Disco clams create strobe light effects thanks to 'mirror balls' in their lips
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'Disco clams' were recently caught on camera 'partying' on the ocean floor while producing their own strobe light effects.
And now one scientist, who first came across the entertaining mollusc four years ago, has discovered the secret of how it lights up.
Ctenoides ales, dubbed disco clams because of this unique feature, produce the effect using its lips - which is packed with tiny spheres of reflective silica - like a mirror ball.
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Underwater raver: The disco clam - Ctenoides ales (pictured) - continually flashes light along the lip margins of its mantle - but no-one is sure why
THE DISCO CLAM'S PARTY MOVES
The strobe-light effect is produced when the clam rolls the edge of its mantle to expose a row of reflective cells.
When the clams are in a bright area of the ocean these cells reflect the light, making it look like it's coming directly from the clam.
The clams mainly reflect blue light, which can be seen further away in the ocean than other light wavelengths.
Lindsey Dougherty encountered the two-inch clam in 2010 while diving with her mother and sister in Wakatobi, Indonesia.
She saw Ctenoides ales roll the edge of its mantle - a layer of muscle and tissue that acts like a cloak over the mollusc's body - and produce a strobe-light effect using its mirrored lips.
Dougherty, a dive instructor and graduate student at the University of California, Berkeley, said: 'I've dived with humpback whales and great white sharks.
'But when I saw the disco clam, I was enamoured. I said then, "I'm going to do a PhD on the disco clam."'
Ctenoides ales are found in tropical areas of the Pacific Ocean, living in crevices in reefs, typically in clusters of two or more.
Light is dim and blue-green at the clams' typical depth, which ranges from 10-150 feet (3 to 50m) but their rippling mirrored lips are visible even without artificial illumination.
Lips like a disco ball: Scientist and driving instructor Lindsey Dougherty discovered that the mirrored lips are composed of packed nanospheres ideal for reflecting the blue light prevalent underwater. But she is not sure why the 'disco clams' (pictured) produce the light show
It didn't take long for the scientist to confirm that the flashing was not a form of bioluminescence, which is a chemical reaction inside animals like plankton that produces light similar to that of a glow stick.
Instead, she found, the edge of the clam's mantle lip is highly reflective on one side.
When the clam unfurls its lip - typically twice a second - the millimetre-wide mirror is revealed and reflects the ambient light, like a disco ball.
The inside of the clam's lip is packed with tiny spheres of silica, only 340 nanometers in diameter, that are ideal reflectors, particularly of the blue light that penetrates deeper into seawater compared to red light.
The outside of the lip contains no silica nanospheres, so when the lip is furled, no light is reflected, according to the study, published in the British Journal of the Royal Society Interface.
By repeatedly unfurling and furling the lip, the clam produces a continual rippling light show.
The non-reflective back of the lip strongly absorbs blue light, so it appears dark and makes the contrast between the sides even more striking.
A flashy 'dancer': It didn't take long for the scientist to confirm that the flashing (pictured) was not a form of bioluminescence - a chemical reaction inside animals like plankton that produces light similar to that of a glow stick. Instead, she found, the edge of the clam's mantle lip is highly reflective on one side
Ms Dougherty used high speed video, transmission electron microscopy, X-rays and computer modelling to study the detailed internal structure of the margin of the clam's lip, with help from other experts at Berkeley, Duke University and the University of Queensland.
She thinks that the 'disco clam' is alone in using silica nanospheres as flashing reflectors, but the white colour of several insects comes from a layer of silica that reflects white light.
While Ms Dougherty has revealed the mechanics of the mollusc's mirrored lips, she does not know why it flashes at all.
It is unlikely that it uses the light show to attract food as the clams are filter feeders, which means that they eat by straining matter and food particles from the ocean water through an internal filter.
Ms Dougherty also thinks it is unlikely that the display is designed to ward off predators, because there is nothing toxic or dangerous about the light.
There is a possibility that the disco lights are designed to entice a suitable mate.
Scientists are now studying all 40 of the clams' eyes, in order to see whether they can see their own light display.
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