Vision Systems
Sight evolved in innumerable organisms, many without any identifiable physical means to process vision.
Sea urchins are mobile pincushions, without a brain or eyes. Instead, a sea urchin is an eye, a very prickly one. Sea urchins have opsins scattered over their surface and on their feet. Though their mental images are rough, the urchin body-eye is good enough to tell light from dark and detect movement: sufficient to know when to put one’s spines up or run for cover.
