In  issue #18  we had discussed  zoological systematics   in general and we had touched water bear species determination, too.
We are now aware of the fact that the various water bear species may be difficult to discern. Sometimes it would be even necessary to kill a water bear just in order to find out its scientific name ... so it is certainly more appropriate for us amateurs to enjoy the water bears anonymously but alive.
We had also discussed an eutardigrade egg, presumably of the water bear   Macrobiotus areolatus  which had a complicated, delicate outer geometry and therefore kept its inner structure secret from us.
This time we will look at a heterotardigrade (echiniscus) water bear egg with smooth surface. Due to its small dimensions it is fully transparent:

Water bear (echiniscus) egg,
Ø ca. 40 µm.
In the center the mouth tube with its root-type endings, left and right of it the two straight stylets. The animal is fully developped and ready for hatching. The legs and claws cannot be seen here as they are on the other side of the egg.

There is no or little visual difference between the eggs of the various species within the  genus echiniscus . As a consequence the eggs are not helpful for echiniscus water bear species determination, instead we have to look at the grown-up individuals. Some of them really resemble jelly bears, in particular when seen in incident light:

Echiniscus tardigrade,
in mixed light
(previously published in the magazine Creation, Brisbane, Australia,
© Martin Mach 11/2001).

It is not possible to get a crisp light microscopic photograph representing all the filaments and thorns of those echiniscus water bears. In this case classical drawings are much superior. Below we have reprinted a fine historical illustration from a biology textbook showing an echiniscus water bear:

"Echiniscus creplini".
Illustration from: Ludwig K. Schmarda, Zoologie. Vol II., p. 58. Vienna 1878.

Note the details: Spherical pharynx with thin mouth tube (signalizing a vegeterian habit); two long, thin straight stylets for piercing plant cells; thorns at the first pair of legs; tiny reinforced bases of filaments; fine structure on armour plates; eye spots present.

On the other hand modern media might be more appropriate to show how the armour plates work together as a highly flexible system:

Video clip: flexible armour of an Echiniscus back.
Note that the thorns and filaments are almost invisible in this representation. Legs, claws, nose and eyes are out of focus.

Many details of the armour plates cannot be studied when looking at living animals. But sometimes you will find empty skins, remains of the moulting process. These can be studied in detail without doing any harm to a water bear. In any case you will need a high quality microscope for the investigation of those tiny details. Some structures can be seen only by means of oil immersion objectives:

Detail of the back of an echiniscus water bear: delicate framework of armour plate, thorn.

Detail of the back of an echiniscus water bear: armour plate with filament ('hair').

Echiniscus water bear armour plates.
As the water bears have no lungs and no circulation system the outer oxygen must find its way by diffusion through the joints between and the pores within the armour plates.

And now we will explain, though in a simplified way, one criterion for echiniscus water bear species determination. Fig. 1 shows the back of one of the parents of the egg represented at the beginning of this article, as seen in the light microscope. Fig. 2 is an explanation of what can be seen when looking at all the various focus levels:

fig. 1: back of an echiniscus water bear, photomicrograph

fig. 2: back of an echiniscus water bear, nomenclature

Explanations: the roman numbers in fig. 2, left side, refer to the body plates I to IV.
K is the head plate, body plate I is sometimes called shoulder plate.
The red inscriptions S1 to S3 indicate the positions of the so-called intermediate plates which are closer to the body than the more massive body plates.
The capital letters A to E indicate the positions where filaments can be situated. In the example shown here filaments are present in positions A and C, they are lacking in positions B and D.
The filaments on level C are oriented in two different manners, laterally and dorsally, another position might be in-between (dorso-lateral). Furthermore we notice dorsal thorns in position D.

According to MARCUS (see literature) many echiniscus species differ in type and position of filaments and thorns. As an example, once again following Marcus, we have prepared a table with increasing 'hairyness' of some closely related echiniscus species:

Furthermore all water bears of the Echiniscus blumi series have two lateral filaments in position A. So, following MARCUS, our tardigrade from fig. 1 would have to be determined as  Echiniscus mediantus .

Sworn to strict secrecy the editors of the Water Bear web base have been working on a new project: we have introduced a new synthetic substrate which might be more appropriate than natural moss to study the  cryptobiosis   of the water bears. The results will be presented in the next issue.

Come in next month, please.

Literature

Ernst Marcus: Tardgrada. p.125. Berlin 1936.

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© 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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