The tardigrades or " bear cubs of water " form a junction (zoological) with whole share or " Phylum tardigrada". They are very close to the Arthropodes. The tardigrades were described (kleiner Wasserbär = small bear of water ) the first time by Johann August Ephraim Goeze (1731-1793) in 1773. The name " Tardigrade" mean “ slow Marcheur ” and was given by Lazzaro Spallanzani (1729-1799) in 1777.
The tardigrades are tiny animal multicellular, have a body segmented into four and protected by a Cuticule and are equipped with eight small finished legs each one by a claw (like small-scale models of bear with eight legs).
The tardigrades live a little everywhere on planet but are in greater number in the zones where one finds foam (like the Forêt S and the Toundra) because it constitutes, with the Lichen, their food of predilection. One finds of it top of the the Himalayas (with more than 6.000 m of Altitude), also in deep water (by 4.000 m basic) and in the polar regions or of the equator. They are also present in sand, the foams of the wet roofs, on saline Sédiments or of fresh water, where they can be very numerous (up to 25.000 by Liter).
Characteristics
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Their size : Largest (adults) can reach a length of 1,5 the millimetre, smallest below 0,1 millimetre. The coldly laid larvae can be smaller than 0,05 millimetre. The females can lay from 1 to 30 larvae at the same time.
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Their lifespan : It is of a few months only. However the tardigrades are able to return in Cryptobiose, which enables them to survive of very long periods without dying. the record of longevity is currently 8 years in a state of cryptobiose after which the tardigrades life income (Lauritz Sømme and Terje Meier 1995)
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Extreme resistance : The tardigrades have a very strong resistance to the Radiation S (X-rays) - more than 1100 times what the man can endure - and to the toxic products. The protection mechanisms (low detailed) their make it possible to survive under other extreme conditions like the absolute Vide, but also the high pressures or in an inhuman cold (several days with -272,8 °C, -458 °F) or with high heats (a few minutes with 150 °C, 302 °F).
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One their astonishing characteristics is their capacity with being frozen S for important lengths of time
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Details on the metabolic mechanisms which ensure their protection :
For that they retract their 8 legs in their body and dehydrate their organization almost completely (loss of more than 99% of their water), replacing water inside their cells by a Sucre which they synthesize. These sugars behave like a kind of Antigel and preserve the cellular structures. To supplement protection, they are rolled up in a small called microscopic wax ball small cask (form resembling a small barrel). At the time of the return to conditions known as " normales" , the bear cub of water or tardigrade, becomes again active in a few minutes or a few hours.
Classification
- 1000 species to date divided into three orders.
Internal bonds
External bonds
- Films and images of the tardigrade '' Hypsibius dujardini ''
- TARDIGRADA NEWSLETTER
- Another presentation of the tardigrade
- the tardigrade, a paradox of the evolution
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