photophores

Photophore (plural photophores) is a light-emitting organ found in many bioluminescent animals, especially marine species such as cephalopods, fishes, crustaceans, and cnidarians. Photophores may be intrinsic light-producing tissues or host symbiotic luminous bacteria. Their size, shape, and placement vary widely among species, ranging from a single organ to multiple fields arranged along the body or fins.

Light production occurs in two main ways. In intrinsic photophores, light is generated by photogenic cells containing luciferin and luciferase, or other luciferin-luciferase-like systems, with neural or hormonal control. In bacterial photophores, luminescent bacteria reside in dedicated light chambers; the host supplies oxygen and substrates and can regulate emission. Emission is often directed by lenses, reflectors, and pigmented shields to create focused beams and prevent unwanted glare.

Functions of photophores include counter-illumination to hide silhouettes from predators below, camouflage, and signaling for mating, schooling, and prey attraction. The patterns and intensity of photophore light are often species-specific and can convey information to conspecifics.

Photophores are widespread among deep-sea fishes (notably lanternfishes), squid, octopods, and crustaceans, with ventral or dorsal distributions tailored to their ecological roles. Some taxa rely on bacterial symbionts, while others produce light autonomously.

Photophore systems illustrate convergent evolution of bioluminescence and host–microbe interactions and have been central to studies of deep-sea ecology and bioluminescent signaling.