Neighbor-joining tree of cluster 3, which contains the D and H surface antigens. The known genes for P. primaurelia (156D, 156D beta, the putative 156H) are spiked into the alignment to identify the orthologs in the P. primaurelia AZ9-3 strain. The identified proteins that correspond to known SAgs in P. tetraurelia are indicated (51D, 51J, 51D gamma1, 51D gamma2, 51H alpha, and 51H beta). P. primaurelia is colored in yellow, P. biaurelia in pink, P. tetraurelia in blue, P. sexaurelia in red, and P. caudatum in black. Scale bar represents substitutions per site; branch label indicates percentage consensus support of 100 pseudoreplicates.