Ebay tardigrades (III)

You will remember our previous reports that those exotic mosses that we had received by yellow mail - thanks to Ebay and thanks to classical, true material transporting yellow mail - turned out to be heavily loaded with a sound mixture of different tardigrades, well preserved, in the dry state.

But the numbers of individuals representing the various tardigrade genera were markedly different from what we are used to encounter in Europe. The red, armoured Echiniscus species  were few in species number and low in individual count. And only rarely we did come across individuals to be recognised as the carnivore  Milnesium tardigradum . Instead, Macrobiotus  and Hypsibius were present in large numbers of species and individuals, with a high degree of species variation.

Most impressive were a few giant Macrobiotus tardigrades. They measured more than 700 µm and even 800 µm in length and were strongly pigmented so that our photomicrographs look a little bit like Hamilton style soft-appeal copies.
But please note that this is a purely technical effect due to the tremendous image contrast that simply needed some softening:

Macrobiotus tardigrade from the Canary Islands. Body length ca. 700 µm.

The so-called macroplacoids (calcified structures with a stick-like geometry used for chewing) and microplacoids within the pharynx of the giant tardigrades were structured and arranged as follows:

Pharynx of the giant tardigrades. Arrangement of micro- and macroplacoids.
From left to right are visible: a pair of microplacoids (small grains), a pair of short macroplacoids and a pair of longer macroplacoids with a slight median throttling.
Image width ca. 70 µm.

As in this case everything is a little bit supersized in comparison to other, smaller tardigrade species, we are able to present more anatomic detail in higher resolution. When focusing into the depth of the pharynx we will see a third pair of macroplacoids coming out more clearly. This is one of the rare cases where we can actually imagine that the tardigrade pharynx consists of a tri-radiate volume which has a rather mean tendency to be always partially out of focus. Please remember that it just pretends to be a simple, paired, symmetrical 2D structure but that it is instead a system in urgent need for appropriate 3D representation:

Pharynx of a giant tardigrade from the Canary Islands, other focus position. The red numbering refers to the different placoid pairs. The schematic cross section represents the true geometry of the pharynx which we would see when standing face-to-face with the tardigrade.
Image width ca. 70 µm.

Even very fine structures like the mouth lamellae, normally falling into the reign of scanning electron microscopy can be seen, as well as the central mouth tube supporting bar, which is characteristic for the Macrobiotus genus:

Mouth region of a giant tardigrade from the Canary Islands. The mouth tube bears fine rectangular lamellae. Between the stylets, directly under the mouth tube, the ventral mouth tube supporting bar becomes visible.

The black eye-spots of the giant tardigrade are relatively small. Very nice and only rarely to be seen in this clarity are the muscle strains fixed to an equatorial position at the pharynx, linking to the stylet bases and working in counter-action against the stylet springs:

Head region of a giant tardigrade from the Canary Islands.
A: eye-spot. M: muscles working against the stylet springs.

The claws are typical for the Macrobiotus genus as well:

Symmetrical claw pairs at the rear legs of the giant tardigrade.

Very rare is the attractive red banding on the rear part of the body which probably has to be interpreted as an indicator of considerable age:

Red banding of a giant tardigrade from the Canary Islands (I).

Red banding of a giant tardigrade from the Canary Islands (II).

So, overall, we felt quite confident to attribute our giant tardigrades to the Macrobiotus hufelandi  species. But, sad enough, we were not able to find any of those highly characteristic eggs with cup-shaped egg-protrusions in order to further support our species judgment. So we try to remain appropriately modest and conclude that this giant tardigrade probably belongs to the Macrobiotus genus and that it is at least a close relative to our common Macrobiotus hufelandi species. Remember: tardigrade taxonomy will remain a hopeless endeavour for us amateurs.

© 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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