An update on the systematics of the phylum Ciliophora doflein, 1901: the implications of kinetid diversity.

Recent classifications of the phylum Ciliophora are compared with the system proposed by Small and Lynn in 1981 and revised in 1985. The classes COLPODEA, PHYLLOPHARYNGEA, OLIGOHYMENOPHOREA and NASSOPHOREA sensu Small & Lynn are considered monophyletic by a number of researchers. The classes LITOSTOMATEA and PROSTOMATEA sensu Small & Lynn are not as well accepted. Some divergence of opinion arises in recognition of the categories included in the classes KARYORELICTEA and SPIROTRICHEA sensu Small & Lynn, in which the great diversity of cortical ultrastructure is still not recognized in the taxonomy. Numerous minor groups, for example the phacodiniids, plagiopylids and schizocaryids, present taxonomic problems that may not be solved by ultrastructural examination. This is also true of the subphyletic divisions where there are substantial differences of opinion about relationships among the classes.