Figure 3.

Principal component analysis (PCA) of amino acid frequencies on the ribosomal protein dataset. The first three letters of each taxon name are plotted onto the principal axis. Note the position of the chaetognaths (Cha), in red. The most divergent sequences, furthest from the center, are those of priapulids, homoscleromorphs, tardigrades, platyhelminthes and nematodes. Homoscleromorpha is the only taxon to fail the chi-square test of divergence from overall composition (Additional file 3).