According to records, the "little water bear worm" was first described by a priest named Gotze in 1773, but it was not complete. In 1774 and 1776, Italians Courtin and Spalanzani found that slow-moving animals can be "resurrected" without taking off their protective shells in a water-deficient environment.
Spallanzani also pointed out that slow-moving animals must slowly lose water if they want to survive the water shortage period. The name "slow-moving animals" was first given by Spallanzani. From the fossils of the water bear worm, we can know that this species existed as early as the Cambrian 500 million years ago.
Tardigrada is very small, the smallest is only 50 microns, and the largest is only 1.4 mm, which can only be seen clearly with a microscope. The body surface is covered with a water film to avoid drying and breathing oxygen in the water film.
They are very small, and most of them do not exceed 1 mm. Transparent, colorless, yellow, brown, crimson or green. Their colors are mainly determined by food. They eat foods containing carotenoids, which can be deposited in various organs.
They are composed of head, limbs and chitin stratum corneum. Four pairs of feet with claws, suckers or toes at the ends. There are two protrusions in front of the mouth, one for stabbing food and the other for absorbing tools. The foregut has many paired glands, and a thin esophagus connects the midgut.
Under the electron microscope, when the water bear worm is dry or the environment deteriorates, its body will shrink into a barrel shape, automatically dehydrate and quietly endure dormancy (dormancy phenomenon), which will show amazing endurance.
Therefore, slow-moving animals are considered to be the most vital animals. As far as cryptobiotics are concerned, they can generally survive at high temperature (151c), near absolute zero (the highest record is-272.8 c), high radiation, vacuum or high pressure for several minutes to several days. Cryptozoites of slow-moving animals have been recorded for more than 120 years.