Long‐branch attraction and incomplete lineage sorting explain the unstable high‐level position of eriophyoid mites in the arachnid tree of life

Abstract Eriophyoid mites (Eriophyoidea) represent a highly diverse lineage of herbivorous arthropods in the Acariformes, including over 5000 named species that are distributed worldwide. However, their high‐level phylogeny within Arachnida remains unresolved. Conflicting phylogenetic placements have been proposed for eriophyoid mites across morphological and molecular datasets. We reconstructed the high‐level phylogeny of Arachnida using genome‐scale datasets and determined the potential systematic error. Our results recovered monophyly of both superorders, Parasitiformes and Acariformes. However, the monophyly of Acari was unstable. The monophyly of all tested orders was also recovered, except for Trombidiformes, which was rendered paraphyletic by the monophyletic Eriophyoidea lying outside the Trombidiformes and forming a sister group to the remaining Acariformes species. The unstable position of Eriophyoidea within Acariformes may be influenced by both long‐branch attraction and incomplete lineage sorting. We propose that Eriophyoidea lies at the basal position of Acariformes, forming a sister group to the remaining Acariformes mites. Our findings resolve the high‐level placement of four‐legged mites and shed new light on the arachnid tree of life.