photophore

A photophore is a light-emitting organ found in a variety of marine organisms, most prominently in deep-sea fishes, cephalopods, and some crustaceans. Light production in photophores may arise from intrinsic biochemical reactions within photocytes or from luminescent bacteria housed inside the organ. In the latter case, the bacteria typically provide the light, while the host provides a sheltered environment and control over emission.

Anatomically, photophores can be simple or highly elaborate. They generally include light-producing tissue, a means of directing or shaping the emitted light (such as lenses, prisms, or reflective surfaces), and a covering or shutter that the animal can open or close to modulate intensity. The arrangement of photophores along the body varies by species and can form ventral, dorsal, or lateral patterns that are useful for communication or camouflage.

Functions of photophores are diverse. A primary role in many fish is counter-illumination: producing light on the ventral surface to erase silhouettes when viewed from below, aiding camouflage in the open ocean. They also serve intraspecific signaling and mate recognition, lure or attract prey, and, in some cases, help deter predators or intimidate rivals.

Photophores are widespread in marine environments, especially among organisms adapted to dim or deep habitats. Notable groups with extensive photophore systems include lanternfishes and dragonfishes, with additional examples in certain squids and other cephalopods. Research into photophores informs taxonomy, ecology, and the study of bioluminescence mechanisms.