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Tardigrade hide-and-seek

From time to time we do receive very kind and flattering e-mails, praising our easy-going, entertaining text presentations. Thank you! But nevertheless we are quite aware of the restrictions which are a consequence of this shorthand style, in a mixture with irony and lack of scientific seriousness. Just keep in mind that the famous 20th century tardiologist Ernst Marcus condensed his understanding of tardigrade cryptobiosis in 12 (!) full pages. As a consequence our intellectual level cannot be quite at par with those splendid publications. Our only advantage being that Ernst Marcus was slightly wrong in so far as he thought that tardigrades weren't photographable at all. That's the reason why all his publications are illustrated by (excellent) drawings only.

Those among you who want more precise information should try to get their hands on the more serious scientific literature. And in particular the books by Ernst Marcus still can be recommended to everyone who is able to read in German language. It is a pity that they have not been translated to English yet. Much of the wisdom packed in those hundreds of densely filled pages is in danger to run into oblivion due to the language barrier. Besides Erst Marcus sometimes is serving as a kind of rubstone for younger scientists who try to critizise him - being well aware of the fact that he cannot hold up against the attacks any more. So you might get some insights to scientists' psychology when reading Ernst Marcus' books and comparing the contents to what is written about Ernst Marcus. In any case it is quite a pleasure to follow his splendid discussion of cryptobiosis, e.g. his line of thought why cryptobiosis is not triggered by drought but instead by a lack of oxygen (see literature, as cited below, pages 178 to 190).

In contrast to Ernst Marcus' time we can make lots of photomicrographs without caring about film and development costs. Given time we can collect thousands of tardigrade photographs just by pressing the remote control of our digital microscope camera. As a consequence it is becoming increasingly difficult to keep track of the photographs and their content. But from time to time we are scrolling back through our photographs and do note something that has not been shown in this magazine yet.

The first photograph of this type as shown below is depicting an eutardigrade water bear, a few minutes after revival from the dry state, still hiding deeply in a cavity of the moss jungle. It is well known that the tardigrades are using the moss plant walls in a similar way as humans are using blankets. Presumably this has not only the advantage of a more agreable and relaxed desiccation process but it will as well serve as a protection against raptor enemies in the "other" world, the dry world: whereas the tardigrade cannot move and defend itself in the dry state, many other organisms are quite active in this dry state world, thus might consider to devour dry state tardigrades (like potato chips!).

The habitus of the revived tardigrades looks a little bit like a scenery from "Jurassic Park", doesn't it? But agreed, the tardigrades are definitely a little bit smaller.

[ Eutardigrade behind moss leaf, transmitted light ]

Eutardigrade, after addition of water to moss, still hiding behind a moss plant wall.

When screening dry moss samples we often underestimate the population numbers as most of the tardigrades will hide behind the curled moss leaves, with some tardigrades being fully covered by the plant cells. But with some patience and appropriate illumination we can spot the tardigrades behind the dry moss plant walls as well.

[ Echiniscus sp. tardigrade behind moss leaf, incident light ]

Red Echiniscus sp. tardigrade in the dry state, perfercly hidden behind a moss leaf. The tardigrade "tun" is about 1/20 mm in length. Transmitted light, with the stomach-intestine region visible. The ripples are caused by the cell structure of the moss.

The same scenario looks quite different when seen in transmitted light:

[ Echiniscus sp. tardigrade behind moss leaf, transmitted light ]

Red Echiniscus sp. tardigrade in the dry state, perfectly tarnished behind a moss leaf. View as above but seen in transmitted light, with the body color appearing in a more vivid orange.

How do you think a tardigrade might feel when being overcome by cryptobiosis? Does it feel like some dizzyness after an alcoholic beverage, or simply like quite normal human tiredness? Or does it resemble a more dramatic scenario, e.g. like a heart attack? Or does it resemble a kind of partial death?

But perhaps we are once more overrating the tardigrade brain and nervous system? Is a tardigrade able to be afraid of the things to come or is it simply going to sleep, not caring about the future at all?

In any case the tardigrade is making use of the minutes before cryptobiosis, trying to hide in natural cavities for a relaxed cryptobiosis (drying) adventure. And, as all our readers know there is definitely some hope for revival after desiccation. So, do we have an animal that is repeatedly entering heaven and then returning to life? With a multiple heaven's flashback experience?


Ernst Marcus: Tardigrada. Leipzig 1929. 608 pages (please note that there is a similar, much smaller monograph by Ernst Marcus, too!).

© Text, images and video clips by  Martin Mach  (webmaster@baertierchen.de).
The Water Bear web base is a licensed and revised version of the German language monthly magazine  Bärtierchen-Journal . Style and grammar amendments by native speakers are warmly welcomed.

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