The helmet jellyfish (Periphylla periphylla) is a bioluminescent, red-colored jellyfish that lives in the disphotic and aphotic zones. It is the only species in the monotypic genus Periphylla.
Helmet jellyfish reach a body size of up to 30 cm. They consist 90% of water, the rest being tissue and mesoglea, which give the animals their form. They use bioluminescence, the red flashes serving as a signal amongst themselves. Between their marginal lobes sit small sense bulbs, by which the helmet jelly can distinguish between light and dark; they have been observed to avoid light.
In many fjords of Norway, the helmet jelly has proliferated since the 1970s. It has become a competitor of fish for food and is thereby also a threat to the fishing industry. These jellyfish should have been deprived of their own food basis by displacement of almost all other sea creatures, yet the swarms of crown jellies still live.
The cause is being studied at this time by marine biologist Ulf Båmstedt. Also not far from Bergen, in the Lurefjord, helmet jellies have proliferated. The objective is to find a possible explanation for the new mass development.
The ecology and population dynamics will be investigated by Norwegian and American work groups. The ontogeny, in particular, the development of pigmentation, luminescence, food absorption and sense capacity, will be researched in a Hamburg workgroup.