Maximum Likelihood phylogenetic tree of the class Plagiopylea based on 18S rRNA gene sequences (unmodified character matrix, see test). The GTR + I + G model of substitution (with the continuous gamma function approximated by four discrete categories) was employed. 92.4% of 100,000 randomly chosen quartets had well-defined topologies. Average base frequencies calculated by TREE-PUZZLE were 28.3% (A), 18.5% (C), 26.0% (G), 27.2% (T); no sequence deviated from these values (p>> 0.05). The numbers associated to each node represent bootstrap values and posterior probability, respectively (values below 60/0.75 are not shown). The bar stands for an estimated sequence divergence of 10%.