This video from California in the USA is called Disco Clams Light Up the Ocean Floor.
From Wildlife Extra:
The secret of the disco clam’s light show is revealed
The Ctenoides ales file clam, also known as the disco clam, is one of the few creatures to use silica micro-structures to reflect light, according to new research published in the Journal of the Royal Society Interface.
The clam does it so well that for years divers and scientists alike believed that it was generating its unique electric display with light-producing chemical reactions known as bioluminescence.
Lindsey Dougherty, a PhD student at the University of California, Berkeley, first shattered that idea last year with a series of presentations showing that the lips were lined with reflective silica spheres.
For the new study, Dougherty and her colleagues used an electron microscope to look at the spectral signature of the structure of the clam’s lip tissue.
Because red light doesn’t transmit well underwater, the dark side of the clams’ lips are effectively non-reflective.
Conversely, the silica-side reflects 85 to 90 per cent of all white light when underwater.
“They’re almost ideal reflectors in blue-green water environments,” said Dougherty.
The team confirmed this by using computer models to see how the spheres’ structures reflected light at four different wavelengths.
Using a high-speed camera, they were able to see exactly how the clams make the flash: by rapidly rolling and unrolling their lips, exposing the dark and reflective sides at a rate of about two times per second.
Disco clams can be found all the way from Australia to Indonesia in water from 10 to 160ft deep.
Even in shallow waters, the clams tend to squirrel themselves away into relatively dark nooks, which explains why it seemed so natural to think that their display was bioluminescent.
From an evolutionary perspective, lightning lips are a pretty costly adaptation. They need special muscles to control the furling motion, and silica is a rare element in the ocean.
Dougherty said there are three possibilities: The lips are to lure in mates, attract prey, or ward off predators.
In the future, she’s going to be researching the clams’ eyes (they have up to 40). Knowing how the clams see could unlock the secret behind their most prominent light-show feature.
See also here.