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Two Rhagidiidae, Brevipalpia minima Zacharda, 1980 and Hammenia macrostella Zacharda, 1980 were retrieved from forests of Belgium. This gave us the opportunity to assess the role of parataxonomy and molecular data in identifying soil mites and to emphasize the importance of morphological characters. © 2009-2011 ACAROLOGIA.

Quantitative studies of mite communities in endogeic and cave ecosystems are scarce. In this paper, we tested and validated the hypotheses that (1) deep soil and cave mite communities are distinct and (2) that species composition is more variable in caves than in deep soils. Mites were sampled in May, November, and January at 15-20 cm depth in three temperate forest soils and at the surface of sediments in two caves situated directly below two of these soils. Endogeic mite densities ranged from 77 to 225 individuals/dm(3) vs. 9 to 43 in caves. Organic matter was found to be the main factor correlated to density in soils while flooding are thought to profoundly affect cave communities: it introduce accidental species that eventually die without breeding, inducing a sharp seasonal variation in mite density. Mite richness estimates amounted to about 80 species in most locations. (1) Cave populations were distinct from endogeic ones and migration between those habitat compartments is thus supposed to be infrequent. (2) Both the fragmented structure and flooding that lead to the addition of accidental species, are invoked to explain the larger variability of cave communities compared to soil communities. (C) 2005 Elsevier SAS. All rights reserved.

We studied adaptations to subterranean environments in Acari. Mite populations of two caves and of the mineral horizon of soil from three forest sites were analysed. In the soil, body length was limited by the pore size. The proportions of (i) predators, (ii) phoretic mites, and (iii) primitive oribatids were higher in caves. This was potentially explained by (i) polyphagy or predation on other groups and reduced interspecific competition, (ii) the fragmented structure and liability to flooding of the cave habitat, and (iii) the higher humidity in caves. Adaptations to dry habitats probably greatly influenced the evolution in Oribatida. It is proposed that numerous mites colonized caves directly from deep soil without a surface stage.

The determinants of mite diversity in soil and the reasons why so many species coexist are poorly understood. There is evidence that niche differentiation (i.e. microhabitat complexity) in the titter layers of forest floors is important, however, little is known for deeper horizons since mite density and diversity in deeper soil layers have been rarely studied. In order to address this dearth of information, we collected microarthropods from both the forest floor and the mineral soil to a depth of 1 m in two deciduous forest locations. The density exceeded 8 x 105 microarthropods M-2 in one location, and a number of individuals were collected from deep in the soil. No species was exclusively living in mineral horizons. Measurements of porosity spectrum, pH, water content, total C and total N were made at each depth and related to mite diversity and species richness. Meso- and microporosity were strongly correlated with species distribution while macroporosity and pH were correlated to density and species richness. (C) 2004 Elsevier GmbH. All rights reserved.

Although the soil is a major reservoir of biodiversity, our knowledge ofits mesofauna remains scanty, especially in the tropics. The diversity oforibatids (149 adult oribatid mite species) is analyzed for the first time in anAfrican soil and studied in three ecosystems of a regressive sere: forest,woodland and savanna. Savanna is the richest ecosystem overall, with 105collected species, whereas the mean number of species per releve (αdiversity) is highest in forest. In barren soils, the number of species observedalong the sere drops regularly from the typical forest to the savanna. However,this pattern is complicated by other factors acting at different scales. Theincrease of oribatid richness parallels that of habitat complexity, from barrensoil to termitaria colonized by grasses and trees. On a finer scale, soilproperties also influence species richness, either indirectly through density(water content) or directly (total nitrogen, C/N ratio, organic matter), buttheir importance varies in relation to seasons. Most exclusive species (nearly90%) are housed in the two extreme types of vegetation, forest and savanna. On afiner scale, two habitats, the typical forest and the termitaria in the savanna,are remarkable by the number of exclusive species and are worth protectingthrough effective conservation measures.

The study of soil microarthropod biodiversity is illustrative of problems that are related to other soil organisms (fungi, for instance) or that can be found in other environments (canopy, oceanic sediments, hosts accommodating parasites, etc.). Indeed, the contribution of the soil fauna to global biodiversity remains an enigma even though, in recent years, it has received considerable attention. Our contention is that the debate on soil biodiversity will remain open - and even sterile - as long as adequate sampling methodologies are not set up, critically evaluated and largely used. First, a critical review of the sampling strategies used for soil microarthropods is presented. In addition to an extensive compilation of publications on extraction method efficiency, articles from two journals devoted to soil biology are compared for two five-year periods (before and after Erwin's papers and before and after Rio). The most frequently used extraction methods (over 90% of studies) have a poor numerical efficiency (e.g. 7-26% for the Berlese-Tullgren funnels) and also are selective with respect to their efficiency for certain taxa (variable taxonomic and functional efficiency), 75% of studies are restricted to the upper 10 cm of soil and therefore overlook largely the microarthropod populations. some groups are often neglected, however diversified they are, and the taxonomic resolution tends to become impoverished in recent years. In the second part of our study, the importance of bias induced by inadequate or restricted sampling strategies on biodiversity estimates is evaluated: densities are dramatically underestimated (down to 14 times less); conversely species aggregation, a factor advocated to explain the existence of numerous soil species, is overestimated; some functional groups may be quite overlooked; the species distribution along a gradient deduced from the sampling may be rather different from that really existing in the soil and interfere with the evaluation of beta-diversity; species richness is often crudely underestimated (down to 50%). Overall, at most 10% of soil microarthropod populations have been explored and 10% of species described. Obviously, much has still to be done to evaluate soil microarthropod biodiversity and a fortiori understand the mechanisms underlying it. Improving and renewing the soil sampling strategy is thus a prerequisite to any real advance in our knowledge of this fascinating and obscure domain.

Soil oribatid mite communities from three vegetation types (forest, woodland and savanna) are described in Luiswishi (high Shaba, Zaire) and 151 species were recorded. Oribatid communities are organized along a successional gradient which parallels the regressive sere defined by phytosociologists and going from the dense forest (''muhulu''), the local climax, to the savanna, passing through the woodland (''miombo''). Within this gradient, oribatid communities may vary depending on the habitat (presence of grass, high termitaria). The impact of seasons (dry vs. rainy season) is weak in the forest but drastic in savanna. The various soil oribatid communities are related to man's activities since the regressive sere results from repeated burnings and associated agricultural practices.

International audience; Apart from a calyptostatic prelarva, the ontogeny of spider mites is limited to one six-legged immature followed by three eight-legged instars. The usage consists in naming them: larva, protonymph, deutonymph and adult. In this study, the "missing stase" and different associated hypotheses are explored using diverse approaches: light microscopy, electronic microscopy, comparative chaetotaxy, ontogenetic trajectories, and interspecific comparisons. It turns out that the imago (new name for the last stase) is missing in Tetranychus urticae and that its post-embryonic development may be summarized as follows: prelarva (calyptostase), larva (six-legged stase), protonymph (eight-legged stase), deutonymph (eight-legged stase), tritonymph (with paedogenesis, i.e. precocious development of sexual maturity). The respiratory role of the prelarva is emphasized. The current terminology of post-embryonic development is confusing as it pertains to three approaches: the state or form description, the instar standard and the stase paradigm.

Different approaches to biodiversity yield global totals as small as 3 million or as large as 80 million species. Erwin's calculation and estimation leads to an estimate of ca 30 million species and relies on four assumptions of which one concerns the ratio between the number of canopy insects and those found elsewhere, especially in the soil. A short survey of the microarthropods living in coastal sand dunes and collected with a new flotation method yielded amazing results. In spite of the severity of the habitat (low organic matter content and extreme dryness), the density of microarthropods varied between 175 000 and 1 400 000 individuals per square metre, i.e., densities 3 to 10 times higher than densities usually observed in any other type of soil. A total of 31 species was recorded, most undescribed and smaller than 200 μm. The consequences of these findings on the estimation of the number of species are discussed. It is suggested that the soil, including the deepest horizons and the rhizosphere, might constitute a huge reservoir for biodiversity.

Camisia carrolli n. sp., an oribatid mite collected in Oregon, U. S. A., is described. This species living on Douglas fir is compared with two other arboreal species: C. segnis (Hermann) and C. horrida (Hermann). The description and comparisons deal with both the adult and immatures. Specific criteria for determining immatures of Camisia are explored.