Red brittle star ‘sees’ without eyes

The red brittle star captured scientific attention three decades ago thanks to its dramatic change in colour between day and night and its strong aversion to light.

Now scientists believe Ophiocoma wendtii, a relative to sea stars and sea urchins, has another trick up its sleeve.

Writing in the journal Current Biology, an international team led by Lauren Sumner-Rooney from Oxford University Museum of Natural History, UK, suggests O. wendtii uses colour change to navigate its way through coral reefs.

With colleagues from Germany’s Museum für Naturkunde, Lund University in Sweden, and the Georgia Institute of Technology, US, Sumner-Rooney ran hundreds of behavioural experiments to test the brittle stars’ “eyesight”.

“These experiments gave us not only the first evidence that any brittle star is able to see, but only the second known example of vision in any animal lacking eyes,” she says.

The animals were able to seek out areas of contrast, which the researchers think may mimic structures that could offer shelter from predators. 

Although it appears that their vision is very coarse, on the crowded tropical reefs disturbed brittle stars never have to look too far to make a dash for the nearest cover.

“It’s a very exciting discovery,” Sumner-Rooney says. “It had been suggested 30 years ago that changing colour might hold the key to light-sensitivity in Ophiocoma, so we’re very happy to be able to fill in some of the gaps that remained and describe this new mechanism.”