Convert closed curve to segment in Segment Editor

I am trying to annotate (manually segment) 2D images, the closed-curve markup is of particular use. How can I convert the curve into a segment in Segment Editor? Apart from closed curve, is there a way to simply place/edit ellipse markups? It’s rare, but sometimes I am missing these simpler tools like closed curve/polygon/ellipse in the Segment Editor toolbar (even the SegmentEditorExtraEffects extension does not have those). Usually, these tools are too simplistic. But in my case, I am trying to segment iris/pupil in eye closeup images, and ellipses would be particularly useful.
Thanks in advance!

Polygon drawing is called “Draw” effect. For multiple slices you can use “Scissors” effect.

Circle and sphere drawing is available in “Paint” effect. Circle, sphere, and cylinder drawing is in “Scissors” effect (we could add ellipse here, too, but there hasn’t been significant demand).

You can draw/edit closed curves on multiple slices and convert to segment using “Surface Cut” effect (provided by SegmentEditorExtraEffects extension). You can draw open curves and convert them to segment using “Draw curve” effect (in SegmentEditorExtraEffects extension, too).