Umbrella hemispherical when young (up to ca. 7 cm diameter), becoming gradually flatter with age, and at known maximun of 45 cm is inverted saucer-shaped, ca. 1/6 times as high as wide. Jelly flexible, thin. Exumbrellar surface with numerous, closely-packed low conical projections ca. 1 mm wide, barely visible and barely noticeable to finger-tip touch. Marginal lappets steep-sided triangular, clefts between rounded; ends of lappets in older specimens (above ca. 25 cm) possibly dividing to form additional lappets, but 4 inter-rhopalar lappets per octant in younger specimens. Rhopalar lappets tiny, parallel-sided, pointed. Rhopalia 8, white, peripheral, in deep clefts in margin. Subumbrellar musculature a continuous ring (unbroken over radial canals) of ca. 20 circular muscle-folds, in zone between ring canal and stomach. Mouth-arms in 4 pairs, laterally flattened basally, length ca. 2/3 disc diameter; proximal half laterally flattened, with mouthlets on inner side only; distal half 3-vaned, central vane and two laterals, mouthlets in band along the much-folded edges. Numerous thick filaments among the mouthlets, deciduous. Mouth-arm disc massive, 4 pillars supporting it, each broad-based, tapering slightly downward; the gaps between twice breadth of pillars. Stomach with outline of Maltese cross, the arms and corners rounded and broadened slightly peripherally; gonads rimming the stomach, cream to white; no central mouth. Eight rhopalar radial canals, all connecting to margin (contrary to Mayer, 1910); joined sub-peripherally by circular canal 1/3 of radial distance from margin (see diagrams in Vannucci, 1951; Mianzan, 1986b). From ring canal (in older specimens) typically 4 broad centripetal canals run part-way to stomach but do not connect with it; spaces between them slightly narrower than width of canals, some of which dilate just centripetal to ring canal. Extra-circular network fine, uniformly anastomosed; in some radii, continuation of rhopalar canal to periphery not immediately clear but typically just discernible; rhopalar radial canals broader internally to circular canal than between it and margin.
Color: exumbrella colorless to uniform very pale brown (36ºS, Argentina), or with varied density of elongate, variegated patches quite asymmetrically arranged, brown to pale brown (southern Brazil), in one published photograph (Caribbean, Humann, 1992) shown deep blue. Lappets slightly darker brown than exumbrellar patches, deep blue (even if exumbrellar patches brown). Mouth-arms colorless; region of mouthlets pale brown in some specimens, colorless in others.
Color variation is great. There is some variation in the centripetal canals, occasional ones being forked or joined to a neighbour. There is some variation also in the shape of inter-rhopalar lappets (see description), some apparently dividing from the four reported as usual in the species to form additional ones in older individuals, which have perhaps not often been examined in detail.