How brittlestars ‘see’ without eyes

By Giorgia Guglielmi

Seeing doesn’t always take eyes. The brittlestar Ophiocoma wendtii, a relative of starfish, can scan the sea floor, thanks to light-sensitive cells scattered across its skin, rather than by using eye-like structures, a study suggests.

The research, published on 24 January in Proceedings of the Royal Society B1, upends a long-standing hypothesis about how Ophiocoma sees its surroundings.

Although it has no brain, this reef-dwelling animal — consisting of five arms joined to a central disk — can detect light and move away from it. Ophiocoma’s skeleton, which is draped in a thin layer of skin, is covered in bead-like crystal structures, which scientists thought worked together as a big compound eye. By focusing light onto nerve bundles that researchers thought ran below these ‘microlenses’, the arrangement would allow the animal to form an image2.

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