<p><strong>Nerve cells—dyed red in the above image—are responsible for squids' shimmering displays of iridescence, new research shows.</strong></p><p>A squid's shifting metallic sheen comes from clusters of tiny platelike structures inside their skin cells. (See <a href="http://ocean.nationalgeographic.com/ocean/photos/squid/">squid pictures</a>.)</p><p>Known as iridophores, the microscopic ensemble interferes with the way certain wavelengths of light are reflected.</p><p>"It's the same effect you get with shiny colors on a soap bubble or a thin layer of oil on the water surface in a harbor," said study co-author <a href="http://hermes.mbl.edu/mrc/hanlon/people.html">Paloma Gonzalez-Bellido</a>, a neuroethologist at the Marine Biological Laboratory in Woods Hole, Massachusetts.</p><p>Exactly how squid turn these iridophores on and off has, until now, remained a mystery.</p><p>A new technique allowed the team to hook up electrodes to individual nerves in squid skin. When they sent electrical impulses into the nerves, the iridophores changed color and brightness.</p><p>(See <a href="http://news.nationalgeographic.com/news/2010/07/100729-jumbo-squid-giant-bite-video-science-humboldt/">"Jumbo Squid Flash, Flail in First Ever Squid-cam Video."</a>)</p><p><em>—Helen Scales</em></p>