They certainly look like bristles, I would recomend you post a link to this in the catfish forum. There are lots of plecostomus pros in there and I'm sure they will confirm this..
I did a quick search and found out they have several L numbers (L104, L162, LDA22)
but also found out they are one of th plecos that can not survive without eating wood.
I'm sure you knew this and have plenty of wood for it to eat in your tank.
I have bog wood thats been in there over a year now. Length wise he's about two inches. I'll look into getting a little bit of drift wood if possible. He seems to be doing ok.