Polar filament

A polar filament is a structure found in the polar capsule of myxosporean organisms, and is analogous to the "penetrant" structure found in cnidocytes.

The polar filament is coiled along the inner wall of the polar capsule, and is capable of rapid extrusion, during which it everts "inside-out". When everted, it is sticky, and probably serves to hold the spore on to the intestinal wall of the prospective host, and to help separate the valves of the spore.