Unrooted ML tree for dxs (log likelihood= −35,861.100656) constructed using Phyml with WAG substitution matrix, based on a matrix comprising 55 OTUs and 497 sites. OTU names in sans serif indicate they are eukaryotic orthologs, and the bold arrow denotes the Perkinsus marinus ortholog. Haptophyta OTU is a synthetic sequence composed of Emiliania, Isochrysis, and Pavlova ESTs (supplementary table S3, Supplementary Material online) and lacks 23% of sites. Heterocapsa OTU is also a synthetic sequence derived from ESTs and lacks 6% of sites. Cyanobacterial (Cya) and alpha-proteobacterial (α-Pro) orthologs are indicated. Numbers adjacent to the nodes indicate bootstrap support (100 replicates), and values below 50% have been omitted. The scale bar indicates the number of substitutions per site.