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I understand that the tube feet of an urchin contain photosensitive cells that allow the urchin to perceive its surroundings with what amounts to low-resolution vision. But does anyone know how far that "sight" extends? I put a tuxedo urchin in my RSM250 today, and right on a patch of nice, luxuriant algae, but was pretty amazed to see it rapidly crawl of the aquascape to my one clump of halymenia about a foot away. Which it then started to burrow into and/or eat. Coincidence? Super vision? Or do urchins rely on other senses to find food?