Ultrastructural Study and Redescription of Coccospora micrococcus(Léger & Hesse, 1921) Kudo, 1925 (Microspora, Thelohaniidae), a Parasite of Midge Larvae of the Genus Arctopelopia sp. (Diptera, Chironomidae) in Sweden

Abstract

Summary The cytology of the microsporidium Coccospora micrococcus , which is a parasiteof the adipose tissue of midge larvae, Arctopelopia sp. , in Sweden, is described based on observations using light and electron microscopy. Merogonial plasmodia divide by plasmotomy and by rosette-like budding, yielding diplokaryotic merozoites. The number of merogonial cycles is unKnown. The sporogony probably begins with a meiotic division. Each diplokaryotic sporont yields eight sporoblasts. A fragile sporophorous vesicle encloses each group of spores. The monokaryotic spores are spherical. Living spores measure 2.5-2.7μm, fixed and stained spores 1.6-1.8 μm. The spore wall has a layered exospore with a double-layer. The polaroplast consists of an anterior lamellar and a posterior sac-like part. The isofilar polar filament is short, without coils. The membranes of the vacuole, produced by the Golgi apparatus, and their connection with the polar filament are visible in mature spores. There are two types of inclusions of the sporophorous vesicle: granular, initiated in the early phase of the sporogony, and tubular of exospore origin. The microsporidium is compared to the microsporidia with spherical spores, and the possible relations to the genus Pilosporella and to other Thelohania -like microsporidia are discussed.