Knowra Counterillumination Counterillumination Counterillumination is camouflage in which an animal emits light from its underside to match the brightness of the water above, reducing its silhouette when viewed from below.
Countershading : Camouflage in which an animal’s darker upper surface and lighter underside reduce the appearance of its three-dimensional shape. Unlike countershading’s fixed pigment pattern, counterillumination adjusts emitted light to changing conditions.
Lanternfish : A family of small deep-sea fishes known for rows of light-producing organs. Many lanternfish use ventral photophores to blend with downwelling light.
Mesopelagic zone : The ocean layer roughly 200 to 1,000 meters deep, where sunlight is faint and declines with depth. Its residual daylight creates the background counterilluminating animals must match.
Spectral sensitivity : The range of light wavelengths that a visual system can detect. Matching a predator’s visual background may require matching wavelengths, not brightness alone.
Photophore : A light-producing organ found in some animals, especially marine species. Photophores generate the underside light used to erase the animal’s silhouette.
Firefly squid : A small squid species, Watasenia scintillans, that produces bright blue bioluminescence. Its underside light can conceal its outline against the illuminated sea above.
Diel vertical migration : The daily movement of many marine organisms toward the surface at night and deeper water by day. Migrating animals encounter changing light levels that alter the demands of counterillumination.
Bioluminescence control : The physiological regulation of when, where, and how strongly an organism emits light. Precise control determines whether emitted light tracks shifting ambient conditions.
Bioluminescence : The production and emission of light by living organisms through chemical reactions. Counterillumination is a camouflage function of bioluminescence.
Hatchetfish : A deep-sea fish with a thin, laterally compressed body and light-producing organs on its underside. Its ventral photophores are adapted to match the faint light from the surface.
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