The class Heterotardigrada includes tardigrades that have cephalic appendages and legs with four separate but similar digits or claws on each. 444 species have been described.
Aysheaia is an extinct genus of soft-bodied lobopodian, known from the Middle Cambrian Burgess Shale of British Columbia, Canada
Opilioacaridae is the sole family of mites in the order Opilioacarida, made up of about 13 genera. The mites of this family are rare, large mites, and are widely considered primitive, as they retain six pairs of eyes, and abdominal segmentation. They have historically been considered separate from other mites belonging to Acariformes and Parasitiformes, but are now generally considered a subgroup of Parasitiformes based on molecular phylogenetics.
Marine invertebrates are the invertebrates that live in marine habitats. Invertebrate is a blanket term that includes all animals apart from the vertebrate members of the chordate phylum. Invertebrates lack a vertebral column, and some have evolved a shell or a hard exoskeleton. As on land and in the air, marine invertebrates have a large variety of body plans, and have been categorised into over 30 phyla. They make up most of the macroscopic life in the oceans.
Tardigrades, known colloquially as water bears or moss piglets, 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. In 1777, the Italian biologist Lazzaro Spallanzani named them Tardigrada, which means "slow steppers".
Hypsibius dujardini sensu lato is a species complex of tardigrade in the class Eutardigrada. A member of this complex, Hypsibius exemplaris, is widely used for various research projects pertaining to evolutionary biology and astrobiology.
Echiniscus testudo is a cosmopolitan species of tardigrade.
Parachela is an order of tardigrades in the class Eutardigrada. Members of this order have existed for at least 72 million years, including the present. The oldest known species is Beorn leggi.
Milnesium is a genus of tardigrades. It is rather common, being found in a wide variety of habitats across the world. It has a fossil record extending back to the Cretaceous, the oldest species found so far is known from Turonian stage deposits on the east coast of the United States.Milnesiums are one of the most desiccation and radiation-resistant invertebrates on Earth because of their unique ability to transform into a "tun" state and utilize intrinsically disordered proteins when experiencing extreme environments.
Tactopoda or Arthropodoidea is a proposed clade of protostome animals that includes the phyla Tardigrada and Euarthropoda, supported by various morphological observations. The cladogram below shows the relationships implied by this hypothesis.
Richtersius is a monospecific genus of tardigrades in the family Richtersiidae; its sole species is Richtersius coronifer. R. coronifer is one of two species of tardigrade that have been shown to survive and continue reproducing after exposure to outer space, specifically in the thermosphere at 258–281 km above sea level with ionizing solar and galactic cosmic radiation for 10 days. However, unlike Milnesium tardigradum, R. coronifer did not survive under these conditions plus UV exposure.
Milnesium antarcticum is a species of Eutardigrades in the family Milnesiidae. This species differs from its cogenerate species mainly by proportions of its claws and buccopharyngeal apparatus.
Beorn leggi is an extinct species of tardigrade and the first known fossil tardigrade, discovered c. 1940 and described in 1964 from Late Cretaceous amber from Manitoba, Canada. It is the only species in the genus Beorn, and family Beornidae. It is one of two fossil tardigrades known from the Cretaceous, the other being Milnesium swolenskyi from the Turonian New Jersey amber.
Dsup is a DNA-associating protein, unique to the tardigrade, that suppresses the occurrence of DNA breaks by radiation. When human HEK293 cells were engineered with Dsup proteins, they showed approximately 40% more tolerance against X-ray radiation.
Macrobiotus shonaicus is a species of tardigrade in the family Macrobiotidae. As of 2018 it is only known from its type locality: Tsuruoka, Japan. The species description was published in 2018. The insides of their first three pairs of legs have a slight fold above their claws, and their eggs have processes whose terminal discs split off into thin filaments.
Milnesium swolenskyi is a species of tardigrade from the Cretaceous period. It, Beorn and Paradoryphoribius are the only known tardigrade genera in the fossil record. The type specimen AMNH NJ-796 was found in Turonian New Jersey amber, from about 93.9 to 89.8 million years ago (mya).
Bertolanius is a genus of tardigrades belonging to the family Eohypsibiidae.
Milnesium alpigenum is a species of tardigrade that falls under the Tardigrada phylum. Like its taxonomic relatives it is an omnivorous predator that feeds on other small organisms, such as algae, rotifers, and nematodes. M. alpigenum was discovered by Christian Gottfried Ehrenberg in 1853. It is very closely related to Milnesium tardigradum along with many other species from the Milnesium genus.
Milnesium lagniappe is a species of Eutardigrade in the family Milnesiidae. It is found in the southeastern United States, where it grows on lichens and plant litter. This microscopic creature belongs to the Milnesium granulatum species complex and is characterised by its claw formula, distinct cuticle features and stout claws with well-developed accessory points.
