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Maritime tardigrades (VII) - anatomical detail of Batillipes

We do receive many e-mails my microscope amateurs, some of them asking for a detailed printed tardigrade species determination algorithm. Of course, this algorithm should reach down until well below species level, if possible even into all species variations. It should be fairly easy to use and to understand and it should be valid for all tardigrade individuals worldwide - at low cost, in English, not in one of those old-fashioned European languages. But we are terribly sorry to state that this determination key doesn't exist at the moment.

Apparently the grandseigneur of tardigrade species determination, Italian scientist Giuseppe Ramazzotti, in co-operation with Walter Maucci, was the last to try. His impressive monograph entitled "Il Phylum Tardigrada" (3rd edition, 1983), is written in Italian language and comprises more than 1,000 pages. Unfortunately it is out of print and it is expensive when bought from an antiquarian. Some of the more lucky people own an authorized English translation CD by Clark Beasley.

On the other hand the Ramazzotti bible is > 25 years old. As a consequence you will not find newly detected species therein, like e.g. a bizarre tardigrade marvel called Tanarctus bubulubus with "buoyant" bodies as Prof. Kristensen from Denmark describes it. And you will not find the funny Milnesium tardigradum-relative Milnesioides exsertum with its extra-long nose, as discovered by tardiologist Sandra K. Claxton in remote Tasman regions.

Though a new, universal tardigrade species identification textbook is missing, there are many exquisite "genus reviews" (i.e. partial tardigrade taxonomy chapters) to be found in the more recent literature, in particular within the various tardigrade symposium proceedings. But be warned: some of those more special publications are terribly expensive. Moreover, even with most of the modern literature at hand, some species determinations, in particular those of exotic tardigrades from remote, touristic locations might still remain doubtful.
In contrast to the scientific world the amateur can escape to a less serious style of investigations, simply concentrating on deliberately chosen details. As an example we would like to mention a study of the Batillipes median cirrus. This median cirrus has been interpreted by Ernst Marcus as a kind of water level sensor, with the tardigrades escaping downwards when sensing low tide. Besides, we have no idea about the exact function of the "worm" which sometimes can be found on the tip of the median cirrus:

[ Median cirrus odf a Batillipes tardigrade ]

Median cirrus (arrow) at the front end of the Batillipes sp. body.
Please note the typical punctuate pattern on the cuticula as well.
Image width ca. 30 µm.

Two structures on the head of Batillipes resemble eyes. But according to the scientific literature they shouldn't be interpreted as eyes. This would imply that our most agile Batillipes tardigrade is moving through its hard edge sand grain world without any optical control! But we can't help it, as there appear to be no nerves endings in those eye-spot like structures.

[ eye spot like structures of Batillipes ]

Head of Batillipes with two "non-eye" spots.

Though not a taxonomic criterion, the nerve and muscle system of Batillipes is quite impressive. We have already seen in the last issue that Batillipes appears to be a highly sensitive, even nervous animal, with the ability to move backwards (most other tardigrades are not able to behave in this manner).

[ nerves and muscles of a Batillipes tardigrade ]

Perfectly wired: nerves and muscles of a Batillipes sp. tardigrade.
Image width ca. 200 µm.

The existence of a tail and its morphology are considered to be important taxonomic criteria, though there appears to exist an intra-species variability as well: some individuals within a given tardigrade population apparently have simply missing tails. So, the non-existence of a tail might be misleading. But, on the other hand, the existence of a given tail morphology is a quite useful taxonomic property. Sometimes the tail might just be a small lump as shown in the image below. Besides, we were not able to find this particular tail form in the scientific literature.

[ Batillipes hind side ]

Hind side of a Batillipes sp. tardigrade from the French Atlantic Coast.
Image width ca. 100 µm.

In some cases the tail might be lengthy but very thin. As a consequence it might be difficult to distinguish whether it is actually some kind of tail or just a little bit of detritus adhering to the back of the tardigrade body:

[ Batillipes tail ]

Fine tail protrusion of a Batillipes sp. male.
Image width ca. 300 µm.

The hopeful amateur might end up in a similar manner as the professional tardiologist, measuring all leg and toe lengths, counting spurs and filaments, most of which are perfectly modest structures hidden along the legs or the backside of the mysterious tardigrades. Our advice is to leave the specialities to the specialists. But, in case you should casually delve down into those depths, don't forget that tardigrade studies are thrilling and beautiful adventures and that they should stay like that ...


S. K. Claxton: Milnesioides exsertum gen. n. sp. n., a New Tardigrade from Australia (Tardigrada, Milnesiidae). Contribution to the 7th Symposium on tardigrades, held at Düsseldorf, Germany, in September 1997. Zoologischer Anzeiger 238 (1999) p. 183 -190.

A. Jørgensen und R.M. Kristensen: A new tanarctic arthrotardigrade with buoyant bodies. Zoologischer Anzeiger 240 (2001) p. 425 - 439.

E. Marcus: Zur Anatomie und Ökologie mariner Tardigraden.
Zool. Jahrb. 53 (1927) p. 487 - 588.

W. Maucci: Tardigrada. Vol. 24 within the series "Fauna d'Italia". 388 pages. Bologna 1986.

G. Ramazzotti, W. Maucci: Il phylum Tardigrada (3rd edition).
Memorie dell' Istituto Italiano di Idrobiologia 41 (1983) p. 1 - 1012.

© 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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