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Turns Out That 'Disco' Clams Also Come Armed with Toxic Snot

Just when you thought the Ctenoides ales couldn’t get weirder.
​Image: Jayvee Fernandez/Flickr

​Generally speaking, the more nicknames a species racks up, the more research it will inspire. But that hasn't been the case for the flashy mollusk Ctenoides ales—also known as the disco clam, the electric flame scallop and, most auspiciously, "king of the ocean."

The clam is so named because of the spectacular light show it can produce with its soft tissues, which is reminiscent of a disco ball or even a Tesla coil.

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The disco clam's flashy display. Credit: UC Berkeley Campus Life/YouTube.

But though Ctenoides ales has been marveled over for decades and is common throughout the Indo-Pacific, it wasn't until the summer of 2014 that the secret of its trademark radiance was finally decoded.

A team of biologists led by Berkeley's Lindsey Dougherty published an investigation into the luminous abilities of the clam in the June 25 issue of The Journal of the Royal Society Interface. "We don't know of anything that is quite like the disco clam," Dougherty told Nature at the time.

Indeed, the clam's crackling display, long assumed to be a bioluminescent adaptation, turned out to be something much more idiosyncratic. As Michael Byrne reported last summer, the species manufactures silica spheres capable of manipulating ambient light, as opposed to emitting new light, which is what bioluminescent organisms like fireflies and angler fish do. The feeding side of the clam's lip reflects light with nanoscale precision, while the opposite side absorbs light, giving it a reddish hue. The luminescent effect is produced by the rapid interaction of the two sides.

"To my knowledge, this reflectance from micro-silica in this critter, with a muscle-driven 'shutter' that creates rapid blinking, is unique," said Daniel Morse, a molecular biologist at the University of California, Santa Barbara, in the same Nature article.

Yesterday, Dougherty presented further findings on the clam's completely singular adaptation at the Annual Meeting for the Society for Integrative and Comparative Biology. Though most other luminescent organisms use light to lure in either prey or mates, Dougherty's team noticed that the clams used the brilliant display nearly twice as often when threatened predators, suggesting that the adaptation is defensive.

This theory was further corroborated by a punch-up between a mantis shrimp and a disco clam, in which the clam used sulfuric acid to protect itself. So not only does Ctenoides ales employ light as a deterrent, it also uses toxic mucus as a failsafe to that strategy.

Dougherty's research has reiterated that even the most eye-catching animals have untold complexities hidden in their biology. May 2015 bring many more insights into the behavior of the world's weirdest adaptations—though admittedly, the disco clam will be hard to top.