Maximum likelihood tree inferred from amino acid residues deduced from 12 mitochondrial protein-coding genes of 30 arthropods and 4 non-arthropods. The pycnogonids Achelia bituberculata and Nymphon gracile appear within the monophyletic Chelicerata with high node confidence values. Scorpiones are placed as the basal arachnid group. The inclusion of Pycnogonida within Arachnida is shown in this tree. The monophylies of Pancrustacea (Crustacea plus Hexapoda) and Myriochelata or Paradoxopoda (Myriapoda and Chelicerata) are strongly supported. The numbers above/below the branches indicate the node confidence values: BPML (bootstrap proportion in the maximum likelihood analysis), BPBI (bootstrap proportion in Bayesian inference) and BPP (Bayesian posterior probability) in order. The tree was obtained from a final alignment 2232 aa sites in length (refer to Materials and Methods for more detailed information). The log likelihood value of the best tree is -72575.641555. For more detail information about the taxon, refer to Table 1.