Polar capsule
![Alataspora solomoni, a myxosporean parasite of Atlantic Horse Mackerel, showing the arrangement of the polar capsules on either side of the sutural line.](/Images/godic/202502/03/Myxobolus_spinacurvatura2943.jpg")
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.