Ultrastructural study and description of Ordospora colligata gen, et sp. nov. (Microspora, Ordosporidae fam. nov.), a new microsporidian parasite of Daphnia magna (Crustacea, Cladocera)

The new microsporidium Ordospora colligata gen. et sp. n. is described with emphasis on the ultrastructural characteristics, The parasite, which is superficially similar to Glugoides intestinalis (Chatton, 1907), invades the gut epithelium of Daphnia magna, where the complete development takes place in a host cell-derived parasitophorous vacuole, Merogonial and sporogonial stages occur together in the vacuole, with presporal stages at the periphery, mature spores aggregated in the centre, All life cycle stages have isolated nuclei. Merogonial plasmodia are initially rounded, later elongated, and they give rise tit four merozoites. The bouts of merogony ale unknown. The sporont produces two sporoblast mother cells, which often remain coupled. Each cell generates a chain of four sporoblasts. Sporophorous vesicles are not produced. Mature spores are pyriform with a pointed anterior pole and with an obliquely positioned posterior vacuole. Unfixed spores measure 1.33-2.29 x 2.32-3.69 mu m. The exospore is uniform, about 11 nm thick. The polar filament is isofilar, 82-85 nm wide, making 5-6 coils in the posterior half of the spore, The polaroplast is uniform, composed of about 28 nm, wide lamellar components, where the lamellae are folded around each other, The discrimination from other microsporidian species and the systematic position are briefly discussed. A new family, Ordosporidae, is established and Endoreticulatus durforti Martinez et al., 1993 is transferred to Ordospora.