Chondrophore

Chondrophores are an order of hydrozoans, gelatinous Cnidarians superficially resembling jellyfish. The order, Chondrophora, is small: it contains a single family (Porpitidae) with just two genera and approximately six species in total. The most familiar members include the Blue Button (Porpita porpita) and the By-the-wind Sailor (Velella velella).

Although related to jellyfish, chondrophores are actually colonial animals made up of an orderly cooperative of polyps or chondrophores.

The tiny individual animals are specialized to perform specific tasks; some form the central gas-filled  disc (which is a golden brown colour and hardened by chitinous material) essential to keeping the colony afloat; others form radiating tentacles for tasks such as catching prey, reproduction, and digestion.

Velella species differ from Porpita species by their transparent, membranous sail-shaped floats; filled with gas, the membranes have a texture reminiscent of cellophane. Both genera have turquoise to dark blue mantles and tentacles, with lemon-yellow morphs occasionally encountered. Neither group is particularly large: the floats of Velellae are usually under 7.6 centimetres (3 inches) in diameter, while those of Porpita are usually less than 3.8 centimetres (1.5 inches). At the mercy of winds and currents, chondrophores are pelagic and drift in the open ocean. They are often seen in large aggregations; mass beachings are not unusual. Microplankton is a chondrophore's principal prey. Although none have stings, contact with the skin may cause irritation.

Chondrophores multiply by releasing tiny (0.3-2.5 millimetres or 0.01-0.09 inches) medusae which go on to develop new colonies. They are believed to have originated in the late Proterozoic period, some 650-540 million years ago.