Although sea urchins don't have any problems avoiding predators or finding comfortable dark corners to hide in, they don't have eyes. The question then is how they see.
Genetic analysis of sea urchins has revealed they have light-sensitive molecules, mostly in their tube feet and in tiny stalked appendages found in among their spines. As such, "it looks like the entire surface of their bodies are acting as one big eye," said researcher Sönke Johnsen, a marine biologist at Duke University.
Scientists had conjectured the spines of sea urchins might then help them pick out relatively fine visual details by screening out light from off angles. If this proved true, urchins with densely packed spines would have relatively sharp vision.
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