Tremaster mirabilis bends an arm to direct its gaze.MARIE HELENE BIRK, UNIVERSITY OF COPENHAGENSome animals that spend their whole lives in the dark—species of fish that thrive in caves, for instance—have dispensed with eyes all together. But in a study published today (February 7) in Proceedings of the Royal Society B, researchers have shown that several types of starfish that live in the deep ocean have working compound eyes at the tips of their arms, much like related species that dwell in shallower water.
“There’s been a lot of work over the years on vision in a variety of fish from shallow water to the deep sea, but there hasn’t been much at all done on vision in animals that sit on the bottom,” says Thomas Cronin, a biologist at University of Maryland, Baltimore County, who did not participate in the work. “It’s a been a question for a long time, what exactly are eyes used for down in these great depths?”
While earlier studies had shown that some starfish that live in shallower, brighter water have and use compound eyes, no one had previously looked at animals occupying the sea floor. “What you see in many other animal groups is that, when you venture deeper into the sea ...
