Claim: Tardigrades have been in at least one environment.

Tardigrades -LRB- -LSB- ˈtɑrdᵻˌgreɪd -RSB- also known as water bears , space bears , or moss piglets -RRB- are water-dwelling , eight-legged , segmented micro-animals . They were first discovered by the German zoologist Johann August Ephraim Goeze in 1773 . The name Tardigrada -LRB- meaning `` slow stepper '' -RRB- was given three years later by the Italian biologist Lazzaro Spallanzani . They have been found everywhere from mountaintops to the deep sea , mud volcanoes , and from tropical rain forests to the Antarctic .   Tardigrades are one of the most resilient animals known : they can survive extreme conditions that would be rapidly fatal to nearly all other known life forms . They can withstand temperature ranges from 1 K -LRB- close to absolute zero -RRB- to about 420 K for several minutes , pressures about six times greater than those found in the deepest ocean trenches , ionizing radiation at doses hundreds of times higher than the lethal dose for a human , and the vacuum of outer space . They can go without food or water for more than 30 years , drying out to the point where they are 3 % or less water , only to rehydrate , forage , and reproduce . Tardigrades living in harsh conditions undergo an annual process of cyclomorphosis .   They are not considered extremophilic because they are not adapted to exploit these conditions . This means that their chances of dying increase the longer they are exposed to the extreme environments , whereas true extremophiles thrive in a physically or geochemically extreme environment that would harm most other organisms .   Usually , tardigrades are about 0.5 mm long when they are fully grown . They are short and plump with four pairs of legs , each with four to eight claws also known as `` disks '' . The first three pairs of legs are directed ventrolaterally and are the primary means of locomotion , while the fourth pair is directed posteriorly on the terminal segment of the trunk and is used primarily for grasping the substrate . Tardigrades are prevalent in mosses and lichens and feed on plant cells , algae , and small invertebrates . When collected , they may be viewed under a very low-power microscope , making them accessible to students and amateur scientists .   Tardigrades form the phylum Tardigrada , part of the superphylum Ecdysozoa . It is an ancient group , with fossils dating from 530 million years ago , in the Cambrian period . About 1,150 species of tardigrades have been described . Tardigrades can be found throughout the world , from the Himalayas -LRB- above 6000 m -RRB- , to the deep sea -LRB- below 4000 m -RRB- and from the polar regions to the equator .