ofPolyline open Arc

I cannot seem to create an open arc using ofPolyline.

ofSetLineWidth(3.0f);
ofPoint point1(150,120);
curver.arc(point1,100,100,0,270,180);
curver.draw();

results in
Image may be NSFW.
Clik here to view.

I cannot use ofPath because I'm using the ofxShiva renderer (for smooth shapes) and it does not support arcs using ofPath yet.

I'm sure I'm missing something simply but I just can't find it.
Thanks,
Casey