Purple snails, not really something you think of. Janthina umbilicata, or Purple storm snails as they are more commonly known.
They are pelagic snails, this means that they spend all their time in open oceas, unless they are caught in a storm and washed on to beaches. These snails are tropical/subtropical and are not usually found far north.
They usually spend most there time upside down having produced a 'flotation device' made of bubbles. here is a video showing the snail making bubbles attaching them with mucus to make these folation devices.
So the next time someone tells you that snails are boring, tell them about the upside down purple snail!