[Title fragment 1.1] [Title fragment 1.2] [Title fragment 1.3]
[Title fragment 2.1] [Title fragment 2.2] [Title fragment 2.3]
[Title fragment 3.1] [Title fragment 3.2] [Title fragment 3.3]

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"

[Auge in Auge mit dem Mönch]

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.
The image on the left is demonstrating the magic attraction of eye contact. Though the object measures only about 2 cm in height and though it is definitely not alive - just consisting of a few cubic centimeters of bronze - we feel attracted to it and very quickly we are forced into eye-contact with the unknown monk.

Last but not least our e-mail emoticons and 'smileys' prove that a few lines and dots are able to mimic a human face. In a similar manner we tend to superimpose our 'face feeling' on microscopic structures.
As amateurs in microscopy we are allowed to enjoy those strange feelings, whereas scientists have to be much more sober in order to protect their reputation of scientific objectivity.

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.
In any case it is worth while to have a look at those few reports in literature where microscopists describe their strange feelings at the moment when they came across their first water bear face under the microscope. Just have a look at the report by the Honourable Mrs. Ward, a 19th century microscope amateur who described her individual  'eye-contact feeling'  when stumbling upon her first water bear.

Strange enough, even scientists used an emotion-loaded vocabulary when writing about water bears: they are describing the tardigrades as strange, miraculous, even beautiful.   In order to have a look at some original quotations you might just go to the MICSCAPE article The incredible water bear   now.

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.
Body length ca. 250 µm.
Eyes of of focus: not visible at all.


Echiniscus water bear.
Focus on the eyes. The legs and claws are more or less out of focus.

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.

[tardigrades, Bärtierchen]

Microscopic view with rotifers, water bears, diatoms and a worm (nematode).

Engraving taken from Moritz Willkomms' book
"Die Wunder des Mikroskops"
[The Marvels of the Microscope]", (1856).

[tardigrades, Bärtierchen]

Detail of the previous figure.
Note the water bear 'face'.

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.

[tardigrades, Bärtierchen]

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:

[tardigrades, Bärtierchen]

Eye of a Macrobiotus tardigrade, as above, but in mixed raking light.
The red arrow is pointing towards the edge of a globular, transparent structure which might be interpreted as a lens.

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.

[tardigrades, eye lens]

Modern cross section through the head of an Echiniscus tardigrade (Proechiniscus hannae, top view).

Drawing on the basis of a scanning electron photomicrograph by Reinhardt M. Kristensen (see literature).

Grey: 'lens'
Red:  eye pigment spot

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.

[tardigrades, Bärtierchen]

Water bear Milnesium tardigradum. Still image from a video clip.
Both eye pigment spots are situated under glass-like spheroid structures. Overall, this looks very much like a working optical system.

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:

"Furthermore the eye has a uniform, strongly curved, distinctive lens."

Definitely a nice, old-fashioned understatement style ... just a few words with an extremely high information density.


Reinhardt M. Kristensen: Revision of the Echiniscidae. p. 271.
In: Roberto Bertolani (Ed.), Biology of Tardigrades. Modena 1987. p. 261 - 335.

Alexander Sokolowsky: Aus dem Seelenleben höherer Tiere. Leipzig 1910.

Moritz Willkomm: Die Wunder des Mikroskops. Leipzig 1856.

Raphael von Erlanger: Zur Morphologie und Embryologie eines Tardigraden ( Macrobiotus Macronyx). Vorläufige Mitteilung I. p. 584. Biologisches Zentralblatt 14 (1894) p. 582 - 585.

© 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.

Main Page