Plot the circle.
Now use line() to draw the armature, using a higher LineWidth and a Marker of 's' (square) and a MarkerFaceColor of 'r' (red), possibly using a MarkerEdgeColor of 'k' (black). Store the handle of this line().
Then, at each step of the animation, set() the line XData and YData properties to reflect the new line position. Then call drawnow() to make the updated line show up.