How do I remove the webbing/ starlacc pit from the mesh after subdividing..
Actually you've filled the bottom and top edges with a simple F (fill), but as the shape is round it goes bad because the center of the whole face is out of this semi-circular shape. So you should keep quads:
- Select those faces and press X (delete) > Faces.
- Now select all these vertices except the extreme right and left ones.
- Press W > Bridge Edge Loops. It will fill the gap between the edges.
- Then finish the process, select the extreme right vertices and press F. Same for the extreme left vertices.
- Do the exact same process for the opposite edge.