Two separate pieces on either side of the glass wing. The two pieces unscrew form each other. I can't remember if there is a small phillips head screw in the outside piece or if the entire outside piece unscrews.
There was another thread regarding the vent closures and Taylor Marine in Delaware had OEM replacements at $40+ plus shipping - I think total for one was a little over $50. Someone else posted a Chinese knockoff for about $10. I did a search on Amazon Prime and bought four of the knockoffs. Problem with the knockoffs is that the mounting holes don't line up properly. I had to take new units apart & then grind the ribs down with a Dremel to get it to work with the original mounting bracket