I tell you, the navel issue has been baking my noodle for a few years now, but I am of the notion that our hero would possess an ompholic dent that would pass enough as a navel. With the often more rudimentary delivery of babies in the Half-Continent I am thinking that there would be such a variety of quality of "belly-buttons" that Rossamünd's little dent would not look too out of place.
As to theroid (or therian or theraphim) for monster but teratologist for monster-hunter (thank you, master portals):
~ "thera" and "teratos" are both Attic words for monster, so it is simply the use of different root words that accounts for this variation. More-over, it is common in both Attic and the English language (and therefore Brandenard too) that "t" and "th"are exchanged with each other in the development of a word, especially "th" being shortened to "t".
How's that for some answers?
BTW, ompholascepsis means "navel-gazing".