Velella

Velella is a genus of chondrophores commonly known as by-the-wind sailors. They are small cnidarians that resemble a minature Portuguese man o' war. They are small, being typically about 30 mm across. They are usually blue in color, but their most obvious feature is a small stiff sail that catches the wind and propels them over the surface of the sea. In certain conditions they can become stranded on beaches in their thousands.

In common with other genera in this order, Velella are colonial animals that catch their prey, generally plankton, by means of cnidoblasts on fine retractable tentacles that hang down in the water. Though the toxins injected into their prey are very powerful, Velella are harmless to humans as they are unable to pierce the skin with their cnidoblasts.