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A Batillipes sp. tardigrade from Pag island (II)

Tardigrades of the genus Batillipes have been subject of several previous magazine issues, see for example:

Batillipes sp., from the French Atlantic Coast
Batillipes mirus, from the so-called "Kiel Förde" (Baltic Sea)
Batillipes noerrevangi, from Prerow (Baltic Sea)
Batillipes similis, from Thailand

So one might think that the topic Batillipes tardigrades should be closed now. But no, we don't agree. Batillipes tardigrades like the Batillipes from Pag are stunning miracles of miniaturization, always worth a closer look! With its body length of about 0.18 mm the Pag Island tardigrade is 10,000 times smaller than one of us. When looking at volume and weight the relations becomes even more incredible. Volume and weight are below one millionth of the respective values of man! And still those tardigrades are perfectly functioning organisms with everything needed for feeding, sensing and reproduction:

[ Batillipes from Pag: front part of body ]

Batillipes from Pag Island (Croatia): front part of body with complete sensory equipment and those typical lobe formed Batillipes feet.

Well, as we have been showing the front part, why not show the hind scenario as well?

[ Batillipes from Pag Island: hind part of body ]

Batillipes from Pag Island (Croatia): hind part without any tail appendix. Note the two lateral lobes between the third and fourth pair of legs which are of taxonomic importance.

A caudal appendix like the one of Batillipes mirus is completely missing here, so one might be tempted to identify this tardigrade as the species Batillipes acaudatus ("acaudatus" meaning without appendix).
But the tricky point is that the non-existence of a caudal appendix appears to be only a weak taxonomic criterion: according to literature individuums without tail can be found in other Batillipes populations as well (forming exceptions within their species). In any case we should be aware of the fact that the visual appearance of the caudal region alone might not suffice for a thorough species determination.

[ Batillipes from Pag Island: cuticula (1) ]

Batillipes from Pag Island: note the coarse (grainy) structure of the cuticula.

[ Batillipes from Pag Island: cuticula (2)]

Batillipes from Pag Island. Detail view of the cuticula. Fine pores or dots (difficult to tell)?

Experienced microscopists know about the ambiguity of those tiny structures. Any structural detail as small as a typical light wavelength (400 nm - 750 nm) can be deceptive. Under those circumstances some of you might be willing to bet that a given structure has knob type shape wheras others might clearly perceive cavities in the same situation. Arguing often does't make sense in those scenarios. Each interpretation could be the correct one. But as well both interpretations might be wrong. For example the structures in reality could be much more complex, layered, simply unresolved - thus rendering treachery impressions and wrong interpretations.

[ Batillipes from Pag Island: cuticula (3) ]

Batillipes from Pag Island. Detail view of the cuticula. Raking light. Fine nobs?

[ Batillipes from Pag Island: cuticula (4) ]

Batillipes from Pag island: the pharyngeal apparatus is shining through under the cuticula thus providing a means to understand the dimensions.

[ Batillipes from Pag Island: pharyngeal apparatus ]

Batillipes from Pag Island (Croatia): head region with pharyngeal apparatus, mouth tube with root-like or fork-like endings of the mouth tube, stomach with radial muscles, two stylets and fine stylet springs one the left and right side of the mouth tube. Two globular structures reminding of eye spots.

© 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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