Flagellate Phylogeny: A Study in Conflicts*

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Abstract
SYNOPSIS.Information relating to the ultrastructure of 4 organellar systems of flagellates—nuclei (including mitosis), flagella, mitochondria and chloroplasts—is examined for bearing on the probable phylogeny of the principal flagellate groups, first considered singly and then in combination. The mitotic mechanism has not proved to be as conservative a character as might be hoped, but still remains characteristic for the average condition in many of the groups. Flagellar features are useful if allowance is made for the reduction or multiplication of the basic pair, and the loss of lateral and terminal hairs seems to have occurred independently several times. The presence of paraxial rods within flagella may be a useful indication of affinity. Rootlet systems are not dealt with in detail here, although the possible similarity between axial microtubular sheets in axostylar flagellates and some members of the green algae containing “manchettes” is noted. The basic patterns of chloroplast internal structure are summarized and their general agreement with other characters is affirmed, noting however that cryptomonads may be closer to the green flagellates (including euglenoids) than is generally accepted. Attention is drawn to the potential value of internal mitochondrial morphology as an indicator of large assemblages. Finally, a “tree” based on multiple cell organizational features is presented and discussed.