Mitosis in the protostelidPlanoprotostelium aurantium

Summary Mitosis in the protostelidPlanoprotostelium aurantium Olive andStoianovich is characterized by an open, centric spindle. The nuclear envelope breaks down prior to metaphase, begins to reform during late anaphase, and is complete by telophase. Centrioles are present at the poles throughout mitosis and are devoid of rootlet microtubules from metaphase to late anaphase. Chromosomes are small and numerous and are attached to single kinetochore microtubules during metaphase and early anaphase. Chromosome separation takes place by a presumed shortening of the chromosome to pole spindle followed by a lengthening of the interzonal spindle. Mitosis inP. aurantium is similar to that of certain other protostelid amoebae and to myxomycete amoebae, but it is considerably different from that of dictyostelid amoebae. The phylogenetic significance of this is discussed.This research represents part of a Ph.D. dissertation presented to the University of North Carolina.