In issue #36 we had started with our new topic 'tardigrade eyes'. First we had glanced at some statements taken from the scientific literature. But, apart from the obvious fact that those water bear eyes are very small, their anatomy and their capabilities remained unclear. |
"Water bears are looking at you" |
Direct eye contact is of utmost importance in
human communication. Fractions of seconds can be enough to visually exchange
emotions, to assess situations and to decide about necessary actions. |
Of course we tend to assume that the psyche of our microscopic water bears
must be more primitive than its human counterpart or e.g. the emotional
world of a cat. |
When seen at higher magnifications the water bear eyes appear as black (sometimes red) spots which we tend to interpret as eyes because of their position and bi-lateral symmetry. When taking photographs we will notice that it is impossible to represent a water bear from head to toe with all details being in focus. The most 'bear-like' portraits can be achieved when focusing on the lower half of the body with the eyes being completely unvisible because they are out of focus: |
Echiniscus water bear. |
Echiniscus water bear. |
When summarizing all this we simply note that the water bears seem to resemble 'higher' organisms also because they show us faces - whereas an amoeba or a rotifer seem to have no faces. |
Microscopic view with rotifers,
water bears, diatoms and a worm (nematode). |
Detail of the previous figure. |
When just looking at an isolated water bear 'eye pigment spot' at high magnification the visual impression and mental association with a face tends to vanish. |
Single eye-spot at high magnification. Transmitted light only. |
Most probably the discovery of the tardigrade eye lens has to be attributed to Raphael von Erlanger (1894). We have been working hard in order to show the structure which Raphael von Erlanger might have seen more than 100 years ago: |
Eye of a Macrobiotus tardigrade,
as above, but in mixed raking light. |
Modern scanning electron photomicrographs by the Danish scientist professor Kristensen provide further evidence that there might be some kind of eye lens in tardigrade anatomy. |
Modern cross section
through the head of an Echiniscus tardigrade (Proechiniscus hannae, top view). |
Further light microscopic investigations on Eutardigrade water bears provided similar results: Many species do have transparent structures with lens-like geometry above the eye pigment spots. |
Water bear Milnesium tardigradum.
Still image from a video clip. |
Now we will
hand over the virtual microphone to Professor Raphael von Erlanger, quoting him
with his own, very short report of his water bear eye lens discovery:
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LiteratureReinhardt M. Kristensen: Revision of the Echiniscidae. p. 271.
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© Text, images and video clips by
Martin Mach (webmaster@baertierchen.de).
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