Scanning electron microscope images of Protoopalina pingi Nie, 1935. (A) Overview of P. pingi, showing many fused flagella over the body. Scale bar = 20 μm. (B) Anterior end of P. pingi, showing the densely flagellated body surface. Scale bar = 5 μm. (C) Caudal tip of P. pingi, showing the flagella (arrowhead) in the region barren of flagella. Scale bar = 2.5 μm. (D) The flagella are arranged in the ridge, showing the proximal ends of the flagella (arrowhead) and ridge (r). Scale bar = 1.5 μm.