Further observations on the ultrastructure of Cystosporogenes operophterae (Canning, 1960) (phylum Microsporidia) parasitic in Operophtera brumata L. (Lepidoptera, Geometridae).

Reinvestigation of Cystosporogenes operophterae [J. Parasitol. 46 (1960) 755] by electron microscopy confirmed that development in host cells takes place in a vacuole with a single membrane at its boundary. Although ribosomes were not clustered on this membrane, it is hypothesised that it originates from host endoplasmic reticulum. The dome-shaped anchoring disc, the morphology of the polaroplast and the separation of the polar tube coils from the ribosome-packed cytoplasm are newly described details of spore structure. The polaroplast consists of an outer region of compact lamellae forming 'arms' surrounding an inner region of widely spaced lamellae. The 'arms' extends back into the region of an elongate nucleus. The genera Cystosporogenes and Endoreticulatus were differentiated by their positions in a previously obtained 16S rDNA phylogeny and on the new ultrastructural data.