Cestum veneris has the standard ctenophore body plan pulled out of shape. The oral-aboral axis, which in a typical comb jelly runs from mouth to statocyst, is compressed, while the tentacular axis is drawn out into a ribbon that can pass a metre in length and only a few centimetres wide.
Four of the eight comb rows are reduced to short tracts near the sense organ; the other four run the length of the upper, aboral edge, so the diffraction shimmer travels the whole animal. Small tentacles line a groove along the lower margin and collect plankton, which is passed to the mouth at the ribbon's centre. Locomotion combines that ciliary beating with muscular undulation, a rippling motion most ctenophores lack, and the animal can accelerate away when disturbed.
The body is transparent and often faintly iridescent, and the species is bioluminescent, capable of a blue-green glow when disturbed at night. The name records how the animal looked to eighteenth-century naturalists: a belt or girdle. It is worth stressing that despite its appearance it is not a worm, not a jellyfish, and has no stinging cells.