Monophyly is essential prerequisite for species delimitation. In protists, molecular phylogenetic <br />
studies revealed, in recent years, many polyphyletic groups at all taxonomic levels, which afterwards led <br />
to their revisions for getting closer to natural classification. Above all, species-level polyphyly not only <br />
causes revisions of species, but also forces taxonomists to face species problems, especially species <br />
delimitation. <br />
Technological advancement in molecular biology represented by next-generation sequencing <br />
enables to develop various new methods for species delimitation, which open up a new way of <br />
taxonomy. Morphologically indistinct groups such as small flagellates or amoebas have been out of <br />
search for intraspecific polyphyly because of inability of delimiting their species boundaries. However, a <br />
new approach called &quot;reverse taxonomy&quot; including increased taxon sampling shed light on their species <br />
delimitation.