Sea urchins have no eyes but they sense light and dark and direction of movement. A large number of genes that are used to build the retina have previously been found in urchins even though there was no eye structure. This new study located those retina genes (including one coding for opsin) at the tips and base of all those spiny tube feet. When Mom warned her kids she had eyes in the back of her head, she had no idea how outclassed she was by a sea urchin whose whole body interprets light.
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