See text Janthina is a genus of small to medium-sized pelagic or planktonic sea snails, marine gastropod molluscs in the family Epitoniidae.

[3] The adult snails prey upon (and live near to) one of several species of pelagic animals loosely known as jellyfish.

More specifically they eat the medusae of free-swimming Cnidaria, in particular the genus known as "by-the-wind sailors", Velella.

The snails are able to float securely because they create a raft of clear chitin around air bubbles formed near the ocean surface.

[4] The common names for this genus derive from the light purple or violet color of the shells and the violet-colored bodies.