Is a state in which metabolic activities come to a reversible standstill. It is truly a death-like state; most organisms die by a cessation of metabolism. The most common type of cryptobiosis studied in tardigrades is anhydrobiosis
Tardigrades can survive dry periods by curling up into a little ball called a tun. Tun formation requires metabolism and synthesis of a protective sugar known as trehalose, which moves into the cells and replaces lost water. Revival typically takes a few hours, depending on how long the tardigrade has been in the cryptobiotic state.
Tardigrades have been found in the Antarctic and can survive temperatures as low as -200 °C (-328 °F). They can withstand freezing and/or thawing processes.
Water bears can survive temperatures as high as 151 °C (304 °F) and even exist in boiling alcohol.
On 14 September 2007 water bears made their first trip into space. In a project sponsored by the European Space Agency tradigrades were exposed to solar light (UV-radiation) in addition to space vacuum and cosmic radiation. Space vacuum and cosmic radiation did not affect their survival or reproduction at al.
Water bears can survive levels of X-ray radiation 1000x the lethal human dose.
A tardigrade can survive for decades or even longer; once immersed in water, the body returns to a normal metabolic state over the course of a few hours. One group of dehydrated tardigrades was reportedly taken from a museum sample of dried moss that was more than 100 years old and brought back to life.
They are are capable of withstanding pressures as powerful as 6,000 times that of the atmosphere which is equivalent to up to 6x the pressure of the deepest part of the ocean.