Thai tardies (III) - Batillipes taxonomy

From time to time microscopy amateurs are discussing tardigrade taxonomy and tardigrade taxonomy literature within internet forum threads. Most dialogues will end up with a hint towards the German language monograph by Hartmut Greven (1980) or the more expensive book by Ian M. Kinchin (1994). Both of these are nice books but the authors definitely do not intend to present a tardigrade determination down to species level.

And it is interesting to note that the last comprehensive taxonomy book of the Phylum Tardigrada by Guiseppe Ramazzotti and Walter Maucci (3rd edition: 1983, more than 1,000 pages) appears to be almost unknown to a broader audience, possibly because it is rare and because it is written in Italian language.

As a consequence you will come across obviously totally wrong species names in internet image captions. Anyway, serious tardigrade specialists will tell you that species determination as a rule will not be possible on the basis of just one or two photographs - or on the basis of simple visual comparisons with published tardigrade photomicrographs.

So, what kind of literature will help you to start with practical taxonomy? Let us give it a try and use our maritime Thai tardigrade from  June  as an example.

Will this tardigrade species determination be possible just with with the help of one or two books? No, no way. The literature used in this particular case is shown in the image just below.

Scientific reference literature about marine tardigrades (only a part of which is being shown in the image) is widely spread among many international magazines and has been authored in a babylonian jungle of different languages. As far as the marine species are concerned, their number has virtually exploded during the 2nd half of the 20th century: e.g. Jesuit and tardiologist Gilbert Rahm named just 6 (six) marine species in his tardigrade textbook of 1928, today we count hundreds.

In the case of our Thai tardigrade it is fairly easy to determine the genus: the adhesive toes leave no doubt that it belongs to the marine tardigrade genus Batillipes (cf. the genus key as provided by Renaud-Mornant/Pollock, 1971).

But, when proceeding to the exact Batillipes species determination, literature becomes more scarce. Furthermore, though the genus Batillipes as a whole is highly specific and different from all other tardigrade genera, the differences within the genus are only weakly developed and weakly defined. In fact all those Batillipes species look highly uniform and difficult to discern.

Prof. Ernst Marcus was the intellectual giant among the historic tardiologists. Even today his outstanding illustrations are freely copied (often without reference) and the width of his understanding often appears to be underestimated, in particular by those who are not able to read his original publications most of which are written in German. Ernst Marcus' article about the anatomy and physiology of the marine tardigrades Echiniscoides sigismundi and Batillipes mirus from 1927 is a rewarding literature even today. But it is a fact as well that he knew just a single Batillipes species in 1927 which is not identical with our Thai tardigrade.

Giuseppe Ramazzotti was able to list 15 Batillipes species in his year 1983 monograph. Maria Gallo d'Addabbo describes 24 in the year 2000. As you can tell from those numbers most Batillipes individuals (an estimated multi billion population) was clever enough to remain perfectly hidden in modern times. And at present we have no idea how many further Batillipes species might remian left to detect all over the world's beaches and ocean grounds.

But how should we go on now? Is it worth while to have a closer look at the head of our Thai tardigrade?

Live Thai tardigrade. Front end with head region. Image width ca. 100 µm. Still image taken from one of our videos. Note the circular eye-like spots and the stylet springs.

No, neither stylet springs nor head geometry are helpful in this sitation. And there are no characteristic macroplacoids within the bucchal bulb like with the Macrobiotus tardigrades. Furthermore, the impressive number of sensory head appendices is common to all members of the Batillipes genus. But the hind end of the tardigrade will help us:

Cuticula of the Thai tardigrade. Note the slightly curved conical tail with round edge. Dark field illumination.

A missing tardigrade tail is considered of little importance in tardigrade taxonomy. But its presence and geometry as a rule are highly specific. Thanks to the conical tail of our Thai cuticula we are in the lucky situation to confirm a high resemblance with the species Batillipes similis as described by Erich Schulz in 1955. To our knowledge there is not other marine tardigrade species in literature with a similar conical rounded tail as the one shown here.

In case we would like to proceed further with the taxonomy of this particular case we will have to consult professional literature: foremost the ~ 10 publications resulting from the offical tardigrade symposia, some of them being terribly expensive, some very special. But there can be no doubt that therein contained you will find the utmost tardigrade knowledge densitiy available to everybody.
Those symposium monographs contain lots of so-called "genus reviews" i.e. reviews of the latest state of knowledge for a given tardigrade genus including all relevant literature citations. The tardigrade genus Batillipes received this honour and attention in the year 2000 (cf. article by d'Addabbo et al. in the literature section below).
In this article we can find a further very specific property of the species Batillipes similis: its 4th pair of legs bears two short claws which are different in length, whereas in the regular Batillipes hind leg pair those pairs of shortest claws are equal in length.

'Normal' claw lengths as seen at the 4th pair of legs of a Batillipes tardigrade from France (according to literature different from Batillipes similis !)

Thai tardigrade (cuticula): Different claw lengths at the hind legs, not like regular Batillipes. Sorry, not well visible on the photograph).

One could continue to scrutinize the lateral lobes of the Thai tardigrade cuticula and the spurs on the hind legs. Those properties are as well in accord with the description of Batillipes similis in literature.

Fine structure of the Thai cuticula and conical lobes between the 3rd and 4th pair of legs, considered as typical for Batillipes similis  according to literature.

The long spurs residing on the upper sides of the hind legs are part of the primary species description of Batillipes similis  by Erich Schulz (1955). Oil immersion, extremely oblique illunimation (raking light) for contrast enhancement.

At this point we will stop the determination procedure. Otherwise we might run into the risk of losing our happy naive amateur status!

Literature

Maria Gallo d'Addabbo, Rosanna d'Addabbo, Susanna de Zio Grimaldi: Redescription of Batillipes dicrocercus Pollock, 1970 and Revision of the Genus Batillipes (Tardigrada, Heterotardigrada).
Zoologischer Anzeiger 239 (2000) 329-339.

Hartmut Greven: Die Bärtierchen. Neue Brehm-Bücherei Vol. 537, Lutherstadt Wittenberg 1980.

Ian M. Kinchin: The Biology of Tardigrades. London 1994.

Ernst Marcus: Zur Anatomie und Ökologie mariner Tardigraden. Zoologische Jahrbücher / Abteilung für Systematik, Ökologie und Geographie der Tiere, 53 (1927) 487-558.

Gilbert Rahm: Tardigrada. In: G. Grimpe und E. Wagler, Die Tierwelt der Nord- und Ostsee,
Teil XI.b. 25 pages. Leipzig 1928.

Guiseppe Ramazzotti und Walter Maucci: Il Phylum Tardigrada. Memorie dell'Istituto Italiano di Idrobiologia, 41 (1983) p. 1-1012.

Jeanne Renaud-Mornant, Leland W. Pollock: A Review of the Systematics and Ecology of Marine Tardigrada. p. 109-117. In: Neil C. Hulings (Ed.), Proceedings of the First International Conference on Meiofauna, 1-11 July 1969, Washington 1971.

Erich Schulz: Studien an marinen Tardigraden. Kieler Meeresforschungen, XI (1955) 74-79.

© 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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