Helmet Jelly fish (Periphylla). This is a common deep sea species. At locations dominated by strong tidal currents, forcing water from 200 meters or more up towards the surface, they can be encountered at any depth. At some locations this phenomenon is highly seasonal. An example is Lurefjorden (Hordaland) where water from 200 meters depth is forced into the fjord through a shallow (20 meters) and narrow (200 meters) sill entrance. The maximum recorded depth is 2700 meters.