The specific name, flavoanulatus refers to the yellow subapical ring of the cerata (from the Latin words flavus, yellow and anulatus, ringed). The body and the cerata of Janolus flavoanulatus are translucent, the latter with a purple subapical ring merging towards the tip into bright blue, and a yellowish ring below the purple ring. The rhinophores are brown-reddish with white tips. The caruncle is pale yellowish/cream. There is a bluish margin to the foot, the 'tail' is blue.