A shark’s version of the “inner light”?:
Scientists studying sharks off New Zealand have discovered that three deep-sea species glow in the dark – including one that is now the largest-known luminous vertebrate …
The kitefin, which can grow to 180cm, is now the largest-known luminous vertebrate: what researchers referred to as a “giant luminous shark” …
Researchers suggest these three species’ glowing underbellies may help camouflage them from any threats that might strike from beneath.
Elle Hunt, “‘Giant luminous shark’: researchers discover three deep-sea sharks glow in the dark” at The Guardian
But it turns out that the kitefin has no predators so the theory is that it uses bioluminescence for food or disguise.
The paper is open access.
Just how, exactly, and in response to what triggers do life forms develop bioluminescence? That would be something to research.
See also: In addition to other weird characteristics, the platypus has bioluminescent fur.
Convergent evolution: Squid bioluminescence evolved multiple times
One genus of fish eats bioluminescence from prey and displays it
More bioluminescents: