Tardigrades were firstdescribed in 1773.[4] While originally namedKleiner Wasserbär (little waterbear) by zoologist Johann August Ephraim Goeze, the name "Tardigrade" was later given in 1777, by biologist Lazzaro Spallanzani, with the name meaning "slow stepper".[5] There are more than 1000 differentspecies of Tardigrade.[6]
Tardigrades have acylindrical shape with foursegments, each with two legs. Each leg has littleclaws.[6] The biggest adults may reach a body length of 1.2 mm, the smallest below 0.1 mm. Freshly hatchedlarvae may be smaller than 0.05 mm.[4] Tardigrades feed onplantcells bypenetrating thecell wall and eating what is inside. Some tardigrades arecarnivores.[7][6]
Tardigrades areeutelic: all adult Tardigrades of the same species have the same number ofcells. Some species have as many as 40,000 cells in each adult, while others have far fewer.[8][5]
Tardigrades can be found in manyhabitats: inmoss,[7]freshwater,[7] theHimalayas,[4] and theocean.[4] They are one of the few animals that can be found on the highest mountains and the deepest seas.[4] About 83% of the known species live on land, the other 17% live in water.[6]
Tardigrades can survive more than ten years withoutwater.[14] Tardigrades can survive extreme temperatures. They can live for a few hours intemperatures close toabsolute zero[7] and aboveboiling point.[14] They can survive a few minutes in temperatures as high as 151 °C (304 °F).[15][16] Some Tardigrades can survive being frozen for over 30 years.[17]
In 2019, alander with Tardigrades on board crashed on themoon. It is believed that the Tardigrades survived and could live for a few years on the moon.[22][23]
The Tardigrades slow theirmetabolism to survive these environments.[24]Rotifers have a similar agility to survive.
↑Horikawa, Daiki D (2012). "Survival of Tardigrades in Extreme Environments: A Model Animal for Astrobiology". In Altenbach, Alexander V.; Bernhard, Joan M.; Seckbach, Joseph (eds.).Anoxia. Cellular Origin: life in extreme habitats and astrobiology. Vol. 21. pp. 205–17.doi:10.1007/978-94-007-1896-8_12.ISBN978-94-007-1895-1.
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