Report from the micro aquarium

Almost one year ago we have suggested a  new micro aquarium  which was based on an ingenious idea dating back to the 19th century. We had just translated Mr Varley's idea into a modern material.
By means of this micro aquarium we are now able to follow the normal life of the water bears for a longer period. The micro aquarium has a constant water volume and provides sufficient space and oxygen for the tardigrades.

Though some readers might consider it as old-fashioned, sentimental style: it is not much additional work to move the tardigrades back on a water-soaked moss cushion by means of a pipette after investigaton or when life conditions should degrade in the micro aquarium.
This behaviour is not only fair towards those tiny organisms that are much smaller than our own huge cell mass. Moreover you can prove the justification of the term "homo sapiens" just by showing a behaviour which is not driven by stupid aggression and destruction only.

Of course, the micro aquarium has its drawbacks, too: we have to be careful with continuous illumination, as the water might become too warm for the tardigrades (they like it cool). And we are forced to photograph through a rather thick water volume, by this reducing the image quality markedly. Last but not least the most interesting things tend to happen in our micro aquarium just at the moment when we are preparing a cup of coffee or when the telephone rings.

In order to watch the moulting and deposition of eggs we will have to spend some patience and energy. When moulting some tardigrades stop moving, even for days and nothing at all seems to happen. One might even think that the tardigrades are dead:

Water bear (heterotardigrade) at the beginning of the moulting process. Ventral view. The reduced size of the "new" animal and the intestine with its green content (plant juice) are clearly visible.
Body length ca. 0.3 mm.

When looking at the same place in our micro aquarium two days later we will notice that the water bear has left back its old skin, typically filled with some eggs:

Water bear skin with red eggs.
The water bear mother has left the scenery after having provided a safe place for the developing youngsters.

How did all this exactly happen? It would be fine if we were able to follow all the decisive steps of this process!

Obviously the water bear has to perform some hard work. Just keep in mind that the situation in the old skin is far from what we would call ergonomic - besides there is no food available during the moulting process.

Nota bene: this complex process seems to work without a consultant and it is definitely not ISO certified ;-)

We have been following the moulting in detail and are quite happy that we are able show the crucial moments here:

The beginning of the moulting process: the water bear shows no movements at all. In time lapse-photography it becomes obvious that the tardigrade doesn't much change its position within the old skin during hours.

Next morning: what is this? The green stomach content is placed cleanly besides the animal. It is hermetically closed like a garbage bag. By means of this trick the tardigrade has created a little bit more space within the cuticula.

About one hour later: a first egg has been deposited and is transported actively from the rear to the head region of the tardigrade.

15 minutes later: just on the right hand side of the first egg a second egg becomes visible (slightly out of focus).

After the deposition of the eggs the tardigrade has to leave the skin, usually with its backside first. This happens rather quickly, as can be seem from our miniature video clip:

After having dropped the garbage, after having completed moulting and after having deposited three eggs our tardigrade leaves its old skin, relaxing for a few seconds, like an astronaut in space.

© Text, images and video clips by  Martin Mach  (webmaster@baertierchen.de).
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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