The strawberry squid, Histeoteuthis heteropsis, aka “the green-eyed squid” is a member of a group called “the cock-eyed” squids, so named because one eye is larger than the other. Scientists think that the smaller eye has evolved to look down, watching for predators from the depths. The bigger eye looks up, trying to detect the shadows of potential prey against the very faint light from above.
But, many animals in this midwater zone make their own light so they disappear in the faint light from above – called counterillumination. In the “survival game” of evolution, the strawberry squid’s much larger eye has evolved a lens with a fluorescent pigment that absorbs blue light. Researchers at the Monterey Bay Aquarium Institute think this allows the squid to detect prey whose counterillumination doesn’t quite match the color of the light from above. It’s that fluorescent pigment that appears green in the Remotely Operated Vehicle’s blue lights in the photo above.
This video from MBARI explains creatures of the deep use their own light and shows the green-eyed squid up-close and personal:
Read more about bioluminescence in the ocean
Read more about squid, octopuses and their kin