Last egg-day and first life-day of Milnesium tardigradum

The tardigrade  Milnesium tardigradum  can be found almost everywhere on earth and can be easily kept in a micro aquarium for a few weeks. Last December  we witnessed how Milnesium babies hatched within their cuticula shelter and made their way out into freedom. The following microphotographs show the develoment of an artifically isolated Milnesium egg. The first four image block shows the egg at the day of hatching, the second the same individuum at its first day of life outside the eggshell.

 Milnesium, egg.

 Fig. 1

 Fig. 2

 Fig. 3

 Fig. 4

When seen from aside the Milnesium babies lie rolled up within their eggs like anxious woodlouses (Fig. 1). When focussing more deeply into the egg (Fig. 2) we will notice the broad mouth tube indicating the carnivore behaviour and the pear shaped pharynx with its radial muscle pattern. Even the normally straight line from mouth tube to pharynx is slightly bent in order to fit tightly into the eggshell. The claws are already fully developped as well but not easily visible in the photograph (Fig. 3). In Fig. 4 two black eye-spots seem to make eye-contact with us. The diameter of a Milnesium egg is about 80 µm.

 Milnesium, 1st day

 Fig. 5

 Fig. 6

 Fig. 7

 Fig. 8

After hatching we will become aware ot the fact that the cuticula is drastically oversized thus allowing the baby to grow considerably before a moulting phase will become necessary (Fig. 5). Otherwise it might have not enough fat resources and starve during the first moultuing phase. The claws at the last pair of legs are huge in relation to the overall body size (Abb. 6), the spherical floating storage cells in the body fluid still very small. A view of the mouth opening reveals the hexagonal array of mouth papillae (Fig. 7) and it becomes obvious that they are vary different in size, with Fig. 7 showing only the three upper (dorsal) papillae.
Also the two cheek papillae can be seen already in this early phase of life (again Fig. 7).
Fig. 8 presents the bucchal apparatus, already fully developped, with pear shaped pharynx, stylets, stylet supports and the broad bucchal tube. We have already learnt that Milnesium can make use of it and devour tiny tardigrades as a whole thus exhibiting a mother-nature brute  carnivore  behaviour. From the first moments in their lifes the Milnesium babies check on everything in their environment in order to find out whether it might serve as nutrition.

© 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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