Figure 11. Comparison of archigregarine (A–B) and eugregarine (C–F) cell organization with their main diagnostic characteristics (candidate synapomorphies).

(A and C) Cross sections of the cortex of a typical representatives showing regularly arranged longitudinal subpellicular microtubules (smt) in archigregarine longitudinal folds vs. ripple dense structures (apical arcs (aa)) and 12-nm filaments (apical filaments (af)) closely adjacent to the inner membrane complex (imc) of the pellicle within the tops of eugregarine epicytic crests; typically, internal lamina (il) forms links in the bases of the epicytic crests; pm, plasma membrane. (B) Archigregarine trophozoite showing a mucron (mu) with an apical complex (conoid (co) and rhoptries (rh)) and mucronal food vacuole (mv) performing myzocytosis (the cell junction type between the host and parasite cells is septate junction); the cytoplasm is rich in microneme-like organelles (mo). (D) Formation of the epimerite (ep) in eugregarines: a protuberance of the gregarine cell emerging ahead of the degrading apical complex. (E) Epimerite (so-called “mucron”) of some aseptate gregarines Lecudina spp. without the apical complex and with a large flat frontal vacuole and microtubules in the base. (F) Epimerite of septate gregarines with the same structures and with mitochondria. In eugregarines, the cell junction between the host and parasite is formed by two closely adjacent plasma membranes and there is no myzocytosis (or perhaps only in the earliest developmental stages before the reduction of the apical complex).