Indirect tardigrade microscopy (the study of the cuticulae)

The tardgrade cuticulae, kind of transparent skins, are left back by the water bears after a moulting process. As we do really like the tardigrades we want to point out once more that the microscopic study of a cuticula doesn't cause any harm to the tardigrade and still can be performed at very low working distance and extremely high magnification, e.g. by means of an oil immersion objective.

But one obvious obstacle in this endeavour is to find a cuticula at all. Sometimes you will notice them when slighty stirring the water in the petri dish, as they behave in a slightly floating manner, like any object of low specific density. An other possibility is to look out for individuums in the moulting process - typically with a slightly contracted intestine and temporarily lying still. After some time (up to two days) they will finally climb out ouf their cuticula which can then be recovered by means of a pasteur pipette.

The photomicrograph below is illustrating a typical early stage of the moulting process of a marine tardigrade. It becomes clear that the legs of Halechiniscus are rather long, stretching out like telescopes. This mechanism comes in handy when the tardigrade is still standing on its home sand grain and stretching out for the next (target) sand grain.

Halechiniscus sp. tardigrade from Craotia, in the starting phase of the moulting process.
Image width ca. 0.3 mm.

In the next photograph the head is already partially detached from the outer cuticula. As a consequence the overall transparency is enhanced and we are able to see further detail like a nerve line extending to the sensory protrusions in the head region.

Halechiniscus sp. tardigrade, during moulting.

Finally the tardigrade will succeed and hopefully get rid ot its loose outer 'skin'. It should be kept in mind that the moulting process is highly risky for the tardigrade as it cannot feed in this time and as it is restricted in its movements and reactions towards the outer world.

One advantage of the moulting process is that the tardigrade is getting rid of all marine residues and tiny parasitic organisms clinging to its skin.

Cuticula of a Halechiniscus sp. tardigrade from Croatia, left back after moulting, with lots of incrustations. Image width ca. 0.3 mm.

Our microscopic advantage is that further anatomic detail becomes visible as the empty cuticula is an ideal microscopic object: flat like a pancake and highly transparent. So wie are e.g. able to recognize some kind of 'navel' (which is - of course - not a navel, just something different ...).

© 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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