Mites from a Land of Ice and Snow

Mycobates sarekensis, from Siepel & Dimmers (2010).

The Arctic tundra is not an inviting place. Cold winds sweep through a forebidding landscape, unhindered by forest. In places, patches of bare rock can be seen, with no vegetation able to retain a foothold other than hardy lichens. And yet even here you can find an entire ecosystem in place if you look closely enough.

The animal shown at the top of this post is an oribatid mite of the genus Mycobates, a group of about 35 species belonging to the family Punctoribatidae (sometimes referred to as Mycobatidae). These are sturdy, stocky oribatids with a body that is oval in cross-section, with a length generally around the half-millimetre mark (Seniczak et al. 2015). Characteristic features of Mycobates include pteromorphs (triangular outgrowths of the body wall that hang down over the bases of the legs) that are hinged by a line of weaker cuticle so they can be moved up and down, a convex pedotectum I (another protruding shelf, this time on the underside of the body shielding the base of the first pair of legs) and overlapping lobes at the back of the body where the dorsal shield (the notogaster) overhangs the edge of the venter (Behan-Pelletier 1994). Their legs are curved inwards towards the body, and the dorsal setae are usually smooth, without barbs, and flexible (Seniczak et al. 2015).

SEM of Mycobates beringianus from Behan-Pelletier (1994). Note the cluster of pores visible as a lighter patch on the side of the notogaster; these are secretory or respiratory structures.

Many of these features are suited to the preferred habitat of a number of species in the genus: burrowing through the thalli of lichens (which are both home and food). Mycobates species are found in cooler boreal and alpine habitats. Species found in more Arctic habitats, such as the tundra-dwelling M. sarekensis, are found close to ground level (in the tundra, there's not many other levels to be found at). In more temperate regions, they are often arboreal, crawling about on the trunks and branches of trees. Some species have been found in association with mosses as well as lichens; many of the northern species are able, snuggled as they are in their moss or lichen hosts, to live in microhabitats too dry for many other invertebrates.

REFERENCES

Behan-Pelletier, V. M. 1994. Mycobates (Acari: Oribatida: Mycobatidae) of America north of Mexico. Canadian Entomologist 126: 1301–1361.

Seniczak, S., A. Seniczak & S. J. Coulson. 2015. Morphology, distribution and biology of Mycobates sarekensis (Acari: Oribatida: Punctoribatidae). International Journal of Acarology 41 (8): 663–675.