Baron Raphael Slidell von Erlanger and the tardigrade tail-plate

Baron Raphael Slidell von Erlanger (1865 - 1897) was a surprisingly multi-faceted personality. It is a pity that there are only a few scarce written sources referring to his biography: that he was a member of a banker family with international affiliations, that he was able to finance his own laboratory at the Heidelberg University, that he married the 'beautiful' Miss Blannerhassett who became very famous later on as Lady Galway in politics, charity and female right affairs - and that he died early.

As a consequence he was no more able to publish some of his tardigrade results as planned and announced in 1895 (missing "Part II").

Baron Erlanger's scientific results are not always in concordance with today's point of view. But there is no doubt that indeed very few scientists were publishing so much in-depth about tardigrade development - before 1900!
Baron Erlanger studied hundreds of tardigrade eggs in various stages of development and ended up with a long series of schematic diagrams illustrating the development steps of the tardigrade egg from the one-cell stage until to hatching.

We have already been mentioning Erlanger's discovery that the tardigrades have delicate   eye-lenses, a finding which he published in 1894. Prof. Reinhardt M. Kristensen from Denmark came up with a similar result in a thin section investigated under an electron microscope, in 1987, about 100 years after Erlanger.

Erlanger used 26 (!) colour (!) illustrations in order to present his viewpoint of tardigrade egg development in 1895. We should keep in mind that even today many scientific publications are only ash-grey black and white at best, some of them moreover in poor printing quality. So, this was really what we today would call an 'innovation':

Schematic cross section through a tardigrade egg (Macrobiotus macronyx).
Original illustration #20 by Baron von Erlanger, 1895 (see literature).
Symbols: cö - coelom, cg - cerebral (upper) ganglion, ug - ventral ganglion, vd - foregut.

When trying tardigrade egg development studies yourself you will inevitably come to the conclusion that this a rather challenging task. Though you might be able to get some insight into the egg from one or another perspective it will be a tough job to draw all the stages in 3D as Erlanger did.
The following photomicrograph shows a mature egg, a few hours before hatching. The bucchal organ is perfectly visible, but everything else, like e.g. a 'v'-shaped two digits' claw is only faintly visible and very difficult to discern.

Mature tardigrade egg (Ramazzottius oberhaeuseri ). Detail view. Overall diameter 60 µm.
Note the bucchal tube, the spheroid pharynx with the so-called macroplacoids.
Live tardigrade, bright field illumination, oil immersion objective 100x/N.A. 1.30.

Erlanger mentions a tardigrade 'tail-plate', which, according to Erlanger is formed at an early stage of development but vanishes later on. He interpretes it as some kind of evolution remains, sort of memory, indicating an earlier evolutionary tardigrade with a fully developed tail.

Schematic cross section through a tardigrade egg of Macrobiotus macronyx .


Abbreviations:
a - after
c - cerebral (upper) ganglion
e^x - legs
go - gonades
ma - stomach
mr - bucchal tube
s - pharynx
sp - tail plate (symmetric, dented)
ug - lower ganglion
vd - foregut

Original illustration #16 taken from
Raphael von Erlanger's
publication of 1895 (see literature).

We do not know whether Professor Ferdinand Richters was aware of Erlanger's vision regarding the tardigrade tail when he discovered the maritime tardigrade Batillipes mirus (1909) - with a conspicuous tail. In any case the maritime tardigrades perfectly fit into Erlanger's line of thought as they might be the ancestors of all terrestric tardigrades (all without a tail).

Links and literature

Further informations about   Lady Galway .

Raphael Slidell von Erlanger: Beiträge zur Morphologie der Tardigraden.
Part I. Zur Embryologie eines Tardigraden: Macrobiotus macronyx Dujardin.
Morphologisches Jahrbuch 22 (1895) 491 - 513. Two colour plates.

© 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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