Tardigrades: drawing vs. photomicrograph

When we began with this internet magazine, ca. 20 years ago, our aim was to make clear that there is a widely unknown microscopic world beneath our daily awareness - kind of a parallel world.

And now, a lot later, we still feel excited when we come across our tiny friends under the microscope.

Fig. 1: an Echiniscus tardigrade inhabitant of planet Earth - like you and some others ...
This one came from the roof of a Munich bin shed. The photograph is documenting a view through a stereo (dissecting) microscope on a wetted moss sample in a petri dish.
The field of view is 4.3 mm in width, the size of the orange tardigrade approximately 0.3 mm. Thus the tardigrade might be perceived as a tiny spot by means of the bare eye. But of course you will actually never see one when going for a walk without your microscope.

Even though we tried to optimize our photomicrographic technique over the years we must still concede that the actual visual impression through a binocular microscope appears much clearer and more lively than one of our photographs. And, though some among you might not believe it, there is still a problem of credibility: many people, some even with an academic background, are thinking that our photomicrographs and videos might be merely products of phantasy and digital imaging!

Early 19th century tardiologists had to overcome even more problems - not only with respect to credibility but with respect to - hopefully - crisp photomicrographic focusing. And there was the terrible low light performance of the film material. As a consequence, photography through a microscope formerly was an extremely tedious task. One had to resort to dead or asphyktic tardigrades in order to avoid motion blur. The most famous tardiologists at this time thought that the tardigrades were simply "unphotographable" and therefore clearly emphasized drawings.

Let's explain and have a look at a drawing of Echiniscus gladiator made by the Scottish biologist James Murray (fig. 2). We do like it. When looking closer one might think about a caricature or a funny joke, possibly referring to a political election in the United States.

Fig. 2: the tardigrade Echiniscus gladiator, as probably drawn by its discoverer, James Murray. One might think about it as a funny joke - but it probably wasn't meant to be one.

In both, drawing and photomicrography, there is the problem of three-dimensionality: when drawing at the microscope the image is uninevitably looking flat, not three-dimensional. The reason behind this is the terribly low depth of field in classical light microscopy. It forces the operator to position the tardigrade in a rather flat volume, a kind of a horizontal sharpness slice. In the worst-case (and possibly quite normal) scenario the tardigrade is strongly compressed between the microscopic slide and the microscopic cover glass. As a consequence the operator tends to copy an unnatural flat visual impression into a flat drawing, though - of course - in reality a tardigrade is a very three-dimensional animal. Even worse, the flattened tardigrade appears to have 4 instead of 8 legs in those flat-world representations (see fig. 2 and fig. 3).

Fig. 3: a drawing of the tardigrade Echiniscus quadrispinosus, a species discovered by Ferdinand Richters.

So the restrictions of a 1:1 transfer from the flat microscopic view are perfectly clear. Instead of harvesting the full advantage of a classical drawing most "scientific" tardigrade images are flat world images - which is a pity. One can demonstrate the effects nad shortcomings of the transfer as follows: once you are using a tardigrade photomicrograph and convert it to b&w it does exactly look like one of those early scientific drawings. Of course much more skill and imagination are requested in order to produce a tardigrade portrait in its full three-dimensionality. Funny enough, the three-dimensional representations appear to have been despised by the more serious tardiologists. As a consequence the so-called "habitus" drawings (truly three-dimensional drawings) are extremely rare in the scientific literature.

Fig. 4: The 'bin shed' tardigrade, photographed in the so-called asphyctic (unconscious) state. The animal shown here is slightly smaller than the one shown in fig. 1, measuring ca. 0.2 mm in length. Please note the different (true) orientation of the claws. In this old-style photomicrograph only four of the eight legs are invisible, like in the drawing, hiding behind their counterparts.

Fig. 5: Same as fig. 4 but converted to b&w by digital imaging. Definitely "old style but still in deep appreciation for both James Murray and Ferdinand Richters!

In any case it becomes clear that our ancestors mostly made use of non-moving, flattened tardigrades for documentation, with the tardigrades being heavily compressed, dead or in the asphyctic state. Only very few illustrators found their way to more realistic, three-dimensional tardigrade portraits like those published by Ernst Marcus ca. 100 years ago:

Fig. 6: Truly three-dimensional tardigrade artwork drawing (a so-called "habitus" image)
as published by Ernst Marcus in 1927

Image sources

Fig. 2, fig. 3 and fig. 6 are copies from Ernst Marcus' splendid monograph: Bärtierchen (Tardigrada). Jena 1928.
It is assumed that fig. 2 therein is based on even earlier work by the Scottish scientist James Murray and fig. 3 on a sketch by the German biologist Ernst Richters.

© 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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