Dactylobiotus dispar (II)
In the last issue we had spotted the tardigrade Dactylobiotus dispar
in one of its favourite places, the underside of a water lily leaf .
It appeared to be a faint ghost, not so much an actually living animal and was well hidden
within the water lily leaf structure. So we will better continue without the
disturbing background pattern:
A Dactylobiotus dispar tardigrade,
not yet fully grown up.
Body length ca. 300 µm.
"Looks like a typical Macrobiotus moss eutardigrade"
you will possibly think after a first glance and you would not be fully wrong.
Only when using stronger magnifications we will notice some details
which convinced the scientists in the year 1980 to define a new genus
Dactylobiotus which was separated from the big genus
Macrobiotus . A strong sclerified
linking bar at the base of the claws has been recognised as a unique taxonomic
Tardigrade Dactylobiotus dispar,
last pair of legs.
The red arrow indicates the linking bar which was
used to define the genus Dactylobiotus and to separate it from the existing
genus Macrobiotus. Body length ca. 500 µm.
There are only a few species within the genus Dactylobiotus,
as a consequence it might be possible also for us amateurs to come
close to a species determination. First we will have a look at the anterior
part of the body:
Tardigrade Dactylobiotus dispar,
anterior part of the body.
[ For an explication of the specific terms please refer to Macrobiotus
Two macroplacoids, the first of which looks like broken.
Komma is missing.
Broad curved stylets with a strong base (furca).
Oval pharynx, ca. 80 µm long.
Dactylobiotus dispar has two characteristic bumps (elevations) at its backside,
between the third and fourth pair of legs. They are not photographed easily but
are conspicuous when looking at a living animal.
One of the bumps on the backside of
the tardigrade Dactylobiotus dispar as seen from aside (arrow). The second bump
is hidden behind the first.
The visual appearance of the eggs of Dactylobiotus dispar
is an important taxonomic criterion and helps to distinguish related species
like Macrobiotus macronyx and Macrobiotus ambiguus .
The eggs are deposited freely, not in the shed cuticula. Their maximum diameter
is about 90 µm.
Egg of the tardigrade Dactylobiotus dispar .
Maximum diameter including the protrusions: 90 µm.
Furthermore there are the mouth lamellae. According to
Walter Maucci Dactylobiotus dispar should have 10 of those lamellae.
It might turn out to be difficult to count the lamellae under the light microscope.
We suggest to leave this activity to the taxonomic specialists. Please keep in mind
that the tardigrades do not like to be quenched or turned between slide and cover glass
just in order to count their lamellae.
Fine lamellae surround the mouth opening
of Dactylobiotus dispar .
According to the scientific literature
10 lamellae are considered to be characteristic for this particular species.
In the next issue we will see that some of the Dactylobiotus dispar
females apparently check out their environment in order to find an optimum
shelter for the deposition of their eggs.
Schuster, R.O., Nelson, D.R., Grigarick, A.A., Christenberry, D.:
Systematic Criteria of the Eutardigrada. Transactions of the American
Microscopical Society 99 (1980) p. 284 - 303.
Maucci, W.: Tardigrada. p. 231. Bologna 1986.
Marcus, E.: Tardigrada. p. 187. Berlin 1936.
Morgan, C.I., King, P.E.: British Tardigrades. p. 77. London 1976.
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Martin Mach (firstname.lastname@example.org).
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