As far as I know all ancistrus species have 9 rays. Ancistrus dolichopterus is L183 (starlight bristlenose) and it also have 9 dorsal ray. If we are being honest, most common bristlenose are crosses of Ancistrus triradiatus, Ancistrus pirareta, and a number of other strains because all ancistrus can cross breed and people were not as good at identifying the different strains when they were first imported.
To address cjayBetta's original question though, what you have is a sailfin pleco. It will get huge, it will poop a lot, and as it gets older it may become very aggressive (or not) I personally would not keep a Sailfin with a Betta. Bettas are notorious over eaters, as you have experienced, and there may be aggression issues later on.
edit: plecos should be fed every day. If feeding algae wafers is making your betta fat try feeding fresh veggies like zuchinni. The pleco will love it and the betta will not eat much if any.