This Velella velella is the only creature known of its kind.
Wiki writes about this: http://ru.wikipedia.org/wiki/Velella_velella
Velella velella (lat.) Is a colonial representative of hydroids, an oceanic pelagic species. The only representative of the genus.
Velella velella is not an independent organism, but a colony of hydroids.
Inside the colony, a flat, air-filled chamber of chitin is formed that is covered with a mantle. It is she who ensures the maintenance of the entire colony on the surface of the water. The base of the colony is an oval reinforced with chitinous structures. A characteristic feature of the species is a thin semicircular blade located at the top of the diagonal of the air chamber. Above the base there is a sail, which is located asymmetrically and is curved in the shape of the letter S. Thanks to this blade, the animal received its name (from the Latin "velum" - sail). This outgrowth allows animals to move along the surface of the water not in a straight line, but at a certain angle to the wind, periodically turning 180 degrees. Colony size can reach 10 centimeters (usually about 7 cm). The tentacles are filiform, relatively short, hanging from the air chamber. Their number varies from 8 or more.
Colony-forming polyps have different shapes and specializations . There is a prominent central polyp of large size, which is a gastrozoid (specializing in catching and digesting food). It is surrounded by gastro-gonozooids (polyps that specialize in feeding and reproduction) and dactylozooids (polyps that specialize in protective function)