there are I think between 25 and 30 different bristlenose/Ancistrus species. the potential size of most of these usually runs between 4" and 10", though there are not many species that grow past 8". there is definitely one called the "giant brisltenose pleco" that is supposed to get between 10-12" so I'd assume that's the one you had. most common bristlenoses however won't get that large.