polar tube GO:0044099 2009-06-09T03:12:32Z cellular_component A highly specialized structure unique to microsporidia that is required for host cell invasion. In the spore, the polar tube is connected at the anterior end, and then coils around the sporoplasm. Upon appropriate environmental stimulation, the polar tube rapidly discharges out of the spore, pierces a cell membrane and serves as a conduit for sporoplasm passage into the new host cell. jl cellular anatomical structure