Temporal range: Cambrian–Recent[1]
SEM image of Milnesium tardigradum in active state - journal.pone.0045682.g001-2.png
Milnesium tardigradum
Scientific classification edit
Spallanzani, 1777

Tardigrades (d/; also known colloquially as water bears, or moss piglets)[2][3][4][5] are a phylum of water-dwelling, eight-legged, segmented micro-animals.[2][6] They were first described by the German zoologist Johann August Ephraim Goeze in 1773, who gave them the name of "little water bears". The name Tardigrada (meaning "slow steppers") was given three years later by the Italian biologist Lazzaro Spallanzani.[7] They have been found everywhere: from mountaintops to the deep sea and mud volcanoes;[8] from tropical rain forests to the Antarctic.[9] Tardigrades are among the most resilient known animals,[10][11] with individual species able to survive extreme conditions that would be rapidly fatal to nearly all other known life forms, such as exposure to extreme temperatures, extreme pressures (both high and low), air deprivation, radiation, dehydration, and starvation. About 1,150 known species[12][13] form the phylum Tardigrada, a part of the superphylum Ecdysozoa. The group includes fossils dating from 530 million years ago, in the Cambrian period.[14]

Usually, tardigrades are about 0.5 mm (0.02 in) long when they are fully grown.[2] They are short and plump, with four pairs of legs, each ending in claws (usually four to eight) and/or sucking disks.[2][15] 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.[16]


Johann August Ephraim Goeze originally named the tardigrade kleiner Wasserbär (Bärtierchen today), meaning "little water bear" in German. The name Tardigradum means "slow walker" and was given by Lazzaro Spallanzani in 1776.[17] The name "water bear" comes from the way they walk, reminiscent of a bear's gait. The biggest adults may reach a body length of 1.5 mm (0.059 in), the smallest below 0.1 mm. Newly hatched tardigrades may be smaller than 0.05 mm.

SEM image of Hypsibius dujardini

The most convenient place to find tardigrades is on lichens and mosses. Other environments are dunes, beaches, soil, and marine or freshwater sediments, where they may occur quite frequently (up to 25,000 animals per litre). Tardigrades, in the case of Echiniscoides wyethi,[18] may be found on barnacles.[19] Often, tardigrades can be found by soaking a piece of moss in water.[20]

Other Languages
Afrikaans: Waterbeertjie
Alemannisch: Bärtierchen
አማርኛ: የውሃ ድብ
العربية: بطيء الخطو
azərbaycanca: Ərincəklilər
تۆرکجه: سۇ آییلاری
беларуская: Ціхаходкі
беларуская (тарашкевіца)‎: Ціхаходкі
български: Бавноходки
català: Tardígrads
Cebuano: Tardigrada
čeština: Želvušky
Cymraeg: Arafsymudwr
dansk: Bjørnedyr
Deutsch: Bärtierchen
eesti: Loimurid
Ελληνικά: Βραδύπορα
español: Tardigrada
Esperanto: Tardigradoj
euskara: Tardigrada
فارسی: خرس آبی
français: Tardigrada
Gaeilge: Béar uisce
galego: Tardígrados
한국어: 완보동물
հայերեն: Ջրային արջ
hrvatski: Dugoživci
Bahasa Indonesia: Tardigrada
interlingua: Tardigrada
íslenska: Bessadýr
italiano: Tardigrada
ქართული: ნელამავალნი
қазақша: Жайбасар
Kiswahili: Kidudu-dubu
кырык мары: Мызыргышывлӓ
Latina: Tardigrada
latviešu: Gauskāji
lietuvių: Lėtūnai
Limburgs: Beerbieskes
മലയാളം: ടാർഡിഗ്രാഡ
Nederlands: Beerdiertjes
日本語: 緩歩動物
Nordfriisk: Beerdiarten
norsk: Bjørnedyr
norsk nynorsk: Bjørnedyr
occitan: Tardigrada
پنجابی: پانی رچھ
Plattdüütsch: Waterboren
polski: Niesporczaki
português: Tardigrada
română: Tardigrada
русский: Тихоходки
Simple English: Tardigrade
slovenčina: Pomalky
slovenščina: Počasniki
српски / srpski: Водени медвед
srpskohrvatski / српскохрватски: Dugoživci
svenska: Trögkrypare
Tagalog: Tardigrada
татарча/tatarça: Әкрен йөрүчеләр
Türkçe: Su ayıları
українська: Тихоходи
Tiếng Việt: Gấu nước
Winaray: Tardigrada
Lingua Franca Nova: Tardigrado