Pyrosoma

Pyrosoma, a genus of compound or colonial Tunicates, sometimes called 'fire-flames' on account of their brilliant phosphorescence. The colonies are hollow cylinders, open at one end, and the walls are formed of hundreds of individuals. These have inhalent apertures on the exterior, while their exhalent apertures open into the cavity of the cylinder, thus producing a gentle current, by means of which the colony is slowly propelled through the water with the closed end foremost. Several species occur in the warmer seas, and P. giganteum is from 2 to 3 feet long. See ASCIDIANS, PHOSPHORESCENCE.