Light and electron microscopic cytology of Trichotuzetia guttata gen. et. sp. n. (Microspora, Tuzetiidae), a microsporidian parasite of Cyclops vicinusUljanin, 1875 (Crustacea, Copepoda)

The microsporidium Trichotuzetia guttata gen. et sp. n., a parasite of the copepod Cyclops vicinus in the Czech Republic, is described based on light microscopic and ultrastructural characteristics. All life cycle stages have isolated nuclei. In the merogonial reproduction multinucleate plasmodia divide by plasmotomy, yielding uninucleate merozoites. Sporonts develop into multinucleate plasmodia, which split in a rosette-like manner, initially into wide lobes with large nuclei, finally into narrow lobes with small nuclei. Sporoblasts are formed in individual sporophorous vesicles generated by the sporogonial plasmodium. Immature sporogonial stages are covered by fibrillar projections uniting the exospore with the envelope of the sporophorous vesicle. Mature spores, which are pyriform with pointed anterior end, normally lack projections. Unfixed spores measure 4.6-5.7x2.7-3.3 µm. The exospore is four-layered. The anterior lamellae of the polaroplast are wide. The posterior ones (present in a short zone) are narrow close to the filament, wider at the periphery. The polar filament is isofilar with 9-10, 102-131 nm wide, coils in a single layer close to the spore wall in posterior half of the spore. The angle of tilt is 60-65°. Isometric, 21-25 nm wide virus-like particles were observed in the nuclei of mature spores. Experimental transmission of the microsporidium per os has failed. The small subunit rRNA gene has been sequenced and the data have been used in a phylogenetic analysis (PAUP). The species is compared to previously described microsporida of copepods, and the taxonomy is discussed.