The Violet Sea Snail (Janthina janthina) is a species of gastropod found in Britain.
A scarce vagrant to our shores from deep water, this species may wash up after storms, and is often associated with By-the-wind-sailors. Quite a large sea snail, this species has it's shell curled up and spherical, much like that of many land snails, but the shell is fragile. In deep water, this species floats by a raft of bubbles. The shell is a purple-white colour.