The body of purple sea urchins may allow spatial vision due to diffuse photoreceptors on the body surface and spines that shield wide-angle light.

“Sea urchins don’t seem to have any problems avoiding predators or
finding comfortable dark corners to hide in, but they appear to
do all this without eyes. So how do they see? It appears that
sea urchins may use the whole surface of their bodies as a
compound eye, and the animals’ spines may shield their bodies from
light coming from wide angles to enable them to pick out relatively
fine visual detail.” (Knight 2010:i-a)

Last Updated August 18, 2016