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We have promised to present a micro aquarium for water bears here, following Varley's principle of the capillary cage. In the beginning we have experimented with ordinary cover glasses and small glass plates cut by means of a diamond glass cutter to be joined by epoxy resin glue. But this pathway turned out as a catastrophy and was finally dismissed.

Our next idea was to have a look at typical everyday products in storehouses. In the end we came to the conclusion that all those products never have really flat and optically clear bottoms and that they tend to have dimensions far from the design necessary for a capillary cage. And this is fully understandable as a pound of shugar does need more space than a few water bears and as probably nobody will really want to study the pound of shugar in its box by means of a microscope ;-).
But in the end we have found a solution which is surprisingly simple and cheap. We will pass it on to our readers:


[ the new micro aquarium ]

The revolutionary micro aquarium, as seen from above. It is a modern version of Varley's 'capillary cage' micro aquarium.

Left: empty.
Right: filled with water.


The specifications are as follows: basically, it is made out of a transparent, artificial resin. It has the shape of a very flat cylinder.

Maximum overall diameter: 39 mm
Inner (usable) diameter: 33 mm
Height, overall: 5.6 mm
Usable interior height: 3.6 mm
Thickness of bottom and cover: 1 mm each

The thickness of the bottom (1 mm) is the same as the thickness of a slide, so our substage system (condenser) will work as usual. The micro aquarium can be used in two ways:


[ micro aquarium; cross section ]

Micro aquarium, used as a classical capillary cage. Note the water column in the middle which is trapped within the cage but has in fact no contact with the side walls.

a) Regular use: a little bit of water with the water bears is being transferred to the center of the lower part of the aquarium by means of a pipette. You will notice that the water does not tend to creep to the outer edges like with glass but instead will remain as a clean spheroid droplet in the middle. When closing the box the droplet should come in contact with the cover and bridge to the cover.


[ micro aquarium, cross section ]

Use for higher magnifications. Note the tiny droplet in the center of the lower part of the aquarium, covered by an ordinary cover glass. Small pieces of cover glass serve as distance keepers in order to guarantee a safe height for the water bears.

b) Use as a sub-micro aquarium for higher magnifiactions: A very small droplet of water is being transferred to the lower part. Tiny cover glass pieces serve als distance keepers. A normal cover glass can be used. After investigation the micro aquarium can be closed with its cover in order to prevent desiccation.
Those among you who are lucky to own a water immersion objective can of course directly dip into the water droplet with their objective and therefore will not need a cover glass at all, even for higher magnifications.


The micro aquarium provides enough space to see the water bears from unusual perspectives. We have made a few photographs:


[ tardigrada tardigrade tardigrades ]

Tardigrade, sitting on a small soil particle. As seen from behind.
Dark field illumination.
Note the tiny claw on the left side. Width of the animal ca. 100 µm

[Due to the enormous depth of 3 mm the image quality will deteriorate a little bit but we think that the perspective makes up for this drawback].


[ tatdigrada tardigrade tardigrades  ]

Tardigrade, crawling. A nice 3D perspective as well. Incident light [reduced image quality due to high water depth].


Our micro aquarium will function with most objectives up to an objective magnification of 10. Don't be afraid that you will have to spend your last US$ 100 bill for this project. The costs for a single micro aquarium are less than 1% of this sum but probably you will have to buy packages with 10 pieces ...

Here is the  solution  !


Are you still looking for a christmas tardigrade gift?

Be wise and don't ask at your local grocery for this.
Suggestion #1: a tardigrade clip on floppy disk, just for discussion and for the fun of it.

With most web browsers it will be sufficient to right-click on the video with your mouse and then select a download/copy option in order to copy the clip onto a floppy disc.
Please accept that we will give no technical advice for this goodie. And please write the congratulation text yourself ...

  tardigrade video clip (only 220 k in size)


Suggestion #2: a tardigrade logo for the mobile.

[ Tardigrade Handy Logo Vorlage]

It is up to you to fit this and send this to your mobile. Here is the pattern only.


© 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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