This cock-eyed squid can also counterilluminate. “If it’s, say, a little too green or a little yellow or something, it will stand out against a very black background,” and therefore be visible to the squid, explains Young. Check out the video above.)Īs the theory goes, the yellowish orb enables the squid to spy an animal above whose counterillumination doesn’t perfectly match blue, downwelling light. (The eye also fluoresces, but Haddock says that’s probably just a side effect of the pigment. That pigment acts as a filter for blue light, says Haddock. As the cephalopod’s big eye develops, the lens can become tinted yellow. The cock-eyed squid, however, has evolved an ability to detect animals that counterilluminate. Using light-emitting organs called photophores located along their body, these creatures can generate light that matches the color and intensity of downwelling sunlight, thereby obscuring their shadows. “By casting a shadow, giving their position away.”īut many midwater animals employ methods to escape detection, including a process known as counterillumination. “They live in a depth where there’s just some very faint light coming down,” says Young. While the small eye might watch for dangers emerging from the depths, the big eye-which can better detect details-looks upward, where it can catch sight of shadows cast by prey swimming above, according to Richard Young, emeritus professor of oceanography at the University of Hawaii. “It’s thought that each eye serves a different function,” says Haddock. Cock-eyed squid (Histioteuthis heteropsis). The members of the cock-eyed squid family are the only squids known for such distinctive oculi. This is a species of cock-eyed squid, whose scientific name, Histioteuthis heteropsis, means “different eyes.” “They have that one eye that looks about proportional to the body, and then the other eye is about twice the diameter on the other side,” says Steven Haddock, a marine biologist at the Monterey Bay Aquarium Research Institute. In the midst of “the twilight zone”-the ocean realm ranging from 200-1,000 meters below the surface-roams this small cephalopod. A cock-eyed squid known as the "strawberry squid." Photo by Steven Haddock
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