1. Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Avenue, Cambridge, Massachusetts 02138, USA
2. Australian Museum, 6 College Street, Sydney, New South Wales 2010, Australia
3. Division of Invertebrate Zoology, American Museum of Natural History, Central Park West at 79th Street, New York, New York 10024, USA

Correspondence to: Gonzalo Giribet¹ Correspondence and requests for materials should be addressed to G.G. (e-mail: Email: ggiribet@oeb.harvard.edu). GenBank accession codes for the new sequences are AF370781–AF370876.

Abstract

The interrelationships of major clades within the Arthropoda remain one of the most contentious issues in systematics, which has traditionally been the domain of morphologists^{1, 2}. A growing body of DNA sequences and other types of molecular data has revitalized study of arthropod phylogeny^{3, 4, 5, 6, 7} and has inspired new considerations of character evolution^{8, 9}. Novel hypotheses such as a crustacean–hexapod affinity^{4, 10, 11, 12} were based on analyses of single or few genes and limited taxon sampling, but have received recent support from mitochondrial gene order¹³, and eye and brain ultrastructure and neurogenesis^{14, 15}. Here we assess relationships within Arthropoda based on a synthesis of all well sampled molecular loci together with a comprehensive data set of morphological, developmental, ultrastructural and gene-order characters. The molecular data include sequences of three nuclear ribosomal genes, three nuclear protein-coding genes, and two mitochondrial genes (one protein coding, one ribosomal). We devised new optimization procedures^{16, 17} and constructed a parallel computer cluster with 256 central processing units¹⁸ to analyse molecular data on a scale not previously possible. The optimal 'total evidence' cladogram supports the crustacean–hexapod clade, recognizes pycnogonids as sister to other euarthropods, and indicates monophyly of Myriapoda and Mandibulata.

1. Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Avenue, Cambridge, Massachusetts 02138, USA
2. Australian Museum, 6 College Street, Sydney, New South Wales 2010, Australia
3. Division of Invertebrate Zoology, American Museum of Natural History, Central Park West at 79th Street, New York, New York 10024, USA

Correspondence to: Gonzalo Giribet¹ Correspondence and requests for materials should be addressed to G.G. (e-mail: Email: ggiribet@oeb.harvard.edu). GenBank accession codes for the new sequences are AF370781–AF370876.