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 property.

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.
Black eyes.

[ 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.

Literature

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.

© 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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