With the exception of Echiniscoides sigismundi (see Sept. 2006 issue)
our findings of maritime tardigrades until now had been restricted to Batillipes tardigrades only.
Yet in the more recent scientific literature there are abundant reports referring to other genera
of maritime tardigrades, a rich world to explore for the microscope amateur, too.
For example BOESGAARD described the claw-bearing maritime tardigrade Actinarctus neretinus
which was isolated from 15kg of wet sand recovered by divers at about 20m depth
at the darkest end of an Australian underwater cave. Well, who dares to ...?
Definitely not us. We decided to look for maritime tardigrades in Mediterranean Croatia instead,
at a depth of about 3.5m and with a sample amout of 20g sand instead of the reported 15kg.
Bay in front of the Aurora Hotel,
Mali Losinj, Croatia. View onto the bay focusing our favourite shallow water
As usual we collected some clean sea sand and shell
gravel containing samples by means of a plastic film container (one
of those from ancient analogue photography times). It contained shell fragments,
sea urchin stick fragments, medium sized sand grain etc.
Back at the hotel we quickly found a "new" tardigrade. Relying on our
previous experience we delayed the better quality photographic documentation
into the future, planning a re-examination when back home.
In fact we had learnt from sand samples containing Echiniscoides and
Batillipes that the maritime tardigrades normally will survive even
in a very minimalistic micro aquarium for weeks and months, probably even years.
But then, back at home in Munich we were terribly disappointed: no tardigrade
at all could be found in those samples any more! After long search we came across
a tardigrade cuticula (left after moulting) - better than nothing:
Cuticula of a tardigrade from the
Losinj island, Croatia, length approximately 150 µm (0.15 mm).
Dark field illumination.
The microscopic study of the cuticula reveals thickened
claw tips (appearing white in the photograph above) and a horizontal pattern
on the dorsal armour plates, which - in contrast to most terrestrial tardigrades
- is not segemented vertically into two parts.
In the bright field photograph (below) the claw tips appear in a darker shade.
Cuticula of a tardigrade from
the Losinj island, Croatia. Bright field photograph.
At higher magnification the dark claw tips appear as
hooks, possibly made up of a different (stronger?) material. They are resembling
Cuticula of a tardigrade from the Losinj island, Croatia, detail.
As we have other workload on the desk at the moment, the taxonomic
discussion will have to be delayed until to the next issue, sorry.
Tom M. Boesgaard and Reinhardt M. Kristensen: Tardigrades from Australian
Marine Caves. With a redescription of Actinarctus neretinus (Arthrotardigrada).
Zoologischer Anzeiger 240 (2001) p. 253-254.
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