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As we have already learnt in the   April issue   the tardigrade is going to leave its old cuticula after moulting. Typically it uses an opening close to the head (or 'neck') of the old skin. Some authors think that the tardigrades use their stylets in order to pierce the old cuticula. But possibly the erratic movements before moulting alone are sufficient to tear the old cuticula and to free the tardigrade.


[ Ramazzottius oberhaeuseri with cuticula ]

Tiger pigmented tardigrade
Ramazzottius oberhaeuseri
shortly after leaving the old cuticula. Length ca. 350 µm.


The cuticula of this   Ramazzottius oberhaeuseri   has a net structure which is clearly visible:


[ Ramazzottius oberhaeuseri after moulting ]

Tardigrade Ramazzottius oberhaeuseri  directly after a moulting process.


Save the tardigrade now and put it back on a wet moss cushion by means of a fine glass pipette. Afterwards you will be able to study the details of the cuticula without bothering anybody living :-)
At medium and at high magnification the network type structure of the empty cuticula becomes even more obvious.


[ Cuticula of the tardigrade Ramazzottius oberhaeuseri ]

Fine structure of the cuticula of a
Ramazzottius oberhaeuseri
at moderate magnification.
The width of the small fields is about 2 - 3 µm.


[ Cuticula of Ramazzottius oberhaeuseri ]

Fine structure of the cuticula of a
Ramazzottius oberhaeuseri
at high magnification.
The width of the small fields is about 2 - 3 µm.


[ Cuticula of Ramazzottius oberhaeuseri ]

Fine structure of the cuticula of Ramazzottius oberhaeuseri. Top view of the cuticula of the hind body, seen at medium magnification.



[ Cuticula of  Ramazzottius oberhaeuseri ]

Fine structure of the cuticula of Ramazzottius oberhaeuseri.
Side view, similar to a real cross section. Perl-chain type structure.


When combining the results of our investigations from two different perspectives we come to the conclusion that the cuticula can be understood as a network of slightly lens-shaped elements, a craquelé, like smelting ice. With respect to the mechanical properties this structure will provide shelter and will be able to allow some movement as well though it will be not very flexible.


[ Cuticula of Ramazzottius oberhaeuseri ]

Hind part of a cuticula of Ramazzottius oberhaeuseri.


An empty cuticala can be easily overlooked at low magnification, in particular by beginners. You should try to enhance the contrast of the microscope illumination as much as possibly, even by means of closing the aperture iris. This will possibly spoil the optical resoultion of your fine microscope objectives but will certainly help you to spot the empty cuticulas. Try to touch and tear such an empty cuticula by means of fine needles. You will notice that it has a rather high tensile strength - just keep in mind that its thickness is in the range of one micron only! And you will find out that it is not elastic at all, which is trivy of course, as this is the reason why the tardigrades have to get rid of it.

The tardigrade has to perform a trick to leave this non-elastic cuticula: it has to diminish its body volume - one more property where the tardigrades perform superior to us humans!



Literature

There are many scientific publications dealing with the fine structure and permeability of the tardigrade cuticula and tardigrade epidermis.
In case you should have no electron microscopes beside your tv you might have a look at the following articles in order to get an impression what you might be able to see by means of expensive equipment and by complicated preparation work:

Greven, Hartmut: Die Bärtierchen. p. 15 - 20. Wittenberg 1980.

Greven, Hartmut und Greven, Wilma: Observations on the permeability of the tardigrade cuticle using lead as an ionic tracer. In: Bertolani, R. (Ed.): Biology of Tardigrades. p. 35 - 43. Modena 1987.

Kristensen, Reinhardt M.: On the fine structure of  Batillipes noerrevangi  Kristensen 1976.
I. Tegument and moulting cycle. Zoologischer Anzeiger 197 (1976) 129 - 150.


© 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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