Create the same object manually in Rhino and compare it to your baked version from Grasshopper. It looks like a normal NURBS seam that you can usually just ignore and won't bother an IGES export. Compare it also to what you see if you create a simple NURBS sphere in both Rhino and baked from Grasshopper. Such seams are for everyday purposes just a mathematical formality of how Rhino creates single surfaces into domes, spheres or a torus as a single untrimmed point editable surface. If you really want no seam, you'd have to drape a rectangle over it and trim the edges.