Brandt, 1838
Disc flat (when resting), typically to 60 cm, some to ca. 1.5 m diameter; jelly moderately thin, flexible. Marginal lappets 16, broad, curved, outer margin shallowly divided into sub-lappets (each supplied by a radial canal) in some individuals. Rhopalia 16, in deep clefts. Rhopalial lappets typically in pairs forming Y, arms of Y distal and free, rhopalium situated in angle between. Marginal tentacles in 16 linear to outwardly-concave groups, 5-25 per group, each tentacle elliptical in section, with longitudinal canal and 2 rows of nematocyst warts on one side. Subumbrellar musculature weak, not prominent. Mouth-arm in length about 1/3-1/2 disc diameter, sides in form of convoluted curtains which may be lost. Stomach occupying slightly more than 1/3 of disc diameter, circular. Radial canals broad, typically wider than gaps between, margins irregularly sinuous in plan view; 16 rhopalial radial canals running to peripheral canal, forking several times, the branches continuing near-parallel with original canal to margin; inter-rhopalial canals typically 3-5, increasing in number during growth, straight but with sinuous sides, all reaching ring canal. Ring canal same width, sub-peripheral, in many specimens straight to bowed inwards in each of the 16 inter-rhopalial parameres. Peripheral to ring canal, rhopalial radial canals fork around rhopalia; inter-rhopalial radial canals continue nearly to margin of lappet. Occasional anastomosis in both rhopalial and inter-rhopalial canals, (?) especially in older individuals.
Coloration varied, perhaps partly consequent on diet. Recorded as milk-white disc and tentacles, with oral arms and gonads milky-white to lemon-yellow (Larson, 1986; Montsalve, 1996); radial canals orange/buff (P.F.S. Cornelius, pers. obs., Bay of Biscay); in formalin, exumbrella yellowish-milky, canal system milky/transparent, gonads dull orange to ochre, mouth-arms lighter (Mayer, 1910); disc milky-yellowish, gonads sepia (Mianzan, 1986b); disc colorless to bluish, canals and mouth-arms yellow, tentacles light violet, gonads reddish-brown (Naumov, 1961); stomach "brilliant orange, rest of disc colorless excepting yellow warts on lappets and on adjacent exumbrella" (Mills et al., 1996).