The soil mite genus Conchogneta (Acari, Oribatida, Autognetidae), with new findings from Mongolia

Abstract This work deals with taxonomy, geographical distribution as well as known ecology of oribatid mites of the genus Conchogneta Grandjean, 1963 in the world. The majority of species belonging to this genus is known to be widely distributed in Europe, but only three of them are found in other areas of the northern hemisphere. Most species of Conchogneta are inhabitants of litter of various types of forestas, terricolous and epiphytic bryophytes, epiphytic lichens, and soil of steppe, river valleys, moor, oligotrophic bogs, floodland assemblages etc. A new species, Conchogneta glabrisensillata sp. n. is described, and another species, Conchogneta traegardhi (Forsslund, 1947) is redescribed from the northern and western parts of Mongolia, respectively. Conchogneta is recorded for the first time for the fauna of Mongolia. The species status of Conchogneta dalecarlica (Forsslund, 1947) is discussed. Species descriptions are accompanied with detailed illustrations. Furthermore, a key is provided for the identification of adults of the known species of Conchogneta in the world.


Introduction
The oribatid mite genus Conchogneta is one of seven genera in the family Autognetidae, which was erected by Grandjean (1963) with the type species, Autogneta dalecarlica Forsslund, 1947. Currently, the genus comprises seven nominal species and Specimens were cleared in lactic acid, and a differential interference contrast microscope was used for investigation in transmitted light. Line drawings were made using a camera lucida attached to the compound microscope. Micrographs were taken using a digital camera (Olympus Altra 20) attached to the microscope with single shot.
The morphological terminology used below is mostly that developed over many years by Grandjean (1960aGrandjean ( , b, 1963, and also that by Lions (1975), Norton and Behan-Pelletier (2009). All measurements are given as a range, with the mean in parentheses. Body length was measured in lateral view, from the tip of the rostrum to the posterior edge of the ventral plate, to avoid discrepancies caused by different degrees of notogastral distension. Notogastral length was also measured in lateral aspect (when the dorsosejugal groove is discernable), from the anterior to the posterior edge; notogastral width refers to the maximum width in dorsal aspect. Setal formulas of the legs are given as numbers per segment for appendages (from trochanter to tarsus) and as number per podosomal segment (I-IV) for epimeres. Most species of Autognetidae show the same structure and setation of legs, palps and chelicerae. Therefore, in this work I made detailed descriptions and illustrations of the chelicera and the palp only for one of the studied species.
Integument. Body color yellowish brown to light brown. Surface of body and leg segments with very thin, nearly smooth cerotegument. Integument microtuberculate on tubercles, prodorsum, lateral part of prodorsum, notogaster and around leg acetabula.
Material examined. Holotype (female): Sevsuul valley, Eastern shore of the Lake Hövsgöl, District Khankh, Province Hövsgöl, litter of cool temperate larch forest (Larix sibiricus Ledebour, 1833), 51°16'N, 100°74'E, elevation 1680 m, 08 July 2007, Col. B. Bayartogtokh; three paratypes (females) same data as holotype. The holotype and one paratype are deposited in the collection of the Department of Zoology, National University of Mongolia, Ulaanbaatar, Mongolia, and two paratypes are in the collection of the Senckenberg Museum of Natural History, Goerlitz, Germany. All type specimens are preserved in alcohol. Table 1. Leg setation of Conchogneta glabrisensillata sp. n.

Legs Trochanter
Femur Genu Tibia Tarsus Remarks. Among the eight known species of Conchogneta, only two of them, namely C. traegardhi (Forsslund, 1947) and C. vasiliorum Mahunka, 2006 resemble the present new species in the closely situated structure of prodorsal costulae. However, both mentioned species are different from the new species in the barbed head of sensilli as opposed to smooth sensilli in Conchogneta glabrisensillata sp. n. Moreover they differ in conspicuously barbed notogastral setae in contrast to smooth setae in the new species, nearly straight and thinner prodorsal costulae rather than sigmoid, but thicker costulae in the new species, and different structure of prodorsal tubercles Ea and Ep.
Integument. Body color yellowish brown to light brown. Surface of body and leg segments with very thin, nearly smooth cerotegument. Integument microtuberculate on tubercles, prodorsum, lateral part of prodorsum, notogaster and around leg acetabula.
Remarks. The characters of specimens studied here from Mongolia are match well with the specimens studied by Forsslund (1947), Golosova (1975), Mahunka (2006) and Weigmann (2006). For the sake of completeness, I provide supplementary descriptions with detailed illustrations.

Discussion
The members of the oribatid mite genus Conchogneta are limited to the Northern Hemisphere and are mainly known from moist, warm soils and litter habitats in temperate regions. However, the diversity of this genus is not high, as most of the species were recorded in Europe, except three species, which have expanded distributions in Asia (three species) and North America (one species). Most species of Conchogneta are inhabitants of various type forest litters (beech, birch, fir, spruce, pine, larch), bryophytes (Hypnum sp., Sphagnum sp.) growing on the forest floor, in cave or as epyphytes on hazel trees, as well as soils in river valleys, moor, oligotrophic bogs, floodland assemblages (Weigmann andKratz 1982, Beck andWoas 1991;Huhta andNiemi 2003, Sidorchuk 2009;Toluk and Ayyildiz 2009).
The genus is represented in Mongolia with only two species studied here, and one of them, C. traegardhi is the most widely distributed species of Conchoneta, which is known from Palaearctic and Nearctic regions. It should be noted here that Subías (2010) removed this species from Conchogneta and included it in the genus Autogneta Hull, 1916, without any commentary. However, the structure of the sensilli speaks against the inclusion of C. traegardhi in Autogneta, as the other species of Autogneta have clavate or capitate sensilli in contrast to lanceolate or fusiform sensilli in C. traegardhi, which is typical of Conchogneta (Weigmann 2006). Moreover, according to Grandjean (1963), the genera Autogneta and Conchogneta generally differ in their on-togeny, with the juvenile stages of latter exhibiting spatulate-pateriform setae on both the prodorsum and notogaster.
C. traegardhi is known to be a sylvicolous species, widely distributed in Eurasia and North America, but it is nowhere common (Mahunka 2006). However, it is one of the dominating species in the Mongol Altai Mountains, where I found it abundantly in the litter of the interior of larch forests. It occurs with up to 28 individuals per 125 cm 3 of soil-litter samples collected in the forest interior, but was rarely found in the forest edge or steppe soils, where less than 4 individuals per sample were found. The livestock primarily grazes in the steppe, but also forest margins and less intensively the interior of forests are utilized for pasture. Additionally, were also collected a few individuals of C. traegardhi from the fruticose lichens (Xanthoria candelaria, Rhizoplaca chrysolenca, Parmeliopsis ambigua) growing at the trunk base of larch trees. Most specimens of the present species had food in their gut and food boluses primarily contained fungal hyphae. Heggen (2010) revealed C. traegardhi as an inhabitant of the lower zones of alpine regions in Fennoscandia, but did not find it in the higher alpine zones. Therefore, Heggen (2010) concluded that the distribution of C. traegardhi might be limited by altitude. However, this species is abundantly occurred in the high alpine zone of the Mongoli Altai Mountains at elevation of more than 2300 m above sea level. Therefore, I suggest that the upper limit distribution of this species depends more on the occurrence of forests than on elevation (and, with it, temperature) itself.
The second species found in Mongolia, Conchogneta glabrisensillata sp. n. is quite rare, and was only found in a few samples of single valley out of six studied valleys in the eastern tributaries of Lake Hövsgöl, where many soil, litter and lichen samples were investigated. The valley is a broad, flat valley with steppe vegetation covering the valley bottom and south-facing slopes of mountains on the north side of the valley. The extensive larch forests cover the north facing slopes of the mountains. The valley floor consists of sandy soils and the river sediment is also very sandy. However, the forest floor has a fairly thick litter horizon with black humus rich soil mixed with mosses and lichens. There is relatively heavy grazing with indications of excessive grazing on the south facing slopes, but less grazing pressure in the forest. The new species was collected from litter of a larch forest, and the area is very cold, but one of the moistest regions within Mongolia. While currently known only from forest litter at the type locality, C. glabrisensillata sp. n. probably has a restricted geographic distribution and ecological niche in cold areas.
In the regular update of the checklist of world oribatid mites, Subías (2006) treated the type species of Conchogneta, C. dalecarlica (Forsslund, 1947), as a junior synonym of C. willmanni (Dyrdowska, 1929). Indeed these two species are similar to each other, especially in the widely spaced prodorsal costulae. However, not only these two species, but also several other members of Conchogneta, including C. inundata, C. weigmanni and C. willmanni herzegowinensis, share the costulae laterally placed on prodorsum. The other species have closely placed costulae, which are situated along the center of prodorsum. Thus, all species of Conchogneta can be classified into two groups in respect to their structure of prodorsal costulae.
The following key can be used to identify adults of all known species of Conchogneta.  (Forsslund, 1947)