Phylogeny of opilioacarids and their affinity with the other mites
1970 - Volume: 12 Issue: 3 pages: 465-473
La phylogenese des opilioacarides et leurs affinites avec les autres acariens. - Because of the lack of paleontological data, conclusions on the phylogeny of Opilioacarida are obtained only by phyletic weighting of characters of recent species. Up till now eight valid species have been described, whilst the descriptions of seven new species are in preparation. These species are classified in four genera. The geographie distribution is especially gondwanian. Starting from a fenetic classification obtained by comparison of species and homologous structures, six pairs or series of characters can be distinguished to which an important phyletic value is attributed. By paying special attention to shared possession of derived characters, a cladogram can be constructed. By means of this cladogram an archetype (in the sense of a synthetic type, combining the ancestral characters of a monophyletic taxon) can be constructed. The phyletic divergence is determined by comparing each genus with the archetype. When the divergence is known, the dendrogram can be constructed representing the phylogeny of the Opilioacarida. One of the most important conclusions from the dendrogram is that on the depilation of the opisthosoma in different genera by parallel evolution. In comparing the Opilioacarida with other groups of mites, it appears that there is a distinct relationship with the Holothyrida; bath groups, without doubt, belong to the Anactinotrichida. In spite of the shared possession of a number of primitive characters, Opilioacarida are widely separated from the Actinotrichida, especially because of the presence of sternal taenidia, and the absence of a podocephalic canal. It is demonstrated that in a common ancestor of Anactinotrichida and Actinotrichida (in case the mites are monophyletic), sternal taenidia as well as podocephalic canal must have been absent; this means that the gnathosoma of this ancestor was still at the beginning of its evolution, and the ancestor itself still at the very beginning of its evolution as mite.
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