photophore

thumb|300px|right|The elongate jewel squid (Histioteuthis reversa), so called because the photophores festooning its body make it appear bejewelled. thumb|300px|right|Diagram of a cephalopod's photophore, in vertical section.

A photophore is a specialized anatomical structure found in a variety of organisms that emits light through the process of bioluminescence. This light may be produced endogenously by the organism itself (non-symbiotic) or generated through a mutualistic relationship with bioluminescent bacteria (symbiotic), resulting in light production on a glandular organ of animals. Light organs are most commonly found in marine animals, including many species of fish and cephalopods. The organ can be simple, or as complex as the human eye, equipped with lenses, shutters, color filters, and reflectors; unlike an eye, however, it is optimized to produce light, not absorb it.