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/zm. 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.
The acarofauna associated with Carabidae (Coleoptera) in Belgium is studied. About 1000 mites were collected from 19 sites from 155 carabid beetles belonging to 21 species and 8 genera.The mites belonged to 12 species, 8 genera, 8 families and 3 orders. All mites were found beneath the elytra of the beetles except the hypopi of the Histiostomatidae which were found attached to the body. A new species ofAntennoseius, A. calathi n. sp. (Ascidae), is described from Calathus micropterus and Pterostichus diligens. More than half of the mites of our collections were deutonymphs belonging to 2 species of the genus Halodarcia Karg (Halolaelapidae) i.e.H, incideta Karg, 1969 and Halodarcia sp.
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