AP Photo

At the age of 21, snorkeling the clear, blue waters off Panama’s coast, Roger Hanlon caught his first glimpse of it. As the teenager scanned for vibrant sea life, his tall frame cast a shadow on an octopus below. Sensing danger, the creature blasted water at Hanlon before dashing off, its skin changing colors as it moved. First terrified, then intrigued, Hanlon chased the 1-pound mollusk for the next 20 minutes. “I just marveled at its changeable camouflage,” he says. “It moved along, fully exposed but really hard to see.”