Light microscope images of Protoopalina pingi Nie, 1935. (A) Living specimens, showing the normal trophozoites of P. pingi. Scale bar = 20 μm. (B) Living specimens, showing the flagella covering the body (arrowhead). Scale bar = 5 μm. (C) Specimens stained with Protargol, showing the somatic kineties and the nuclei with distributed nucleoli. Scale bar = 10 μm. (D) Specimens stained with Protargol, showing the somatic kineties in the posterior extremity (arrowhead). Scale bar = 5 μm. (E) Specimens stained with Protargol, showing the falx region in the anterior extremity (arrowhead). Scale bar = 5 μm. (F) Specimens stained with Heidenhain’s haematoxylin, showing the nuclei (arrow) and the corpuscles of uneven size (arrowhead). Scale bar = 20 μm.