Tardigrade

Tardigrade

A tardigrade

The tardigrade (Tardigrada), also known as the water bear or moss piglet, is a phylum of water-dwelling, eight-legged, segmented micro-animals. They were first discovered by the German zoologist Johann August Ephraim Goeze in 1773. The name "tardigrade" (which means "slow stepper") was given three years later by the Italian biologist Lazzaro Spallanzani.

Tardigrades are one of the most resilient animals known: they can survive extreme conditions that would be rapidly fatal to nearly all other known life forms. They can withstand temperature ranges from 1 K (−458 °F; −272 °C) (close to absolute zero) to about 420 K (300 °F; 150 °C), pressures about six times greater than those found in the deepest ocean trenches, ionizing radiation at doses hundreds of times higher than the lethal dose for a human, and the vacuum of outer space. They can go without food or water for more than 30 years, drying out to the point where they are 3% or less water, only to rehydrate, forage, and reproduce.

Classification

Tardigrades are classified as follows:

• Phylum: Tardigrada (Spallanzani, 1777)
• Class: Heterotardigrada (Marcus, 1927)
• Class: Eutardigrada (Bresslau, 1929)
• Class: Mesotardigrada (Thulin, 1928)

Anatomy and morphology

Tardigrades are usually about 0.5 mm (0.02 in) long when they are fully grown. They are short and plump with four pairs of legs, each ending in claws (usually four to eight) or sucking 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 very low-power microscope, making them accessible to students and amateur scientists.

Reproduction

Tardigrades reproduce either by laying eggs or through sexual reproduction. Males fertilize eggs that are then shed by the female or laid on a suitable surface, often the same substrate on which the tardigrades live.

Ecology and life history

Tardigrades are able to survive in extreme environments that would kill almost any other animal. Some can survive temperatures of close to absolute zero, or 0 Kelvin (−273.15 °C (−459.67 °F)), temperatures as high as 151 °C (304 °F), 1,000 times more radiation than other animals, and almost a decade without water. In September 2007, tardigrades were taken into low Earth orbit on the FOTON-M3 mission and for 10 days were exposed to the vacuum of space.

See also

• Cryptobiosis
• Extremophile
• Hypsibius dujardini
• Milnesium tardigradum
• Thermozodium esakii

External links

• Tardigrades – Information about tardigrades
• Tardigrada Register – A list of all known species of tardigrades

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