Tardigrades – The Water Bears

Posted on 26 September 2009 Crni

Tardigrades (commonly known as water bears) form the phylum Tardigrada, part of the superphylum Ecdysozoa. They are microscopic, water-dwelling, segmented animals with eight legs. Tardigrades were first described by Johann August Ephraim Goeze in 1773. The name Tardigrada means “slow walker” and was given by Spallanzani in 1777. The name water bear comes from the way they walk, reminiscent of a bear’s. The biggest adults may reach a body length of 1.5 mm, the smallest below 0.1 mm. Freshly hatched larvae may be smaller than 0.05 mm. More than 1000 species of tardigrades have been described. Tardigrades occur over the entire world, from the high Himalayas (above 6,000 m), to the deep sea (below 4,000 m) and from the polar regions to the equator.The most convenient place to find tardigrades is on lichens and mosses. Other environments are dunes, beaches, soil and marine or freshwater sediments, where they may occur quite frequently (up to 25,000 animals per litre). Tardigrades often can be found by soaking a piece of moss in spring water.

tardigrade water bear

Tardigrades are polyextremophiles and are able to survive in extreme environments that would kill almost any other animal. Some can survive temperatures close to absolute zero, temperatures as high as 151 °C (303 °F), 1,000 times more radiation than other animals such as humans, nearly a decade without water, and even the vacuum of space.

tardigrade

Tardigrades are polyextremophiles and are able to survive in extreme environments that would kill almost any other animal. Some can survive temperatures close to absolute zero, temperatures as high as 151 °C (303 °F), 1,000 times more radiation than other animals such as humans, nearly a decade without water, and even the vacuum of space. Tardigrades have a body with four segments (not counting the head), four pairs of legs without joints, and feet with claws or toes. The cuticle contains chitin and is moulted. They have a ventral nervous system with one ganglion per segment, and a multilobed brain. Their pigment-cup eyes are rhabdomeric. Instead of a coelom they have a haemocoel. The only place where a true coelom can be found is around the gonad (coelomic pouch). The pharynx is of a triradiate, muscular, sucking kind, armed with stylets.

Although some species are parthenogenetic, males and females are usually present, each with a single gonad. Tardigrades are eutelic (all adult tardigrades of the same species are believed to have the same number of cells) and oviparous. Some tardigrade species have as many as about 40,000 cells in each adult’s body, others have far fewer

3 Comments For This Post

  1. Ormewood Says:

    I can believe that it can survive at zero degrees Celsius or zero degrees Fahrenheit, but not at temperatures near absolute zero.

    Temperatures approaching absolute zero have only been achieved in a few experiments. None that I know of have involved living organisms.

  2. Tardigrade Says:

    @Ormewood: Well, almost at least (from Wikipedia): “Some can survive temperatures of -273°C (-460 °F), close to absolute zero,[5] temperatures as high as 151 °C (303 °F), 1,000 times more radiation than other animals,[6] and almost a decade without water.”

    The reason is that all water is replaced by sugar (that doesn’t expand or contract) when facing such extreme conditions.

    Apart from the tardigrades’ ability to survive the harshest of situations (at least in a dormant state), biological analogues are very interesting, and it just so happens that symmetrical multiple ‘limbs’ are very good for holding on to things and to stabilize one’s movement and posture. Also, ‘claws’ are very good for getting traction. And that works for real bears too, despite the fact that bears can be more than 1000 times bigger than tardigrades.

    Here are two great sites about tardigrades, with lots of pictures:
    http://www.baertierchen.de/main_engl.html
    http://tardigrades.bio.unc.edu/

    And yes, Tardigrade is the pseudonym I use the most when commenting on stuff, so don’t copy it.

  3. CryoBoy Says:

    Better believe it — Most organisms can be cryopreserved and brought back to life with a very high success rate. The trick is to eliminate water which expands when frozen causing cell membranes to break. Anhydrobiotic (cryptobiotic) organisms including the Tardigrade (water bear), some nematodes (worms), plants, algae, fungi, bacteria routinely use this strategy of “suspended animation” by the elimination of water as part of their life cycle. How long life can last at temperatures approaching zero degrees Kelvin (absolute zero) is unknown. At liquid Nitrogen temperatures even human embryos and tissue culture cells are stored for many years. PS That article had the best “Water Bear” picture (SEM) I’ve ever seen !

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