So "ap" means son of and "merch" means daughter of in the Welsh language, and I'm pretty sure it's the same for naming conventions. I don't think it changes after marriage. So, Rhiannon merch Sion is Rhiannon, daughter of Sion, and Sion ap Llywellyn is Sion, son of Llywellyn.
Humphreys, apparently, is both Welsh and English, and it comes from the given name Humphrey.
"That cynicism you refer to I acquired the day I discovered I was different from little boys."