Light bathes our planet, splashing off the mountaintops, flooding the deserts, tundra, savanna and forests, and seeping as deep as 1,000 meters into the ocean. Bacteria, plants, animals and all kinds of living things have evolved different ways to detect and respond to light. Despite their familiarity and prevalence, eyes are not essential.
Biologists have known for several decades that some eyeless animals perceive light. Likewise, some animals with eyes—even rather sophisticated eyes—rely on other body parts to see. Exactly how organisms sense light without eyes has, in many cases, remained mysterious. In recent years, with the help of new tools like genome sequencing, scientists have discovered light-sensitive cells and proteins in unexpected places, and have established that creatures once thought to be blind can in fact see. Light-reactive proteins cover the ends of a sea urchin's feet, for example, possibly turning the spiky animal's whole body into a compound eye. Similarly, tiny jellyfish-like hydras can sense light with their stinging tentacles. And although nematodes live in darkness underground, some of their neurons respond to light, helping them wriggle away from danger.
To read the original article: Blindsight: Animals That See without Eyes [Slide Show]: Scientific American
