Researchers at the Univeristy of Gothenburg have shown that sea urchins, although they have no eyes, can see with their whole body. The study was recently published in the scientific journal Proceedings of the National Academy of Sciences.
Most creatures with eyes react to light and process complex images to help them survive. Sea urchins can react to light without eyes. Previous studies on these creatures have shown that they have many genes linked to the development of the retina–the light sensitive tissue in human eyes. This implies that sea urchins contain genes that code for the eye protein, opsin.
“It was this discovery that underpinned our research,” said Sam Dupont, researcher and co-author of the article from the University of Gothenburg’s Department of Marine Ecology. “We wanted to see where the opsin was located in sea urchins so that we could find the sensory light structures, or photoreceptors. We quite simply wanted to know where the sea urchin sees from.”
The research group determined that the photoreceptors are located on the tip and base of the tube feet that are used for motion and located all over the sea urchin’s body.
“We argue that the entire adult sea urchin can act as a huge compound eye, and that the shadow that is cast by the animal’s opaque skeleton over the light- sensitive cells can give it directional vision,” says Dupont.
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