Figure 6 in A revised taxonomy and phylogeny of opalinids (Stramenopiles: Opalinata) inferred from the analysis of complete nuclear ribosomal DNA genes

Figure 6. Cladogram showing the evolution of Opalinata* based on the proposed evolution of morphological traits (white circles; Delvinquier and Patterson 1993) and the characteristics of the rRNA genes (green circles). The relationships within Proteromonadida are not clear and are represented as a polytomy. Evolutionary steps are as follows. (1) Uninucleated cells develop cytoplasmic membranes with ridges or folds supported by a cortical cytoskeleton; few flagella* with a transitional helix in its structure; rRNA with secondary structure and GC content similar to that of outgroup taxons (i.e. Blastocystis). (2) Multiple flagella covering the cell surface; marginal falx. (3) Insertions made of short tandem repeats (STRs) in the expansion regions of rRNA; low GC in rRNA insertions and ITS1–ITS2 regions. (4) Binucleated (occasionally four-nucleated) cells. (5) Increase in number and length of rRNA insertions; very low GC content in rRNA insertions and ITS1–ITS2 regions. (6) Axial falx. (7) Multinucleate cells. (8) Partial loss of kineties. The position of Hegneriella* if valid* cannot be determined with available data.