25. Cuttlefish
Cuttlefish have one of the most intriguing sleep cycles in the underwater world. While resting, they show REM-like sleep—their bodies twitch and their skin rapidly shifts color and pattern.
Scientists believe these vivid displays hint at complex dream-like activity, making cuttlefish sleep one of the great mysteries among cephalopods. Their strange and beautiful rest patterns continue to fuel curiosity about intelligence and sleep in ocean life. Live Science