Boy, this is a hard one, in my opinion. It looks like haddoni, but to be happily attached on a rock, doesn't sound at all like a haddoni. Furthermore, to have been in a tank for at least 5 years and only be that size also doesn't seem very haddoni-esque. Haddonies usually have a reddish colored mouth. Noticeably different color compared to the surrounding oral disk. It's not gigantea because it doesn't have the noticeable verrucae. I suppose I would say haddoni at this point, but with some reservations.