Polar capsule

Polar capsules are structures found in the valves of Myxosporean parasites, which contain the polar filament. The polar capsule is constructed of a proteinaceous and a polysaccharide layer, both layers of which continue into the polar filament.
The mouth of the capsule is covered with a cap-like structure. This structure may function as a stopper, its digestion in the alimentary tract possibly triggering the discharge of the polar filaments.