Evasive crawlers (or, alternatively: Croatia IV)

The microscope amateur is well aware of the fact that a second (3rd, 4th) look into the sea water aquarium might reveal a surprise - a perfectly hidden and therefore previosly overlooked creature. In some cases this will be a tardigrade species. On the other hand there is a persistent danger that one might become "tardigrade blind". E.g. if you should think to recognize a tardigrade on the image below it might be better to provide your brain with some fresh oxygen (simply go outside for a walk etc., away from your microscope).

At the first glance one might think that this could be tardigrade clinging to a sand grain. Length of object ca. 0.2 mm.

But, when inspected from a different direction this "tardigrade" turns out to be a foraminifer housing:

Foraminifer housing, as seen from top. Diameter ca. 0.2 mm, very similar to the body length of a typical maritime tardigrade.

In other cases you might be perfectly right about your first eagle-eye impression, look here:

Like one of those classical puzzles. Just find the difference among those two images! Both snapshots are taken from a video. The read arrow is marking the claws of a tardigrade which is approaching from behind, from the backside of the sand grain. A second later a head might follow (looking similar as one of those "Kilroy is watching you" sketches). But it might also happen that the tardigrades decides to retract an go back, hiding behind the sand grain again.

Damit Sie das Ganze besser glauben können, zeigen wir auf dem nächsten Foto (vom selben Video) wieder eine Kralle, diesmal jedoch zusammen mit dem Leib des zugehörigen Bärtierchens, direkt darüber:

Below you will se a detail view of the anterior body of this tardigrade which has not been presented in our magazine yet.

Tardigrade, genus Florarctus. Legs out of focus. Image width ca. 0.15 mm.

Those water bears are really faint, ghost-like creatures, being transparent like ice. Nevertheless the camouflage has its weak points, in particular when the tardigrade is moving with an well-filled stomach on a white sand grain.

Maritime Florarctus tardigrade. It might be difficult under natural conditions to decide where the front and back end is. In this case the head is pointing to the left side. Incident light.

Maritime Florarctus tardigrade crawling on a sand grain. After some brute digital imaging the position of the hind legs can be suspected. It is an almost prefect camouflage by means of transparency.

As usual there will be a follow-up with total views and detail photographs in one of our upcoming issues.

Literature

Hirokuni Noda: A New Species of Marine Tardigrada of the Genus Florarctus (Heterotardigrada, Halechiniscidae) from Japan. 1987.
[available on-line: just try Google "tardigrada new florarctus pdf"]

© 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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