Velella is a genus of free-floating hydrozoan, that live on the surface of the open ocean. Velella is commonly known by the names sea raft, by-the-wind sailor, purple sail, little sail, or simply Velella. Currently the only known and identified species is the Velella velella(shown above). Most are less than about 7cm long, they are usually deep blue in colour, but their most obvious feature is a small stiff sail that catches the wind and propels them over the surface of the sea. Under certain wind conditions, they may be stranded by the thousand on beaches.
Photo credit: Arne Saknussem