Two Tetrasporoblastic Microsporidian Parasites of Caddis Flies (Trichoptera) with Description of the New Species Episeptum invadens sp. n. and Episeptum circumscriptum sp. n. (Microspora, Gurleyidae)

Abstract

Summary The two microsporidia Episeptum invadens sp. n. and Episeptum circumscriptum sp. n. are described based on light microscopic and ultrastructural characteristics. All life cycle stages have isolated nuclei. The merogonial reproduction was revealed as plasmodia with a small number of nuclei and groups of merozoites. The sporogony yields four sporoblasts by rosette-like budding, enclosed in a sporophorous vesicle produced by the sporont. Spores are pyriform with pointed anterior pole. The exospore is plurilayered and the polar filament is lightly anisofilar. Unfixed spores of E. invadens measure 2.2–2.5×3.2–3.6 µm. The polar filament makes 5–7 coils, the 2–3 anterior coils are the widest (100–126 nm). The anterior polaroplast has wide lamellae, the posterior closely packed lamellae. The host is Limnephilus fuscicornis (fam. Limnephilidae). The fat body lobes are completely invaded by the parasite and there is a prominent lysis of the host cells. Unfixed spores of E. circumscriptum measure about 2.1×2.5–3.7 µm. The polar filament makes 4–5 coils, the 1–2 anterior are the widest (94–102 nm). The anterior region of the polaroplast has wide chambers, the posterior closely packed lamellae. The host is Hydropsyche siltalai (fam. Hydropsychidae). Infection is mostly restricted to the superficial layers of cells in the fat body lobes, and there is only slight lysis of infected cells. The taxonomic problems with the tetrasporoblastic microsporidia and the assignment to genus are briefly discussed.