Molecular analyses have typically found crustaceans to be non- monophyletic, almost invariably in the context of crustaceans and hexapods together forming a monophyletic group (see discussion of Tetraconata below). Paraphyly of Crustacea relative to Hexapoda is a recurring theme, but precisely which group(s) of Crustacea is sister to Hexapoda differs between analyses, as do most of the major groupings between well-established crustacean clades. Candidates for the sister group of Hexapoda are Branchiopoda (references cited above), Copepoda or Branchiopoda, based on nuclear ribosomal genes (Mallatt et al., 2004, Mallatt and Giribet, 2006, von Reumont et al., 2009), and a clade of Remipedia and Cephalocarida (using nuclear coding genes; Regier et al., 2008, fig. 3). Crustacean relationships in Fig. 2 follow the summary diagram of Regier et al. (2008), depicting a clade that unites malacostracans and branchiopods together with some ‘‘maxillopodans’’(copepods and thecostracans), remipedes and cephalocarids as the closest relatives of hexapods. Crustacean paraphyly results from the exclusion of ostracodes and ichthyostracans (branchiurans and pentastomids; Møller et al., 2008) from this group.