Development, ultracytology and taxonomical position of Thelohania corethrae Schuberg and Rodriguez, 1915 (Microspora, Thelohaniidae)

Abstract

The development and ultracytology of a microsporidium identified as Thelohania corethrae are briefly described. The development conforms with the characteristics of Thelohaniidae: 8 diplokaryotic merozoites are formed by rosette-like budding, the diplokaryotic sporont divides meiotically and gives rise to a sporogonial plasmodium with 8 isolated nuclei, and 8 sporoblasts are formed. The uninucleate spores are nearly oval in fresh preparations, pyriform in stained smears. The envelope of the sporophorous vesicle is subpersistent and mature spores are rarely seen in groups of 8. The exospore has the layered construction typical for the Thelohania -like microsporidia, the polaroplast is lamellar with narrow anterior and wide posterior lamellae, and the polar filament is anisofilar. The species is variable, especially concerning the persistence of the sporophorous vesicle, the occurrence of macrospores, and the ratio wide to narrow coils of the polar filament. In the characteristic lesions formed by the microsporidium the external part is devoid of microsporidia, and mitochondria are prominently aggregated externally to the microsporidia-filled zone. The characteristics used to discriminate between T. corethrae and Plistophora chaobori are found to lack diagnostic value and P. chaobori is considered to be a younger synonym of T. corethrae . The ultrastructural findings exclude T. corethrae from the genus Thelohania , and the new combination Systenostrema corethrae is proposed.