How does the 'disco clam' get down? Scientists unravel mystery.

You may have ditched your pet rock and polyester leisure suit, but there's a mollusc out there that is keeping the 1970s alive.

When it opens wide, the "disco clam" dazzles with flashes of bright light. Appearing at the "lip" of the animal's "mouth," this phenomenon is much like the effect of a disco ball.

Although some guessed that the flashes are an instance of bioluminescence, a kind of chemical reaction commonly seen in fireflies, glow worms, and many deep-sea creatures, this shellfish shimmers with a different kind of system.

The mechanism that the clam uses to create this illusion is reflective like the flashes of a disco ball, says University of California, Berkeley, graduate student Lindsey Dougherty.

A new study by Dougherty and other researchers revealed that the disco clam's lip scatters light. Just like the iconic mirrored ball, the clam's lip is made up of little spheres of silica packed tightly together. When light hits the lip's unfurling tissue, it reflects back in many directions.

Silica is known too for its ability to bend light. The silica spheres are close to the size that scatters light the best in the shorter wavelengths that the clams encounter in their natural environments, the researchers say. And being spheres, they scatter the light in all directions.

The other side of the clam's lip is red, and reflects light poorly. The clam rapidly furls and unfurls its lips, producing a dance-worthy strobe.

These clams live at depths of 10 to 150 feet below the ocean waters off Indonesia, Australia, and nearby. At these depths, the light is dim, but the disco clam's highly reflective lips can still be spotted.

Dougherty and her coauthors investigated this party-clam using a few different methods. They shined powerful lights on both sides of the clam's lip to measure reflection. Then they captured a high-quality, high-speed video of the disco mechanism in action.

Using an electron microscope, they examined the tissue and measured the size of the silicon spheres.  

Dougherty said in a news release that she still doesn't know why the clams put on such a light show. She is already exploring possible answers, such as repelling predators, attracting prey, or communicating with each other (the clams have 40 eyes, but it's unclear whether they are capable of seeing the flashes).

The disco clam, whose scientific name is Ctenoides ales, has a plain shell. But inside, the animal is fire-red with vermillion tendrils emerging from its hard home.

Dougherty discovered her first disco clam while diving off the coast of Wakatobi, Indonesia with her mother and sister in 2010. She recalls disco dancing underwater with her sister using the clam's flashing to set the rhythm.

A diving instructor who began diving when she was 14 years old, Dougherty was no stranger to charismatic marine animals. "I've dived with humpback whales and great white sharks," said Dougherty in a news release. "But when I saw the disco clam, I was enamored. I said then, 'I'm going to do a Ph.D. on the disco clam.'"