Interstitial live, within the sand in the oceans (I)

We have already learnt that the waterbear Batillipes mirus lives in the so-called interstitial water volume between sand grains. This is by no means a cosy habitat. In order to survive the tardigrade must be able to crawl on the sand grain surfaces and to move through between the sand grains. It can do this because it is so extremely small. Furthermore the tardigrades must be able to cope with dead end routes between the sand grains.

All animals living within the sand grain system are specialists and they have developed different strategies to survive. E.g. the worm shown below has a kind of route "testing head" and a hind part safeguarding the previous position: a part of it remains in place and another part is checking the situation in front. Furthermore its body is extremely flexible and elastic:

The Batillipes tardigrades have a different strategy in order to cope with difficult pathways. In contrast to their terrestrial brothers and sisters they can move backwards. We hve seen this ability in a  previous issue .

Funny enough Batillipes has eight legs and 48 toes all of which - at least in theory - might be quenched by one of those many huge sand grains. But everyday experience has taught us that those small animals seemingly encounter relatively softer physics - surviving deep falls and developing tremendous power in movement and when working against obstacles.
Though there are many, many sand grains within the ocean and though they might be even moving from time to time, the tardigrade feels safe and healthy between them and as a rule will not be quenched.

In contrast to the worm which is passing trough the holes between the sand grains, avoiding the contact with the sand grain surfaces, the tardigrade is seeking close contact with the sand grains - it appears to be sand grain loving. According to tardiologist Ernst Marcus maritime tardigrades without sand grain might become so desperate that they will commit suicide (but don't become nervous, actually we never did come across this behaviour)! But, in any case the close clinging to the sand grain is obvious:

Batillipes sitting on sand grain. There is no space between belly and substrate.

In particular when seen from top Batillipes looks like a very inconspicuous animal, it is a kind of microscopic, faint shadow. Only the stomach content does interfere with the camouflage - so hungry tardigrades will remain invisible.

Batillipes mirus on a big sand grain. In the center of the image you will see the nice glass housing of a maritime diatom living on the sand grain as well.

Batillipes mirus on sand grain

Lateral lobes at the sides of the Batillipes body make contact with the sand grain like a coat. As a consequence the bruteness of waves will not be able to pass between tardigrade and sand grain surface area. The lobes can be best seen without the sand grain:

Batillipes - stabilising lateral lobes

What are the advantages for tardigrades living within this miraculous "apartment sand"? We will try to explain in our next issue. See you in December!

© 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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