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Croatia (III)

In the   issue 130  we had discussed the cuticula of a marine tardigrade from Croatia. The problem behind was that we had not been able to find the respective living tardigrades when returning from Croatia to our home at Munich.

Possibly our readers will not be able to remember why our most used micro-aquarium for marine tardigrades is called "Rocharium": the micro-aquarium in fact is just a transparent container housing those "Ferrero Rocher" sweets. So, once the sweets are eaten up we are calling the remaining container "Rocharium" in order to keep in mind its double usefulness.

[ "Rocharium" with tardigrades from Croatia ]

Sea water micro aquarium "Rocharium", ca. 15 cm x 8 cm x 7 cm. It contains some very clean sea sand (which, of course, has been kept constantly cool and shaded throughout the transport from Croatia to Germany), just a few millimeters in height. It is filled up with local sea water. This kind of aquarium appears to stay in an almost ideal biological equilibrium appropriate as a tardigrade habitat for at least one year without any change of water and without adding any kind of food.

In spite of the relative tinyness of those micro aquaria we have learnt to accept that several tardigrade species will perfectly prosper within but still might be overlooked when screening through petri dish samples! Compared to tardigrade body length the micro aquarium has a relatively big volume. As mentioned already above we didn't come across a single living tardigrade in the beginning, so we were glad to find a cuticula obviously left back after moulting. But after some months we found the respective living tardigrade as well:

[ tardigrade from Croatia ]

Maritime tardigrade from Croatia with claws, anterior part of body. Image width ca. 0.1 mm.

[ tardigrade from Croatia ]

Maritime tardigrade from Croatia with claws, last pair of legs. Image width ca. 0.07 mm.

Trying to identify the genus

Since the last edition of Ramazzotti's giant tardigrade book (in 1983) apparently no one has been able to provide a comprehensive tardigrade taxonomy book which might serve as the ultimate reference in order to identify all those tardigrade species worldwide. There exist many excellent professional reviews of single tardigrade genera in the scientific literature. But they are spread among many publications and congress papers, some of which might be really expensive and difficult to reach for the amateur.

As a small comfort for all of you we would like to add that also many of the professional biologists appear to have trouble with the tardigrades. For example, Robert Hofrichter's really splendid Mediterranean Sea Book estimates the number of marine tardigrades in the Mediterranean Sea to be a modest "10 ?" (see vol. II/1, 2003, p. 50). As there is a "?" after the number this statement is in perfect accordance with good scientific practice. But it is wrong. The Italian tardiologist Susanna de Zio Grimaldi reported in an earlier publication that she was aware of about 50 different marine tardigrades within the range of the Italian coastline alone.

Clark Beasley's translation of Ramazzotti's tardigrade bible defines a genus with the name Halechiniscus as follows: "Halechiniscidae with legs with four digits, terminating with a sickle-shaped claw, with or without distal spurs; head flattened, with lateral expanded lobes".

Our tardigrade exhibits all the properties mentioned above. And the neighbouring maritime genera obviously do not fit at all. For example, Batillipes and Orzeliscus have round or oval adhesive plates at the ends of their toes. Echiniscoides bears up to eleven claws at each leg, in any case always more than four. Parastygarctus has claws of different length (the two in the middle being the longest ones). Tanarctus  shows cuticular protusions some of which occasionally are bearing "balloons", overall resembling some floral artwork.

A serious tardiologist or professional biologist would probably ask the next question now: and about which species exactly are you talking? Halechiniscus perfectus, Halechiniscus greveni or something else? Our answer is simple: we do not know and, furthermore, it might be not that much important to know. But we feel that in Croatia the number of Halechiniscus tardigrades might definitely be much higher than the number of tourists. And this information could serve as a sort of mental food for the amateur philosophers among us!

By the way: a further tardigrade genus has been hiding in our miraculous "Rocharium". Who else might be able to survive within a spoonful of sand and a cup of sea-water for such a long time and remain undetected? Our tardigrades, yes. We will present this tardigrade genus in one of our upcoming issues. See you.


Robert Hofrichter (Ed.): Das Mittelmeer. Vol. II/1: Bestimmungsführer. p. 50. Heidelberg and Berlin 2003.

Guiseppe Ramazzotti, Walter Maucci: Il phylum Tardigrada. Memorie dell'Istituto Italiano di Idrobiologia. 3rd ed. 1983.

Santiago Villora-Moreno and Susanna de Zio Grimaldi: New Records of marine Tardigrada in the Mediterranean Sea. Zoological Journal of the Linnean Society 116 (1996) p. 149-166.

© 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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