(Péron and Lesueur, 1810)
Description
Umbrella usually higher than wide with pointed or dome-shaped apex; exumbrella smooth, with a circular, coronal furrow situated midway between umbrella margin and apex; jelly thick, rigid. Form of the umbrella is changing with growth [P.periphylla-umbrella ]. Sixteen pedalial thickenings, four of which are interradial marginal sense organs, with four perradial and eight adradial solid marginal tentacles in groups of three situated between; rhopalar pedalia slightly narrower than tentacular pedalia.
Stomach large, occupying whole of upper part of central dome; attached interradially to subumbrellar summit over four elongated triangular gastric septa; eight phacelli, one along each side of triangular gastric septa, each with 140+ simple gastric filaments, in total more than 1,120. Manubrium with four broad perradial thickenings, not extending beyond umbrella margin.
The eight gonads forming four long U-shaped groups looping across the lower 2/3 of the bell, straddling interradial septa; each gonad with horizontal folds directed outwards.
Size
Umbrella up to 35 cm in height, 25 cm wide.
Colour
Stomach and manubrium deep reddish brown to brownP.periphylla-habitus; exumbrella and subsurface-tissues colourless.
Ecology
Medusae can be found throughout the year.
Depth range
Seems to have a diel migration range of at least 500 m; maximum recorded depth is 2,700 m (Russell, 1970a), but also found at the surface in high latitudes and the Mediterranean.
Distribution in the North Sea
Northern North Sea, off Bergen (Norway), also in Skagerrak.
World distribution
Cosmopolitan with a wide distribution in the Atlantic, except the Arctic.
Remark
Polypoid stage absent.
[After Russell, 1970a; Russell, 1976]