(Mayer, 1900)
Description
Umbrella bell-shaped, with considerable solid, elongated-conical or hemispherical apical projection [Amphinema rugosum ]. Jelly moderately thick, velum moderately broad. The four undivided radial canals and ring canal broad with smooth or only slightly jagged outlines, interradial centripetal canals absent. Gastric peduncle absent, manubrium with broad base, sessile.
Manubrium cross-like in section, flask-shaped, almost as long as bell cavity. Mouth with four prominent, recurved crenulated lips.
Eight adradial gonads on manubrium wall only, gonads with three or four folds sloping obliquely downwards towards interradii [A.rugosum-male ]. Umbrella margin with two opposite, hollow, perradial tentacles with large hollow, elongated, basal swellings, and 16-24 small tentaculae. Ocelli absent.
Young: A.rugosum-young-habitus .
Size
Umbrella up to 6 mm high, 1.5 times higher than wide.
Colour
[A.rugosum-habitus ] Marginal tentacle bulbs and manubrium rich brownish yellow to orange, with central masses of deep purple-brown pigment; cores of the two marginal tentacles yellow ochre; marginal tentaculae colourless.
Ecology and depth range
In south-western British waters medusae appear in the plankton in spring and summer months.
Distribution in the North Sea
Southern North Sea, Skagerrak (also English Channel).
World distribution
North Atlantic and NW Pacific Oceans.
[After Russel, 1953a; Russell, 1955; Kramp, 1959]