On the cytology and development of Tuzetia schneideri (Léger and Hesse, 1910) Maurand, 1973 (Microspora, Tuzetiidae)

Abstract

The light- and electron-microscopic cytology, and the life cycle, of the microsporidium Tuzetia (Nosema) schneideri Léger and Hesse, 1910 are described, based on material isolated from the midgut of larvae of the mayfly Ephemera danica , collected from a locality in southern Sweden. All developmental stages have isolated nuclei. Merogonial stages are considerably greater than sporogonial stages. Daughter cells of both the merogonic and sporogonic reproduction are produced by rosette-like budding from a plasmodium with a small number of nuclei. Living spores are oval, 2.5-2.8 × 4.9-5.6 urn great. The spore wall is three-layered, with a uniform electron-dense exospore. The polaroplast has anterior tightly packed lamellae and posterior tubular or sac-like compartments. The isofilar polar filament is arranged in 7-9 coils in the median third of the spore. The sporophorous vesicle is initiated, in the sporont stage, as blister-like protrusions of electron-dense material. During the maturation from sporoblast to spore the vesicle primordia unite to a continuous envelope. Mature spores are enclosed in individual sporophorous vesicles with a c. 17 nm thick, uniform envelope, and with 32-43 nm wide tubules traversing the episporontal space. Problems with the identification and nomenclature are discussed.