Electron microscopy of negative-stained splayed or sectioned flagella. Doublets of the typical well-defined T-shaped RS with a compact spokehead and a thin stalk vertical to outer doublets (A) or less typical spokes (B) identified in wild-type samples. In RSP16⁻ flagella, the doublets of spoke-like images were present but the head region appeared less defined and the stalks tilted more frequently (C–E). (F) Cross sections showed wild-type RS with a bulbous spokehead abutted against CP and a long stalk associated to outer doublets (top). The RSP16⁻ RS appeared less homogenous. A few spokes in each section often appeared with a Y, J, or stunted T shape with a shorter stalk and a deformed head farther away from the CP apparatus (arrowheads).