The body segmentation of oribatid mites from a phylogenetic perspective

摘要

Within the Oribatida both very compact, nearly unsegmented forms and multiply-segmented forms can be observed, making it difficult to identify the most basic body divisions and segmentation. Moreover the basic segmentation type for Acariformes or for mites in general is still unclear. This paper discusses the alternative opinions of van der Hammen (since 1963), which are based on speculative comparative morphology of the Arachnida. The idea of a basic body plan of Acariformes with up to 17 segmentsis rejected and the older schemes of Grandjean (since 1934) appear to be more realistic. The different segmentation patterns within the Enarthronota are discussed and compared with Palaeosomata and other oribatid taxa, against a background of recent phylogenetic analyses. The most probable plesiomorphic hysterosorna in the early Oribatida is a type without segmental notogastral plates but with segmental setation. Basic Enarthronota had some erectile macrosetae on individual sclerites, found in some derived forms as intercalary setae e and f between plates. Nearly homonomous notogastral plates, as observable in Brachychthonioidea and in Haplochthoniidae, are probably secondary constructions.