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(Linnaeus, 1766)

Description
Umbrella saucer-shaped, with thick jelly and smooth exumbrella. Ring canal lacking. Marginal lappets 32-48, semi-circular in outline, clefts between tentacular lappets uniform in depth.
Four perradial and four interradial rhopalia; tentacles 24 in adult, three of uniform size per octant, all arising from edge of disc in cleft between lappets.
Stomach pouches 16; in marginal zone, typically having the eight rhopalar stomach pouches much narrower than the eight inter-rhopalar pouches. Rhopalar and tentacular pouches simple and unbranched.
Length of oral arms up to ca. five times bell diameter, narrow, V-shaped in section, edges frilled, extreme terminal region (may be lost) spirally coiled. Radial septa typically narrow, becoming wider centripetally only gradually, inner end roughly truncate.
Thickened subumbrellar basal portions of manubrium fused to form four gonadial pouches with circular or oval orifices [C.hysoscella-subumbrella ].

Size
Umbrella up to 30 cm in diameter.

Colour
Colouration greatly varied, but the lappets are typically brown [C.hysoscella-habitus ]; the rest of bell is colourless, or variously coloured, or with varied pattern of radiating lines or patches [C.hysoscella-pigment patterns ]. Type 1 (fig. C) without a pattern; Type 2 (fig. A) with a dark pattern on a light background; and Type 3 (fig. B) with a light pattern on a dark background [C.hysoscella-patterns ]. Some lines meeting near-centrally to form isosceles triangles, some specimens having the ‘triangles’ filled in. Ground colour varied from colourless through white to yellow, orange and brown, radial lines varied from red through orange to chocolate. Mouth arms white, yellowish to orange, perhaps also brown.

Ephyra
Ephyra C.hysoscella-ephyra with nematocyst clusters. Developmental stages (figs. A-F, increasing in size) C.hysoscella-development.

Ecology
In British waters young medusae first appear in May, peak abundance of larger specimens from mid-June to September. Off the Dutch coast, peak abundance from mid-August to mid-October.

Depth range
More abundant in the water column at times of ebb and flow with strong currents, than during periods of slack water. Usually swimming at several feet below the surface.

Distribution in the North Sea
Throughout the whole North Sea, also reported from the Kattegat.

World distribution
North and South Atlantic Oceans, as far south as Tierra del Fuego; the Mediterranean Sea and Adriatic.

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

Chrysaora hysoscella