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Researchers at the University of California, Irvine, working with collaborators from the Marine Biological Laboratory (С����Ƶ) in Woods Hole, Massachusetts, have captured the first three-dimensional views of the cells that let longfin inshore squid (Doryteuthis pealeii) flip from glass-clear to vividly colored. 

The mantle of these Atlantic squid is packed with light-reflecting cells called iridophores (or iridocytes). Inside each iridophore, the team saw tightly coiled columns of protein reflectin. Acting like natural Bragg reflectors, these columns fine-tune how incoming light is scattered, allowing the animal to dial up brilliant hues on demand.

"The squid’s ability to rapidly and reversibly transition from transparent to colored is remarkable,” said study co-author Alon Gorodetsky, associate professor of chemical and biomolecular engineering at UC Irvine. “We found that cells containing specialized subcellular columnar structures with sinusoidal refractive index distributions enable the squid to achieve such feats.”

Gorodetsky’s group accessed the animals through senior С����Ƶ scientist and study co-author, Roger Hanlon. The С����Ƶ has spent more than a century dissecting cephalopod coloration and has provided key expertise on iridophore tissue structure.