You can also create shapes with arcs of spirals.

When you click on the shape below you will be able to edit the parameters for one of the arcs on the right. Also you can drag the currently selected arc by it's origin point. Once again the polar coordinate grid moves with the origin.

There are two spiral arcs that create the shape. Each time you click on the shape, the arc that is editable will change. If you make the amount to "Add" = 0, you will get a circular arc like the ones you created before.