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Diagram of a cephalopod's photophore, in vertical section. A photophore is a glandular organ that appears as luminous spots on marine animals, including 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 ...
When seen from below by a predator, the animal's light helps to match its brightness and colour to the sea surface above. Counter-illumination is a method of active camouflage seen in marine animals such as firefly squid and midshipman fish, and in military prototypes, producing light to match their backgrounds in both brightness and wavelength.
It is thought that this mode is to distract predators, analogous to chaff or flares dispensed from military aircraft during evasive maneuvers. Generally, gossamer worms grow to only a few centimeters in overall length, or 20 millimetres (0.79 in) to 40 millimetres (1.6 in) in total length, though this is likely to reflect the size of those ...
See also: phytochrome and phototropism. Most prokaryotes (bacteria and archaea) are unable to sense the direction of light, because at such a small scale it is very difficult to make a detector that can distinguish a single light direction. Still, prokaryotes can measure light intensity and move in a light-intensity gradient.
As such, counter-illumination camouflage can be seen as an extension beyond what countershading can achieve. Where countershading only paints out shadows, counter-illumination can add in actual lights, permitting effective camouflage in changing conditions, including where the background is bright enough to make an animal that is not counter ...
Predators need not locate their host directly: Kestrels, for instance, are able to detect the faeces and urine of their prey (which reflect ultraviolet), allowing them to identify areas where there are large numbers of voles, for example. This adaptation is essential in prey detection, as voles are quick to hide from such predators.
The more advanced infrared sense of pit vipers allows these animals to strike prey accurately even in the absence of light, and detect warm objects from several meters away. [ 2 ] [ 3 ] It was previously thought that the organs evolved primarily as prey detectors, but recent evidence suggests that it may also be used in thermoregulation and ...
These have light-producing organs (photophores) scattered all over their undersides, creating a sparkling glow that prevents the animal from appearing as a dark shape when seen from below. [11] Counter-illumination camouflage is the likely function of the bioluminescence of many marine organisms, though light is also produced to attract [ 12 ...