Hello, Bill,
even though I am surely not the most qualified person to answer your question, I will try to give you a first answer by translating the P. nagyi-part of the new paro-book by Finke and Hallmann. I hope the authors will excuse possible ups and downs of my translation ……… :unsure:
Especially the forms of [i]P. nagyi from southern localities show a curiosity: The rim of the caudal is not pigmented but transparent. In the local forms from Kuantan and Pekan Nenasi the turquoise seam of the caudal fin is not located at the fringe of the caudal – which is different from all other species. Males in nuptial colouration seem to pretend to have shorter fins – an alleged contradiction to the accentuation of size and brightness of fins in paros.
So, we know two differentiable varieties : First, P. nagyi „Kuantan“, P. nagyi „Pekan Nenasi“ and further localities south of the terra typica, with white bands in the caudal fin and a prominent spot at the hind base of the dorsal fin.
Second, P. nagyi „Cherating“ with regular turquoise bands in all unpaired fins. The transparent fin margins/projecting fin rays, respectively, are, by far, not as distinctive as in the other forms. Thus, the caudal seems to be larger in P. nagyi „Cherating“.[/i]
Maybe this can be a first step to explain the form “Pekan Nenasi”.
Here the transparent margin of the caudal in “Pekan Nenasi” is very well to be seen: