6 membered ring structure of monosaccharides are known as:
The ring structures of monosaccharides are similar to the ring structures of either pyran (a six-membered ring) or furan (a five-membered ring). For glucose in solution, more than 99% is in the pyranose form. Ref: Harper 28th edition, chapter 14.
Pyran
Furan
Aldose
Ketose