The fine structure of reptilian Isospora species with intranuclear endogenous development.

The fine structure of the endogenous stages of five species of Isospora of lacertile hosts is reviewed and compared. All species were intranuclear and were the following: I. deserti, from Agama pallida from Israel; I. cannoni, from Diporiphora australis from Queensland, Australia; and new, yet undescribed species from Hemidactylus turcicus from Israel. Heteronota binoei from Queensland, and Carlia rhomboidalis from Queensland. In young infections the intranuclear parasitophorous vacuole (PV) maintained at one point a junction zone with the nucleolemma. Finding couples of trophozoites sharing the same PV suggests a binary division (or endodyogeny?) prior to merogony. There was some overall conformity in structure among the respective stages of the different species, particularly of the gamonts. Some interspecific differences were, however, evident in the texture of the wall-forming bodies. The wall formation followed the scheme described for avian and mammalian eimeriid coccidia. The smaller size Isospora from C. rhomboidalis exhibited fine structural peculiarities and affected its host nucleus differently. More conspicuous peculiarities were evident in the differentiation process of I. cannoni meronts, involving a formation of centrally positioned large inclusions, a mitochondrial plaque-like organelle and large uniquely structured vesicular mitochondria.