Maximum likelihood tree of the GPx homologs. The analysis was conducted on the alignment of amino acid sequences with TREE_PUZZLE. Gaps in the alignment were removed in a pair-wise manner as missing information. The plant PHGPxs [GenBank: CAC17628, NP_191867, NP_566128], which showed the long branches, were taken as the outgroup. The identity of each sequence was provided by a protein identification number followed by the name of donor specie. The platyhelminth genes are presented in the boldface letters and those retrieved from EST databases are marked with the italicized accession numbers of mRNA sequences. The entries with a codon for selenocysteine (Sec) and concurrent Sec insertion sequence within the corresponding mRNA sequences are indicated by ‡. The symbol § marks the proteins with the Cys motif. Quartet support values are presented at each of the major branching points.