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Tardigrades (/ ˈ t ɑːr d ɪ ɡ r eɪ d z / ⓘ), [1] known colloquially as water bears or moss piglets, [2] are a phylum of eight-legged segmented micro-animals. They were first described by the German zoologist Johann August Ephraim Goeze in 1773, who called them Kleiner Wasserbär ' little water bear ' .
Tardigrades, which are eight-legged micro-animals, are commonly referred to as water bears or moss piglets and are found all over the world in varying extreme habitats. First discovered in 1904 and originally named Hypsibius antarcticus, Acutuncus antarcticus is the most abundant tardigrade species in Antarctica. [1]
Tardigrades can withstand 1,000 times more radiation than other animals, [17] median lethal doses of 5,000 Gy (of gamma rays) and 6,200 Gy (of heavy ions) in hydrated animals (5 to 10 Gy could be fatal to a human). [18] Earlier experiments attributed this to their lowered water content, providing fewer reactants for ionizing radiation. [18]
Tardigrades have been shown to respond to different temperature changes at different developmental stages. Specifically, the younger the egg, the less likely it is to survive extreme environments. However, not too long after development, tardigrades demonstrate a remarkable ability to withstand these conditions.
Tardigrades are known to exist in almost every biome on the earth. There are terrestrial species, marine species, and even fresh water species have been found. [4] The eight currently recognized species in the genus Bertolanius Özdikmen have a wide distribution ranging from colder arctic areas, including Norway and Sweden, to more temperate regions like the Mediterranean. [2]
Panarthropoda is a proposed animal clade containing the extant phyla Arthropoda, Tardigrada (water bears) and Onychophora (velvet worms). [3] Panarthropods also include extinct marine legged worms known as lobopodians ("Lobopodia"), a paraphyletic group where the last common ancestor and basal members of each extant panarthropod phylum are thought to have risen.
Milnesium tardigradum can be found worldwide and is one of the biggest species among tardigrades (up to 1.4 mm); similar-looking species have been found in Cretaceous amber. [1] The mouth of this predator has a wide opening, so the animal can eat rotifers and larger protists. Other eutardigrades belong to the order Parachela.
Ramazzottius is a genus of water bear or moss piglet, a tardigrade in the class Eutardigrada, named after the Italian zoologist Giuseppe Ramazzotti.. Ramazzottius varieornatus (see image) is a terrestrial invertebrate that is extroardinarily tolerant of extreme conditions such as irradiation, chemicals, dehydration and high pressure. [2]