Several decades ago, scientists noticed that octopus skin did something strange. When researchers shone a bright light on it and then removed the light, chromatophores—tiny, circular pigment-filled structures—embedded in the skin would expand and then relax. Cephalopods such as squid, octopus, and cuttlefish use these chromatophores to dramatically change the color, shape, and texture of their skin, and scientists began to wonder if they could sense light as well. Now, two new studies have found evidence of rhodopsin—a light-sensitive protein usually in retinas—in the skin of cephalopods. Although most other mollusks, including scallops and snails, lack the cephalopods’ skill in shapeshifting, they can sense light with their skin, too. These findings, reported online today in The Journal of Experimental Biology, suggest that the light-sensing ability may have originated with an ancestral mollusk, which over time cephalopods have drafted to facilitate their unique behavior. The extent to which the ability contributes to their swift changes in appearance, however, remains unknown.
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