The genus Macrobiotus (tardigrada)

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Macrobiotus tardigrade. Anterior part of the body.
Image width ca. 150µm

The definition of the genus  Macrobiotus  was established by Schultze. In 1834 he described the first species of the genus Macrobiotus, Macrobiotus hufelandi.
Have a look at Schultze's original text  here !

The most important characteristic property of Macrobiotus tardigrades are the kind of branching and the symmetry of the claws:

Claws of a Macrobiotus tardigrade. After Marcus (see literature)

The parts of the pharyngeal apparatus are important for taxonomy as well:

Fig.: Pharyngeal apparatus of a Macrobiotus tardigrade (Macrobiotus cf. hufelandi).
Comments:
(1) Macroplacoids: calcified parts within the pharyngeal bulb serve as chewing instruments.
Form and number of the macroplacoids can be recognised easily and are often used to distinguish among different species
(2) So-called comma, can be absent in some species
(3) Mouth tube. The mouth tube of a Macrobiotus is always approximately straight, unflexible and wide.
(4) Macrobiotus tardigrades have strong curved stylets which serve as a tool to pierce plant cells see video: stylets in action
(5) Stylet sheaths. The stylet sheaths have slits at their front ends, so the stylets are guided through them to the outside world.
(6) Mouth opening, here a round 'kissing' mouth;
(7) Muscles of the pharyngeal bulb
(8) Stylet supports. The stylet supports act like springs working against muscles which are fixed to the pharyngeal bulb

Macrobiotus tardigrades as a rule move much more quickly than e.g. the red, armoured echiniscus tardigrades (see title image of the Water Bear web base). Their body colour is white or brownish in incident light, transparent in transmitted light, never red. The stomach contents can be green. Walter Maucci (see literature) counts about 93 Macrobiotus species worldwide.

Typical visual appearance of a Marcrobiotus tardigrade.

© Photomicrographs and illustration (following Marcus) by  Martin Mach

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Literature:

The probably best and most modern taxonomic book is:

G. Ramazzotti und W. Maucci: Il Phylum Tardigrada. Memorie dell'Istituto Italiano di Idrobiologia 41 (1983) p. 1-1012 [in Italian language only, but there exists an English translation by professor Clark W. Beasley].

Ernst Marcus: Bärtierchen. p. 6 (1928)

Walter Maucci: Tardigrada (vol. XXIV in the series Fauna d'Italia). p. 180. Bologna 1986.