The flagellar apparatus of Mallomonas splendens (Synurophyceae) at interphase and its development during the cell cycle

The interphase configuration of the flagellar apparatus of Mallomonas splendens (G. S. West) Playfair displays several features that are novel in the Synurophyceae. One of the two basal bodies usually has no flagellum, and two fibrous bands connect the basal bodies. Surrounding the basal bodies is a distinctive, fibrous capsule which is continuous with a thick, fibrous band that constitutes the anterior portion of the rhizoplast. The remainder of the rhizoplast spreads over the nuclear apex as numerous, prominently striated straps. A single, three‐membered, mi‐crotubular root (R1) forms a loop at the cell anterior and then descends from the loop to abutt on the rhizoplast near the nuclear apex. The descending portion of R1 displays at least two orientations with respect to the basal bodies.

Two new basal bodies appear before mitosis and bear the rudiments of new Ills. At preprophase these new roots are 2–3 μm long, and new rhizoplasts, which organize (nucleate?) microtubules of the incipient mitotic spindle, arise from the proximal end of the new basal bodies. The latter produce new fiagella as the parental flagellum shortens. Simultaneous to these developments is the disassembly of the parental rhizoplast and the descending portion of the parental RI. At metaphase the two pairs of basal bodies have separated so that each pair consists of a parental and a daughter basal body. The parental R1 loop is absent and the new R1s form semi‐loops around each pair of basal bodies. The rhizoplasts extend down either side of the nuclear material as the spindle becomes fully formed. The new loops are completed at mid‐cytokinesis. At the end of cytokinesis the roots elongate towards the nuclear apex, and each rhizoplast takes on the interphase appearance. Mitosis in M. splendens is compared to that in the Chrysophyceae.