Tardivesicula duplicata gen. et sp. nov. (microspora, duboscqiidae), a microsporidian parasite of the caddis fly Limnephilus centralis (trichoptera, limnephilidae) in Sweden

Abstract

The microsporidium Tardivesicula duplicata gen. et sp. nov., a parasite of the adipose tissue of larvae of the caddis fly Limnephilus centralis in Sweden, is described based on light microscopic and ultrastructural characteristics. All life cycle stages have isolated nuclei. The sporogony is polysporoblastic, yielding 16-32 spores. The spores are rod-shaped, 1.3-1.4 × 3.7-4.2 μm in living condition. The spore wall has a 34-40 nm thick, layered exospore, with a median layer resembling a unit membrane. The endospore is thicker than the exospore. The polaroplast has two lamellar parts, where the posterior lamellae are the widest. The isofilar, 128-149 nm thick polar filament is arranged in 9-10 coils in a single layer close to the spore wall in the posterior 2/3 of the spore. The angle of tilt is c. 45°. The transversely sectioned polar filament has distinct concentrical layers of variable thickness and electron density. Sporophorous vesicles are ellipsoid and fragile. The thin electron-dense envelope is initiated as narrow tubulus-like promordia, appearing when the nucleus of the sporont has divided once. The episporontal space of vesicles with sporogonial plasmodia is devoid of inclusions. Vesicles with sporoblasts and spores have tubular exospore-derived inclusions of two dimensions. The new genus is compared to genera with polysporoblastic sporogony in sporophorous vesicles, primarily to Cystosporogenes and Flabelliforma. The placing of the new genus in the family Duboscqiidae is discussed.