Strange glowing sharks have unique eye structure that helps them adapt and survive in the ‘twilight zone,’ of the deep ocean, a new study has revealed.
According to the researchers, the deep-sea bioluminescent sharks have evolved unique eyes that help them to see complex light patterns and that too in the dark.
The twilight zone is the area which is about 200-1000 meters under the sea. Even if the region is vast, it has dim habitat due to the unavailability of sunlight. In the absence of sunlight, point-like bioluminescent emissions takes their place in the deep sea.
The researchers carried a comprehensive mapping of the eye of five bioluminescent shark species and found that they possess higher rod densities of light-sensitive cells in their retinas than other sharks.
They also concluded that some species of sharks developed other visual adaptations that make them see the glimmering lights that are used to warn or alert each other in little light.
In order to better comprehend the bioluminescent predators inhabiting the ‘twilight zone’, the researchers studied the shape and structure of the shark’s eyes and also carried the retinal cell mapping to understand the visual systems of five deep-sea bioluminescent sharks, including one kitefin shark and four Lanternsharks.
Following the eye mapping, the scientists found that the eyes of the lantern sharks had a translucent region in their upper eye orbit. The scientists believe this translucent area may be responsible for counter-illumination adjustment or use bioluminescence to hide the fish. Several ocular specializations like the presence of a gap between lens and iris that allows penetration of extra light into the retina was also found. This was earlier unknown in sharks.
The study was published on Wednesday in the journal PLOS ONE.
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