This close-up photo shows the tough, serrated ring around the opening of a giant squid sucker. The ring is made of chitin—the same material that’s in your fingernails. Using suction, the sucker tightly grips the squid’s prey. The ring digs into the skin of the giant squid’s only predator—the sperm whale—leaving its mark behind. More about the giant squid can be found in our Giant Squid featured story.