Velella is a genus of free-floating hydrozoans that lives on the surface of the open ocean, worldwide, and is commonly known by the names by-the-wind-sailor, purple sail, little sail, or simply Velella. The most common, and perhaps only species encountered is Velella velella. In common with other Cnideria, Velella are carnivorous animals. They catch their prey, generally plankton, by means of cnidocyst (also called nematocyst) -laden tentacles that hang down in the water. Though the toxins in their nematocysts are effective against their prey, Velella are harmless to humans, either because their nematocysts are unable to pierce or skin, or perhaps because humans do not react to the toxins encapsulated in their nematocysts. Nevertheless, it is probably wise not to to touch your face or eyes if you have been handling Velella.
Velella velella occur in warm and temperate waters in all the world’s oceans. They live at the water/air surface, with the float above water, and polyps hanging down about a centimeter below. Organisms that live partly in and partly out of water like this are known as “pleuston”. Offshore boaters are sometimes treated to seeing thousands of V. velella at a time on the water surface. Having no means of locomotion, V. velella are at the mercy of prevailing winds for moving around the seas, and are thereby also subject to mass strandings on beaches throughout the world.
Facts | Photo © John Walker