Yes the little trapezoidal shaped thingy on the lens is a cam which mates with, and is pushed by, the little tear-dropped shaped cam just below (left hand side) of the camera when the shutter is depressed. The cam on the lens then rotates a shaft which is linked to the iris activation mechanism inside the lens. The whole system actually works pretty smoothly in practice.
The small pin beneath the lens mount on the camera locks the lens in place rotationally by mating to the little notched-out piece seen protruding form the back of the lens. This pin motion can be actuated by the shorter cylindrical button seen below the lens mount on the camera. Depressing this button pulls the pin out of the slot and is necessary to remove the lens.