<Dd> Irradiation of tardigrade eggs collected directly from a natural substrate (moss) showed a clear dose - related response, with a steep decline in hatchability at doses up to 4 kGy, above which no eggs hatched . The eggs were more tolerant to radiation late in development . No eggs irradiated at the early developmental stage hatched, and only one egg at middle stage hatched, while eggs irradiated in the late stage hatched at a rate indistinguishable from controls . </Dd> <Ul> <Li> Environmental toxins--tardigrades are reported to undergo chemobiosis, a cryptobiotic response to high levels of environmental toxins . However, as of 2001, these laboratory results have yet to be verified . </Li> <Li> Outer space--tardigrades are the first known animal to survive in space . In September 2007, dehydrated tardigrades were taken into low Earth orbit on the FOTON - M3 mission carrying the BIOPAN astrobiology payload . For 10 days, groups of tardigrades were exposed to the hard vacuum of outer space, or vacuum and solar UV radiation . After being rehydrated back on Earth, over 68% of the subjects protected from high - energy UV radiation revived within 30 minutes following rehydration, but subsequent mortality was high; many of these produced viable embryos . In contrast, hydrated samples exposed to the combined effect of vacuum and full solar UV radiation had significantly reduced survival, with only three subjects of Milnesium tardigradum surviving . In May 2011, Italian scientists sent tardigrades on board the International Space Station along with extremophiles on STS - 134, the final flight of Space Shuttle Endeavour . Their conclusion was that microgravity and cosmic radiation "did not significantly affect survival of tardigrades in flight, confirming that tardigrades represent a useful animal for space research ." In November 2011, they were among the organisms to be sent by the U.S. - based Planetary Society on the Russian Fobos - Grunt mission's Living Interplanetary Flight Experiment to Phobos; however, the launch failed . Tardigrades are one of the few groups to have survived Earth's five mass extinctions . </Li> </Ul> <Li> Environmental toxins--tardigrades are reported to undergo chemobiosis, a cryptobiotic response to high levels of environmental toxins . However, as of 2001, these laboratory results have yet to be verified . </Li> <Li> Outer space--tardigrades are the first known animal to survive in space . In September 2007, dehydrated tardigrades were taken into low Earth orbit on the FOTON - M3 mission carrying the BIOPAN astrobiology payload . For 10 days, groups of tardigrades were exposed to the hard vacuum of outer space, or vacuum and solar UV radiation . After being rehydrated back on Earth, over 68% of the subjects protected from high - energy UV radiation revived within 30 minutes following rehydration, but subsequent mortality was high; many of these produced viable embryos . In contrast, hydrated samples exposed to the combined effect of vacuum and full solar UV radiation had significantly reduced survival, with only three subjects of Milnesium tardigradum surviving . In May 2011, Italian scientists sent tardigrades on board the International Space Station along with extremophiles on STS - 134, the final flight of Space Shuttle Endeavour . Their conclusion was that microgravity and cosmic radiation "did not significantly affect survival of tardigrades in flight, confirming that tardigrades represent a useful animal for space research ." In November 2011, they were among the organisms to be sent by the U.S. - based Planetary Society on the Russian Fobos - Grunt mission's Living Interplanetary Flight Experiment to Phobos; however, the launch failed . Tardigrades are one of the few groups to have survived Earth's five mass extinctions . </Li>

What is the most resistant form of life