Hi Birger,
could very well be L 71/L 181/L 249.
It is difficult to see in the pic, but it seems that it has 8 soft fin rays in the dorsal which would rule out most of the other ancistrus.
Do you know how it looked like when it was smaller ?
Here you can find some more pictures to compare (additional to the ones here):
http://www.l-welse.com/reviewpost/showp ... roduct/195
Cheers,