Family MACROBIOTIDAE Thulin, 1928

Macrobiotidae: <i>Macrobiotus hieronimi</i>, habitus, bucco-pharyngeal apparatus, leg and egg

Macrobiotidae: Macrobiotus hieronimi, habitus, bucco-pharyngeal apparatus, leg and egg

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Family MACROBIOTIDAE Thulin, 1928

Compiler and date details

September 2013 - Introduction, Dr S. Claxton, Camden, NSW & Dr Reinhardt Kristensen, University of Copenhagen, Denmark

February 2011 - checklist compiled by Jo Wood, South Australian Museum, Adelaide

Introduction

Macrobiotids have two diploclaws arranged symmetrically with respect to the median plane of the leg (2,1,1,2). The two claws on each leg are similar in size and shape. The buccal tube is usually rigid but may have a flexible portion (in the genus Pseudodiphascon); it has a ventral reinforcing bar and the pharyngeal bulb has placoids. The mouth may be terminal or subterminal and is surrounded by lamellae or papulae. The long flap-shaped lamellae probably aid in developing strong suction onto the side of a struggling prey animal such as a nematode or rotifer. In the genus equipped with papulae (Minibiotus), the species are almost all small (less than 400 mm body length), with an antero-ventral mouth and a narrow buccal tube suggesting an herbivorous or grazing habit.

Species may be quite large, with some Macrobiotus reaching 900–1000 mm. Species of Macrobiotus and Minibiotus are the most numerous and diverse in the terrestrial habitats which include mosses and lichens. Species differentiation within these two genera is particularly difficult because of morphological similarity of many groups of species. In both genera, species differentiation is possible using features such as the presence and nature of teeth in the oral cavity, presence and nature of granulation around the claws and presence of teeth on the lunules on the fourth pair of legs (Bertolani & Rebecchi 1993). The eggs provide characters that are often of great assistance in species differentiation. The study by Bertolani and Rebecchi on the Macrobiotus hufelandi group provides a basis for examination of at least nine species in this group found so far in Australia.

The genus Minibiotus has been the subject of considerable research since the discovery, in the Australian fauna, of species the adults of which closely resemble Minibiotus intermedius but whose eggs are considerably different. M. intermedius is considered to be a cosmopolitan species but many citations rely on ‘the characteristic appearance of the adults’ and current work on the Australian species suggests that many such references could be erroneous. The large number of species found provides an opportunity to redefine the genus which was defined (Schuster et al. 1980) only on the presence of peribuccal papulae rather than lamellae and by the presence of a membrane enclosing the egg processes in the single species Minibiotus intermedius (this membrane is absent in many of the new species).

Very little is known of the fauna of soil and leaf litter although the limited work done has provided interesting additions to the fauna. A single species of Calcarobiotus, a recently described genus from Africa (Dastych 1993), has been found in sandy soil on Bribie Island, Queensland. The claws of this animal have a pair of unique, symmetrical spurs which protrude laterally from the bases of all claws. The spurs and transverse cuticular bars below the claws on legs I to III separate this genus from others in the family Macrobiotidae. The free laid eggs have processes like those found in other genera of Macrobiotidae.

The family Macrobiotidae is widespread throughout Australia. The absence of five of the nine known genera probably reflects lack of collection rather than real absence from the Australian fauna.

In addition, unidentified tardigrades thought to represent the genera Calcarobiotus Dastych, 1993 have also been recorded in Australia (Bribie Island, Queensland).