Tardigrade

Tardigrades Temporal range: Turonian–Recent PreꞒ Ꞓ O S D C P T J K Pg N
Milnesium tardigradum, a eutardigrade
Echiniscus succineus, a heterotardigrade
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Subkingdom:	Eumetazoa
Clade:	ParaHoxozoa
Clade:	Bilateria
Clade:	Nephrozoa
(unranked):	Protostomia
Superphylum:	Ecdysozoa
(unranked):	Panarthropoda
Phylum:	Tardigrada Spallanzani, 1777
Classes
Eutardigrada Heterotardigrada Mesotardigrada (dubious)

Tardigrades ('water bears') are microscopic, segmented animals.^[1] They live in water. They are members of the tactopod phylum Tardigrada, part of the superphylum Ecdysozoa. They are also known as water bears or moss piglets.^[2][3]

Tardigrades were first described in 1773.^[4] Their name means "slow stepper". There are more than 1000 different species of tardigrade.^[5]

Tardigrades have a cylindrical shape with four segments, each with two legs. Each leg has little claws.^[5] The biggest adults may reach a body length of 1.2 mm, the smallest below 0.1 mm. Freshly hatched larvae may be smaller than 0.05 mm.^[4] Tardigrades feed on plant cells by penetrating the cell wall and eating what is inside. Some tardigrades are carnivores.^[6][5]

Tardigrades are eutelic: all adult tardigrades of the same species have the same number of cells. Some species have as many as 40,000 cells in each adult, while others have far fewer.^[7][8]

Tardigrades can be found in many habitats: in moss,^[6] freshwater,^[6] the Himalayas,^[4] and the ocean.^[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.^[5]

1. ↑ Neuman, Yair (October 2006). "Cryptobiosis: A new theoretical perspective". Progress in Biophysics and Molecular Biology. 92 (2). Elsevier: 258–267. doi:10.1016/j.pbiomolbio.2005.11.001. PMID 16380155.
2. ↑ Miller, William (2017-02-06). "Tardigrades". American Scientist. Archived from the original on 2018-04-14. Retrieved 2018-04-13.
3. ↑ Simon, Matt (21 March 2014). "Absurd Creature of the Week: the incredible Ccritter that's tough enough to survive in the vacuum of space". Wired. Archived from the original on 2014-03-25. Retrieved 2014-03-21.
4. ↑ ^{4.0 4.1 4.2 4.3 4.4} Riffenburgh, Beau (2007). Encyclopedia of the Antarctic. Vol. 1 (illustrated ed.). CRC Press. p. 983. ISBN 978-0-415-97024-2.
5. ↑ ^{5.0 5.1 5.2 5.3} Margulis, Lynn; Schwartz, Karlene V. (1998). Five kingdoms: an illustrated guide to the phyla of life on earth (illustrated ed.). Elsevier. p. 324. ISBN 978-0-7167-3027-9.
6. ↑ ^{6.0 6.1 6.2} "Tardigrade (animal)". Encyclopædia Britannica. Archived from the original on 2011-01-23. Retrieved 2011-01-02.
7. ↑ Seki, Kunihiro; Toyoshima, Masato 1998. Preserving tardigrades under pressure. Nature 395 (6705): 853–854. Preserving tardigrades under pressure | Nature Archived 2021-02-14 at the Wayback Machine
8. ↑ Kinchin, Ian M. 1994. The biology of tardigrades. Ashgate Publishing.