photophore

noun

An organ which emits light; the pattern of photophores is an important character in the identification of deepsea fishes. Light may be produced from compounds produced by the fish itself or from prey it has ingested, or by symbiotic bacteria. The organ may be simple or variously equipped with reflectors, lenses, shutters, etc., e.g. in Myctophidae, Gonostomatidae, Batrachoididae.