● Many sea creatures are bioluminescent​—that is, able to produce light. The clusterwink snail uses this ability in a unique way. When threatened by a predator crab, the clusterwink retreats into its shell and “flashes,” producing flickers of light that scare off the crab. But how does light shine through the snail’s shell?

Consider: Far from being a barrier, the shell of the clusterwink snail diffuses light. Dimitri Deheyn and Nerida Wilson, scientists at the Scripps Institution of Oceanography in San Diego, California, U.S.A., found that the light produced by the snail is uniformly spread throughout the entire shell, and the shell diffuses the light ten times more efficiently than a commercial diffuser of the same thickness (.02 inch; 0.5 mm). At the same time, the shell’s ability to transmit this light to its surroundings is eight times more efficient than man-made diffusers. Surprisingly, this extraordinary capability to diffuse or transmit light is not found in the shells of closely related nonbioluminescent marine snails. Not coincidentally, this light happens to be the color that travels the farthest in seawater.

Dr. Deheyn says that learning about the clusterwink snail “could be important for building materials with better optical performance.” The field of biophotonics, which uses light for medical analysis and treatment, also stands to benefit from such research. And in this era of light-emitting diodes, diffusers capable of more efficiently amplifying small light sources will doubtless contribute to energy savings.

What do you think? Did the shell of the clusterwink snail come about by evolution? Or was it designed?

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Magnified view of the shell in normal light

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Magnified view of the shell flashing diffused light

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Left: www.robastra.com; center and right: Courtesy of Dr. D. Deheyn, Scripps Institution of Oceanography, UC San Diego