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(Forskål, 1775)

Description
Umbrella hemispherical to somewhat flattened; jelly thick; exumbrella with a variety of medium sized nematocyst warts (longer in some specimens or populations) [P.noctiluca-b/w photo]. Ring canal lacking.
Eight adradial, hollow, marginal tentacles alternating with eight marginal rhopalia; marginal tentacles 2-3 times umbrella radius in length, with 30 or more longitudinal muscle furrows embedded in the thick mesogloea.
Sixteen marginal lappets, rectangular in shape with rounded corners. Four interradial gonads much-folded and elongate, the central folds bulging downwards between thickened bases of manubrium [P.noctiluca-subumbrella ].
Gastrovascular sinus divided by radial septa into separate rhopalar and tentacular pouches; the 16 pouches are all alike, each terminating in pair of unbranched canals or subpouches which enter marginal lappets.
Oral arms at about five times bell height, simply frilled, also with numerous warts.

Size
Umbrella up to 12 cm in diameter.

Colour
Somewhat varied; ground colour of bell transparent to milky, warts red/magenta to brown and giving colour to bell; mouth arms and marginal tentacles colourless or red/magenta to brown [P.noctiluca-habitus ].

Ephyra
The presence of nematocyst warts on the exumbrellar surface is a useful character for identification [P.noctiluca-ephyra ]. Juvenile with the four primary marginal tentacles well developed and the secondary marginal tentacles not yet, though they have appeared [P.noctiluca-juvenile ]. Nematocyst warts present.

Ecology
Usually found off shores in late summer and winter, generally occurs in large swarms in the open sea.

Depth range
In the open ocean the bulk of specimens is found in the upper 200 m of the water column, but specimens have been caught considerably deeper.

Distribution in the North Sea
Throughout the North Sea from S Norway to the English Channel, including Skagerrak; absent from the Baltic Sea.

World distribution
North Atlantic Ocean, Norwegian Sea.

Remark
Polypoid stage absent.

[After Russell, 1970a; Russell, 1978a; Bouillon, 1999]

Pelagia noctiluca