Our Taxonomy series - in cooperation with Rolf Schuster*
Episode #2: Minibiotus intermedius

Fig. 1: Full portrait of a Minibiotus intermedius. Brightfield. All photomicrographs in this issue depict permanent specimens from the collection of Rolf Schuster.

Minibiotus intermedius was first described by the zoologist and social Darwinist Ludwig Plate [Wikipedia] in 1888. The specimens he examined came from Chile and the area around Marburg, where he received his habilitation.

Plate believed that Macrobiotus intermedius (as the newly discovered animal was originally called) was intermediate in its characteristics between Macrobiotus hufelandii and Macrobiotus oberhaeuseri (now called Ramazzottius oberhaeuseri), hence the epithet intermedius. Minibiotus intermedius was transferred from the Macrobiotus group to the Minibiotus group in 1980.

When describing animals (and plants) for the first time, a precise description of the characteristics typical of that species must be provided and documented, for example, with photographs. In the case of tardigrades, individual specimens are preserved in permanent slides. These then serve as a reference for researchers. In case of Minibiotus intermedius the original material was lost. Therefore, Kaczmarek et al. (2022) described the species again. The following information on Minibiotus intermedius is based on the monograph by [Dastych 1988] - see literature below.

Minibiotus intermedius (length 124 to 266 µm) has a smooth, white cuticle, sometimes with brown pigment, and conspicuously large eyes. The rounded pharynx shows rows of three small, rounded macroplacoids and extremely tiny microplacoids (figs. 2 and 3).

Fig. 2: Enlarged detail from fig. 1. Visible is a pharyngeal bulb, roughly spherical, slightly oval in appearance, with numerous, very fine, radially arranged muscle fibers, as well as the pea-shaped macroplacoids arranged in rows of three. The tiny microplacoids are just barely visible to the left of the macroplacoids.

To achieve optimal detail resolution of the pharyngeal bulb, we had to work at maximum objective apertures, filter the white light from the microscope illumination, and then, after converting the image to black and white, fine-tune the contrast a bit. This made the macroplacoids even more clearly distinguishable as separate anatomical elements.

Fig. 3: Image taken as in figs. 1 and 2, but with even greater clarity achieved through the use of a strict green filter (and additional black and white conversion). Note also the particularly large eyespots in this species.

The rigid mouth tube appears straight in top view and curved in side view (fig 4).

Fig. 4: In the side view, it can be seen that the mouth tube curves strongly on the ventral side, towards the mouth opening.

The claws are very small (fig. 5 and fig. 6), showing slightly more detail under a light microscope only at the highest resolution (using oil immersion and oblique light).

Fig. 5: Close-up of a pair of foreleg claws. The outer and inner claws are - like all claws in Minibiotus intermedius - approximately the same size.

Fig. 6: Fourth pair of legs of Minibiotus intermedius, ventral perspective. The species-typical, symmetrical uniformity of the relatively small claws can be seen on the right leg in the image. The claw on the far left is rotated by approximately 90°, thus demonstrating the different appearance of such claws depending on their orientation under the microscope.

The eggs are equipped with so-called extrusions and are laid freely. Minibiotus intermedius is frequently found, mostly in soil and bark mosses.

Notes and literature

(*) Dr. Rolf Schuster, tardigrade specialist, partner and co-author of this taxonomy series, will be happy to advise you on more in-depth taxonomic questions and on the identification of tardigrades you have found. Simply send an email to Rolf Schuster !

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Hieronim Dastych, The Tardigrada of Poland. Monografie Fauny Polski 16, 1-255. 1988.

Hartmut Greven, Die Bärtierchen. Wittenberg Lutherstadt 1980.

Kaczmarek, L.; Kayastha, P.; Roszkowska, M.; Gawlak, M.; Mioduchowska, M.,
Integrative Redescription of the Minibiotus intermedius (Plate, 1888) — The Type Species of the Genus Minibiotus R.O. Schuster, 1980. Diversity 2022, 14, 356.
https://doi.org/10.3390/d14050356

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

Wikipedia, Ludwig Plate (zoologist)

© Text, images and video clips by  Martin Mach  (webmaster@baertierchen.de).
The 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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