They have been found in diverse regions of Earth's
biosphere – mountaintops, the
deep sea,
tropical rainforests, and the
Antarctic. Tardigrades are among the most resilient animals known, with individual species able to survive extreme conditions – such as exposure to extreme temperatures, extreme
pressures (both high and low), air deprivation,
radiation,
dehydration, and
starvation – that would quickly kill most other known forms of
life. Tardigrades have survived exposure to
outer space. There are about 1,300 known species in the
phylum Tardigrada, a part of the superphylum
Ecdysozoa consisting of animals that grow by
ecdysis (shedding an
exoskeleton) such as
arthropods and
nematodes. The earliest known true members of the group are known from
Cretaceous (145 to 66 million years ago) amber, found in North America, but are essentially modern forms. Their origin is therefore likely much earlier, as they diverged from their closest relatives in the
Cambrian more than 500 million years ago.
Tardigrades are usually about 0.5 mm (0.020 in) long when fully grown. They are short and plump, with four pairs of legs, each ending in claws (usually four to eight) or suction disks. Tardigrades are prevalent in
mosses and
lichens and feed on plant cells, algae, and small invertebrates. When collected, they may be viewed under a low-power
microscope, making them accessible to students and amateur scientists. (Full article...)
Where common names are given, they are not necessarily the only common names in use for the species.