Summary
The structure of the polar filament of a species of Nosema (Protozoa, Microspora) invading a sea horse, Hippocampus erectus, has been studied with the electron microscope. Filaments extruded from spores were examined on ultrathin sections and on negatively stained preparations. The extruded filament appears as a hollow tube whose walls are composed of membranes; mostly there are three membranes separated or closely joint together. There was no positive evidence of fibrillar structures in the extruded filaments. In a resting spore, the membranous walls of the filament, although less distinct, are also discernible. A collar-like structure at the base of the filament provides for the anchorage of the extruded filament, being firmly wedged in the aperture pierced in the spores shell by the filament discharge. In resting state this structure attaches the basal part of the filament to the organelle known as polar cap. No evidence was found of a “terminal sac” at the loose end of the filament. During extrusion, sporoplasm passes through the cavity of the filament in an extremely elongated state. The empty space in the extruded spore shell is in fact the enlarged posterior vacuole. At the anterior end there is a separated space communicating with the filament cavity.
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Lom, J. On the structure of the extruded microsporidian polar filament. Z. Parasitenk. 38, 200–213 (1972). https://doi.org/10.1007/BF00329598
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DOI: https://doi.org/10.1007/BF00329598