Worldwide seas, mostly warm, mostly in the Atlantic area. Rare in Mediterranean. Pleustonic floating predator, sometimes attached to the Hydrozoa which it feeds on, more often found on the underside of a bubble-raft it secretes. Original taxon: Helix janthina. As the shape varies and as the species was discovered in many places, the list of synonyms is impressive.

One synonym is bicolor Menke, because of the difference between the top of the shell (usually pale, like the sky seen from below by a fish or a turtle) and its bottom (darker, like the sea when it is seen from above, by a bird for example). This countershading is a kind of camouflage that is fairly common in some marine animals such as killer whales, sharks…

The species in H.-M. D. de Blainville: Manuel de malacologie et de conchyliologie vol. II, Paris 1827, plate XXXVIIbis fig.1a. The drawing highlights the subcarinate profile of the last whorl, as well as the colour difference between the top and the bottom.