Problems in the development of an explicit hypothetical phylogeny of the lower eukaryotes.

A semi-explicit arrangement of the lower eukaryotes is provided to serve as a basis for phyletic discussions. No single character is used to determine the position of all the groups. The tree provides no ready separation of protozoa, algae and fungi, groups assigned to these traditional assemblages being considered to be for the most part inextricably interwoven. Photosynthetic forms, whose relationships seem to be more readily discernable, are considered to have given rise repeatedly to nonphotosynthetic forms. The assumption that there are primitive "preflagellar" eukaryotes (red algae, non-flagellated fungi) is adopted. The potential value of mitochondrial features as indicators of broad affinities is emphasised, particularly in determining the probable affinities of non-photosynthetic forms, and this criterion is contra-indicative of a ciliate ancestry for the Metazoa. In the arrangement provided the distributions of chloroplast, mitochondrial and flagellar features match one another well, suggesting their probable co-evolution.