"Size matters!" - in search for the Locus typicus of Batillipes mirus (III)

As already reported in the previous issue we had been unable to find any maritime tardigrade in the Kiel Foehrde at first. Even though we had brought along a small dissecting microscope for sand material sample screening, none of the Batillipes  giants  as documented in literature by Prof. E. Marcus (720 µm!) came into view.

But, as every microscope amateur knows, there are huge differences between fashionable and fierce field microscope in-situ work and domestic desktop microscopy. At home the environment is more quiet and the ambient light situation can be perfectyl adapted. The desktop microscope is heavier, its controls run smoother and as a consequence it is balsam for the nerves of those who are hunting nervous maritime tardigrades. Even though some of you might achieve similar results when sitting outside on a wind shaken rock edge with the pocket microscope in hand, home based microscopy will be much more relaxed. No matter which pathway you should prefer, the decisive question behind all this is: to find or not to find?

In any case, back home we were able to find a single tardigrade after some hours of sand-screening. Furthers were to follow.

Batillipes tardigrade from sand sample #2 as described in our previous issue (from Kiel Foehrde, near Strande), climbing on a sand grain. Body length ca. 0.2 mm.

Its colleagues were perfectly able to hide behind the sand grains, furthermore keeping still at the slightest distress.

Batillipes tardigrade from sand sample #2 (Kiel Foehrde, near Strande). Fully grown up female, ovary appearing grey, stomach-intestine brown with lobed contour. Body length ca. 0.2 mm.

In the very beginning of our studies we thought that all those individuals might be juveniles or simply belong to another Batillipes species, not Batillipes mirus. But, already at moderate magnification the characteristic caudal appendix spine of Batillipes mirus became visible (see images below).

Batillipes mirus, on sand grain, in incident light.
The white spot in the hind body is a mature egg. Body length close to 0.2 mm.

Further body length measurements revealed that "our" Batillipes mirus tardigrades had a typical body size of 0.2 mm, much less than those 720 µm reported in literature. So we finally understood why we had not been successful during our first in-situ search. We had simply been expecting something markedly bigger.

Batillipes mirus,
on sand grain, with 1/100 mm scale overlay. In this case the invidual shown measures about 130 µm in length, when stretching 150 µm at most.

When seen under the desktop microscope at higher magnification the slightly conical geometry of the appendix becomes clearly perceptible, even though the "in-sand" photomicrography technique will always remain a challenge.

Hind body of Batillipes mirus with the characteristic appendix.

As most of our readers will already know, we do not appreciate blind formaldehyde killing with subsequent microscopic inspection. But, as we are located a few hundred miles from the next ocean, the question is: how to care for live maritime tardies at home, if possible in a micro aquarium? Funny enough, it turned out to be perfectly simple.

The rather modest micro aquarium as shown below was well able to keep the maritime tardigrades alive and reproducing for more than six months! It consists of a transparent plastic container, measuring ca. 14 cm x 7 cm x 7 cm. It is not tremendously expensive as it is in fact an empty "Ferrero Rocher®" praliné box.

One major trick is to use it uside down. Only a thin layer of sand and shallow water is needed. Thus we can still perform direct microscopical observation in the micro aquarium. The formerly lower part of the praliné container now serves as a cover. Its only role is to impede evaporation thus keeping the salt content of the water approximately constant. It is of vital importance to keep the aquarium in full shadow and moderate light, e.g. on a window sill oriented to the north. You should prefer cool temperatures, but temporary heat periods with up to 25°C will be tolerated by most of the maritime tardigrades. The subdued light will cause a slow growth of algae, providing sufficient nutrition for your tardigrades and at the same time helping to avoid uncontrolled algae growth and poisonous decomposition products. Very simple, isn't it?

Live ocean life, even on the countryside - perfect :-)

The "Rocharium", a special micro aquarium for maritime tardigrades, being in fact a "Ferrero Rocher®" praliné box. No electricity needed, no pumps, no filtering necessary. Just be careful to fill in rather clean sand samples, without any bigger organisms, algae etc. Overall, a very simple and very efficient budget sea water aquarium, well suited for anybody who owns a microscope - and fascinating. Keep cool, strictly avoid sunlight and, above all - do not feed, it is all in!

Literature

Ernst Marcus: Zur Anatomie und Ökologie mariner Tardigraden. Zoologische Jahrbücher, Systematik, vol. 53 (1927) p. 487 - 558.
[Comment: we think that this is the ultimate source about Batillipes and Echiniscoides, even though it is written in German and ca. 80 years old. Ernst Marcus, expelled from Berlin by the Nazi Government in the 1930s, was the most prominent and most ingenious tardiologist of the 20th century. Most of his illustration material is deliberately copied up to the present day and used for all kind of modern tardigrade publication illustrations.]

Ferdinand Richters: Tardigraden-Studien.
In: 40. Bericht der Senckenbergischen Naturforschenden Gesellschaft.
Part II: Wissenschaftliche Mitteilungen. p. 28 - 48 and 2 tables. Frankfurt am Main 1909.
[Comment: contains the first (!) photomicrography of a Batillipes tardigrade]

© Text, images and video clips by  Martin Mach  (webmaster@baertierchen.de).
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