"This one is really yellow!" - Macrobiotus coronifer and very close relatives

In the year 1859 the famous German zoologist Christian Gottfried Ehrenberg (1795 - 1876) published an article with the title: "Contribution to the assessment of persisting life in Alpine heights up to 20,000 feet".
He did invest considerable effort in the illustrations. E.g. his engraving showing Macrobiotus furcatus from the Monte Rosa mountain measures 26 cm in width (!). But still - remember, we are in the 19th century - it is a b&w illustration. Ehrenberg is compelled to add some verbal comment:

The colour of the fresh specimen is vividly yellow.

What does he mean by  fresh  specimen? Tardigrade literature in general tends to neglect colour. Scholarly biology has a strong tendency to fix any living cell by means of formaldehyde thus preserving most structural details - hopefully. One of the first victims in the process of fixation is colour. So, if the colour is not documented in some way before the fixation, it will be lost. On the other hand, many tiny structural details like the fine pattern of the cuticula will persist in the permanent preparation for decades and therefore will be preferred in species characterisation.

The famous Ehrenberg did not fail to note the intensively yellow colour and we will show it to you now:

Intensively yellow tardigrade, typically found in mountain regions,
e.g. the Bavarian Alps. Still image captured from a video film.
Body length ca. 600 µm.

Ehrenberg continues:
The claws ... have an almost perfectly disc-shaped dented base ... the exact geometry of which was difficult to determine.

We have looked at the feet of our Bavarian specimen as well and did encounter similar (?) focusing problems:

Intensively yellow tardigrade. Detail: claws of the last pair of legs.
Still image from a video clip. Dark field illumination.

Intensively yellow tardigrade. Same detail as before, slightly higher magnification. Bright field illumination.

Ehrenberg added an illustration of the eggs which are highly characteristic and which look identical as those of our yellow tardigrade:

Intensively yellow egg of the yellow tardigrade.
Maximum diameter ca 150 µm.

And here is a view of the pharyngeal bulb:

Same tardigrade as before. Detail showing pharyngeal bulb, bucchal tube and stylets. Two spheroid macroplacoids, no Komma.

All the details on our photomicrographs look identical to those on the Ehrenberg Macrobiotus furcatus illustrations. But in 1928, when describing the properties of the species Macrobiotus furcatus the tardiologist Ernst Marcus doesn't mention the conspicuous colour at all.

In 1903 Ferdinand Richter claims the existence of a new species now called Macrobiotus coronifer . It has exactly the same properties as Macrobiotus furcatus, with chrome yellow storage cells in incident light and ochre storage cells in transmitted light. Again, the species name seems to be as fugitive as the colour of the fresh specimen: in 1981 Macrobiotus coronifer is going to be renamed to Adorybiotus coronifer .

Don't panic, tardigrade taxonomy is a full-time job and we are amateurs.
In the next issue we will show Ehrenberg's fine original illustrations. Stay tuned!

Literature

Christian Gottfried Ehrenberg: Beitrag zur Bestimmung des stationären mikroskopischen Lebens in bis 20,000 Fuß Alpenhöhe. p. 455. Abhandlungen der Königlichen Akademie der Wissenschaften, Berlin 1859.

Ernst Marcus: Bärtierchen. p. 135 [description of Macrobiotus furcatus]. Jena 1928.

Ernst Marcus: Tardigrada. p. 153 [description of Macrobiotus furcatus]. Berlin 1936.

Ferdinand Richters: Nordische Tardigraden [description of Macrobiotus coronifer on p. 171].
Zoologischer Anzeiger 27 (1903) 168-172.

Hieronim Dastych: The Tardigrada of Poland. S. 69 - 71 [Description of Adorybiotus coronifer, with excellent drawings]. Warsaw 1988.

Walter Maucci: Fauna d'Italia: Tardigrada. p. 227 - 230 [description of Adorybiotus coronifer]. Bologna 1986.

Walter Maucci, Giulio Ramazzotti: Adorybiotus gen. nov.: nuova posizione sistematica per Macrobiotus granulatus Richters, 1903 e per Macrobiotus coronifer Richters, 1903 (Tardigrada, Macrobiotidae). Mem. Ist. Ital. Idrobiol., Pallanza 39 (1981) 153 - 159.

© 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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