Ultrastructure of the microgamont and microgamete of Eimeria funduli, a coccidium parasitizing killifishes

Abstract. The ultrastructure of the microgamont and microgamete of the coccidium Eimerici funduli was studied in hepatocytes of the killifish Fundulus grandis and F. similis . During microgametogenesis, the nuclear chromatin condensed, marginated, then differentiated into a peripheral dense portion that became the nucleus of the microgamete and a central clear portion that remained in the gamont. Near each nucleus was a mitochondrion and four microtubules which were incorporated into the microgamete. In microgamonts, dense polysaccharide granules (50–60 nm diameter) were demonstrated with the periodic acid-thiocarbohydrazide-silver proteinate method. Flagella extended into the parasitophorous vacuole from basal bodies situated near nuclei. Microgametes budded from the surface of the microgamonts. The microgamete consisted of a nucleus, two flagella and basal bodies, a mitochondrion, a rudimentary basal body, four microlubules, a perforatorium, and a dense rod-like structure. The elongate nucleus was narrow anteriorly and bulb-like posteriorly. One of the flagella was attached to the body of the microgamete. A mitochondrion that was swollen anteriorly and constricted posteriorly ran alongside the nucleus. The four microtubules appeared to arise from a rudimentary basal body and were closely related to the mitochondrion. Two of them extended nearly the length of the nucleus. The rod-like structure appeared to develop from a thickening of the limiting membrane of the microgamont. Fertilization was not directly observed, but microgametes were found in the parasitophorous vacuoles of several macrogamonts.