Cryptobiosis is a reversible state in which an animal's metabolism has come to a virtual standstill. Cryptobiosis is exhibited by various types of organism, including the tardigrade (shown here). A tardigrade, or "water bear," can go into a hibernation mode, known as the tun state, that is more akin to suspended animation whereby it can survive temperatures from -253°C to 151°C, as well as exposure to X-rays, and vacuum conditions. When tardigrades are placed in perfluorocarbon fluid (again while hibernating), at a pressure of 600 megapascals (MPa) – almost 6,000 times atmospheric pressure at sea level – they emerge from the experience unharmed. See also cryobiology.