Pyrosomata

a subclass of chordate animals of the class Thaliacea of the subphylum Tunicata. The Pyrosomata are free-swimming, colonial, marine animals. Although a colony usually does not exceed 20–30 cm in length, colonies of Pyrosoma spinosum in the Southern Pacific reach a length of 30 m. A colony resembles a hollow cyclinder. The wall of the colony, which has the transparency of glass, contains a single layer of thousands of identical zooids, which resemble ascidia (sea squirts) in structure. The mouth opening of each zooid opens to the outside, whereas the excretory aperture opens into the interior of the common cloaca of the colony. Near the pharynx is a pair of luminescent organs whose cells contain symbiotic bacteria capable of shining brightly in the dark. There are approximately 15 known species of Pyrosomata.