Two studies — one on squid and cuttlefish, another on octopuses — published in the Journal of Experimental Biology on 15 May demonstrate that the skin of colour changing cephalopods harbors molecules used in vision, perhaps explaining how the organ detects light. In the case of squid and cuttlefish, researchers from University of Maryland Baltimore County and the Marine Biological Laboratory in Woods Hole, Massachusetts, found that the animals’ chromatophores — the cells that stretch out to expose their colourful pigment or pinch in to hide it — express opsins.

And in the octopus study, scientists at the University of California, Santa Barbara, observed that illuminating a patch of skin caused the chromatophores to expand. In octopuses, however, it was the cilia that contained opsins. “(Our) data suggest that a common molecular mechanism for light detection in the eyes may have been co-opted for light sensing in octopus skin and then used for Light-Activated Chromatophore Expansion,” M Desmond Ramirez and Todd Oakley of UC Santa Barbara wrote in their report on octopuses.

“All the machinery is there for them to be light-sensitive but we can’t prove that. It&’s been very frustrating,” Tom Cronin, a vision researcher at the University of Maryland who was part of the squid and cuttlefish study, told National Geographic&’s Not Exactly Rocket Science. “We don’t know if they contribute to camouflage or are just general light sensors for circadian cycling or are driving hormonal changes. They have a job to do but we don’t know what it is.”