Acknowledgements C.W.C. thanks W. Hartman for early insight into questions of arthropod phylogeny and D. Percy for sequencing. J.W.M. and R.W. thank N. Tait, G. Hampson and R. Hessler for help collecting samples. J.C.R. and A.Z. thank
M. Cummings and A. Bazinet for making available grid computing, and the DNA Sequencing Facility at the Center for Biosystems Research, University of Maryland
Biotechnology Institute. J.W.S. was supported by the Maryland Agricultural
Experiment Station. C.W.C. was supported by the Whiteley Center. This work was funded by two programmes at the US National Science Foundation, namely Biocomplexity in the Environment: Genome-Enabled Environmental Science and Engineering, and Assembling the Tree of Life.