The fine structure of Nosema sp. Sprague, 1965 (Microsporida, Nosematidae) with particular reference to stages in sporogony

Abstract

Stages of Nosema sp. occurring in the skeletal muscle of an experimentally infected crab, Callinectes sapidus, were observed by means of electron microscopy. Only diplokarya and stages in sporogony from sporoblasts to spores were seen. All these were extracellular. The fine structure was basically similar to that which has been reported for other Microsporida but there were some peculiar features. Chief of these were a new kind of polaroplast and a large cavity or “cavum” in which it was suspended. The polaroplast, a bipartite structure, had a compactly laminated anterior portion. This part had been seen in a previous study as a chromophilic body which, suspended in the cavum, resembled a coiled polar filament in a capsule. Another peculiarity was the presence of numerous short bristles emanating from the surfaces of the sporoblasts and spores. An inference that the zygote in Nosema gives rise to two sporoblasts suggests the need for reexamination of the definition of the genus and of some commonly used terms.