Pankovaia semitubulata gen. et sp. n. (Microsporidia: Tuzetiidae) from nymphs of mayflies Cloeon dipterum L. (Insecta: Ephemeroptera) in Western Siberia.

The ultrastructure of a new microsporidian, Pankovaia semitubulata gen. et sp. n. (Microsporidia: Tuzetiidae), from the fat body of Cloeon dipterum (L.) (Ephemeroptera: Baetidae) is described. The species is monokaryotic throughout the life cycle, developing in direct contact with the host cell cytoplasm. Sporogonial plasmodium divides into 2-8 sporoblasts. Each sporoblast, then spore, is enclosed in an individual sporophorous vesicle. Fixed and stained spores of the type species P. semitubulata are 3.4 x 1.9microm in size. The polaroplast is bipartite (lamellar and vesicular). The polar filament is isofilar, possessing 6 coils in one row. The following features distinguish the genus Pankovaia from other monokaryotic genera of Tuzetiidae: (a) exospore is composed of multiple irregularly laid tubules with a lengthwise opening, referred to as "semitubules"; (b) episporontal space of sporophorous vesicle (SPV) is devoid of secretory formations; (c) SPV envelope is represented by a thin fragile membrane.