In the deep ocean, strange glowing sharks have developed eyes now capable of seeing complex patterns of light in the dark, according to a new study.
These bioluminescent sharks have a higher density of light sensitive cells in their retinas, and some species have even developed other visual adaptations to allow them to see the lights they use to signal each other, camouflage themselves, and find prey in this region where little light penetrates, according to a study published in the journal PLOS ONE.
"There are about 50 different shark species that are able to produce light - about 10 percent of all currently known sharks," said study researcher Julien Claes, a biologist at the at The Catholic University of Louvain in Belgium, according to Live Science.
The animals can live at a depth of about 650 to 3,300 feet, a dim location known as the mesopelagic twilight zone, which only weak sunlight can reach.
Claes and his colleagues recently showed that a number of species of bioluminescent sharks use a complex mechanism mainly involving hormones, compared to the brain signaling chemicals used by a number of glowing bony fishes.
Scientists are aware that the animals use their own light to camouflage themselves against predators under them by blending in with the sunlight, Claes said to Live Science.
He also discovered that some species have "light-saber" spines to fend off predators.
The sharks use light to recognize other members of their own species in order to find hunting partners or mates as well, according to the study.
For example, glowing lantern sharks possess light-producing structures on their sexual organs to help find each other in the dark, Claes said.
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