Light and electron microscopic study of Agglomerata volgensae n. sp (Microspora: Dubosqiidae), a new microsporidian parasite of Daphnia magna (Crustacea: Daphniidae)

The new microsporidium Agglomerata volgensae n. sp. is described based on light microscopic and ultrastructural characteristics. The parasite invades the hypoderm and adipose tissue of Daphnia magna and causes hypertrophy. All life cycle stages have isolated nuclei. Sporogonial plasmodia divide by rosette-like division, producing 4-16, usually 8, sporoblasts. A sporophorous vesicle is initiated after the first nuclear division of the sporont. The fragile vesicle either collects all daughter cells of the sporont, or the vesicle divides together with the plasmodium to enclose spores in individual sporophorous vesicles. Fibril-like projections connect the exospore with the envelope of the sporophorous vesicle. Tubules, with walls of exospore material, are formed together with the sporoblasts. Mature spores are pyriform with pointed anterior pole and an obliquely positioned posterior vacuole. Unfixed spores measure 3.2-3.7x1.7-2.0 mu m. The exospore is layered, approximately 38 nm thick. The polar filament is lightly anisofilar with 2-3 wide anterior coils, and 2-3 more narrow posterior coils, in a single layer of coils in the posterior half of the spore. The polaroplast has two regions: irregular wide lamellae or chambers surrounding the straight part of the filament, and more loosely arranged narrow lamellae in the coil region. The discrimination from other microsporidian species and the systematic position are briefly discussed.