1986; 2: Marine Behavior and Physiology 6(2):123-129, 1979; 3: Antarctic Ecology, Volume 1. MW Holdgate, ed. NY: Academic Press, 1970. pp.244-258; 4: Peter Brueggeman, personal communication (observed sea spider eating anemone-captured medusa), 1999; 5: Scientia Marina 56(Supplement 1):1-64,1992

Text ©Peter Brueggeman. Photographs ©Norbert Wu. Photographs may not be used in any form without the express written permission of Norbert Wu. Norbert Wu no longer grants permission for uncompensated use of his photos under any circumstances whatsoever; want more info?