Molecular phylogenetic analyses support the monophyly of Hexapoda and suggest the paraphyly of Entognatha

Background Molecular phylogeneticanalyses have revealed that Hexapodaand Crustacea form a common clade (the Pancrustacea), which is now widely accepted among zoologists; however, the origin of Hexapodaremains unresolved. The main problems are the unclear relationships among the basal hexapodlineages, Protura(proturans), Collembola ( springtails), Diplura (diplurans), and Ectognatha ( bristletails, silverfishes, and all winged insects). Mitogenomic analyses have challenged hexapod monophylyand suggested the reciprocal paraphylyof Hexapodaand Crustacea, whereas studies based on nuclear molecular data support the monophyletic origin of hexapods. Additionally, there are significant discrepancies with respect to these issues between the results of morphological and molecular studies. To investigate these problems, we performed phylogenetic analyses of Pancrustaceabased on the protein sequences of three orthologous nuclear genesencoding the catalytic subunit of DNA polymerase deltaand the largest and second largest subunits of RNA polymerase IIfrom 64 species of arthropods, including representatives of all hexapodorders.