The tardigrades (Filum Tardigrada, commonly called water bears, due to its appearance and the slowness in its 41 movements; they constitute a phylum in the animal Kingdom, characterized as invertebrates, protostomos, segmented and microscopic ( 0.1 to 1.2 mm ) Are also grouped within the large group Parartropodos by presenting characters that suggest that they share a common ancestor with arthropods, next to the Onicoforos.los tardigrades were described for the first time by Johann August Ephraim Goeze in 1773, which named them as water 40 bear; the Kleine Wasser-Bären German, literally " water 34 bears; ) and it refers to the way in which step, similar to the gait of a bear. Later, the term Tardigrado ( which means " slow step " ) It was given by Lazzaro Spallanzani in 1777 precisely because of the slowness of this animal.They possess unique in the animal Kingdom characteristics such as to survive in the vacuum of space, very high pressures - 6000atm (The atmospheric pressure at the Earth's surface is of 1atm, by which they can resist 6000 times more atmospheric pressure ) to prolonged dehydration ( up to 10 years can pass without getting water ) or ionizing radiation.