L. Agassiz, 1862
Description
Umbrella bell-shaped, higher than wide with rounded apex; umbrella margin oblique; apical process absent; jelly thick, especially on tentacular side. Exumbrella with five meridian nematocyst tracks, two tracks issuing from tentacular bulb, one track of each reduced non-tentacular bulb. Tentacular bulb with one or more moniliform tentacles [H.prolifer-medusa ] and with medusa buds [H.prolifer-asexual-habitus ].
Four radial canals and ring canal fairly broad, radial canal on tentacular side longest. Manubrium large, cylindrical, mounted on short peduncle; mouth simple, tube-like, surrounded by narrow ring of nematocyst batteries.
Gonads completely surrounding manubrium; eggs amoeboid, developing into actinulae in bell cavity.
Size
Umbrella 3 mm wide, 4 mm high.
Colour
[H.prolifer-male-habitus ] Marginal bulbs, mouth and apical end of manubrium bright red or reddish brown; manubrium pale yellow; ectoderm of marginal tentacle, surface of subumbrella and exumbrellar nematocyst tracks pink.
Ecology and depth range
Neritic. In British waters the medusae can be found in spring and early summer, peak abundance in April and May.
Distribution in the North Sea
Throughout southern and northern North Sea.
World distribution
North Atlantic Ocean including Arctic waters and Mediterranean Sea; W South Atlantic and Indo-Pacific Oceans.
[After Russell, 1939; Russell, 1953a; Bouillon, 1999]