Figure 10 in The search finds an end: the morphologically chimeric hysterocinetids belong to the subclass Hymenostomatia (Ciliophora: Oligohymenophorea)

Figure 10. Phylogenetic tree based on the nuclear 18S and mitochondrial 16S rRNA gene sequences, showing the phylogenetic position of hysterocinetids within the class Oligohymenophorea. Note that hysterocinetids are nested within the 'paravorax' clade of the genus Tetrahymena. The 'paravorax' clade, at the present state of knowledge, comprises both free-living (e.g. T. paravorax), as well as endosymbiotic ciliates associated with freshwater planarians (T. nigricans), bivalves (T. glochidiophila and T. unionis), and lumbricid earthworms (Hysterocineta bellerophon and Protoptychostomum simplex). Posterior probabilities for Bayesian inference conducted in MrBayes and bootstrap values for maximum likelihood conducted in IQ-Tree were mapped onto the 50%-majority rule Bayesian consensus tree. Fully statistically supported nodes are marked with red solid circles. The scale bar denotes one substitution per ten nucleotide positions.