An octopus can sense light through its skin, without using its eyes

Cut a small patch of skin from an octopus or squid and shine light on it in a dish, and the pigment cells will still respond — because their skin is packed with the same light-sensitive proteins found in eyes. Researchers think this lets an octopus's whole body help it match its surroundings, sensing light even on the parts it can't see.

— M. Desmond Ramirez & Todd H. Oakley, Octopus — Journal of Experimental Biology, 2015