Ultrastructural features of the gametogenic and sporogonic development of

Stages of gametogony and sporogony of the haemogregarine Hepatozoon sipedon, an apicomplexan parasite of the Northern water snake, Nerodia sipedon sipedon, were studied in the mosquito, Culex pipiens, by electron microscopy. Four days after mosquitoes fed on an infected snake, microgamonts and macrogamonts were observed in syzygy in parasitophorous vacuoles within fat body cells of the haemocoel. During microgametogenesis, two biflagellated microgametes were formed, one of which fertilized the macrogamete. After fertilization, zygotes increased rapidly in size, accumulating reserve material in the form of lipid inclusions. Beginning at 16 days post-feeding (PF), the nucleus of the immature oocyst underwent multiple divisions in the first stage of sporoblast formation. Small crystalloid bodies initially appeared in the cytoplasm of the dividing oocyst at 20 days PF. At 24 days PF, the oocyst contained hundreds of sporoblasts, each of which matured as early as 28 days PF into thick-walled sporocysts containing eight sporozoites and a large residual body. Sporozoites contained a large crystalloid body comprised of tightly-packed particles assembled in a paracrystalline array. The use of ultrastructural characters in the differentiation of Hepatozoon species is discussed in context with the current phylogenetic hypotheses of adeleorin taxa