I found that too but it is a good way to have a lot of answers about the fish. As we may see here using a picture to identify a fish is not a good idea. Fish siting on a flat ground looking much different than fish sitting on a wave shaped wood.
Copy/Paste
Parancistrus can be characterized by the presence of a membranous connection between the dorsal and adipose fins, cephalic and body scutes not carinate and a large gill opening. Armbruster (1997) additionally diagnosed the genus based on posterior deflection of the hyomandibula and presence of fleshy folds along the dorsal-fin base of nuptial males. Parancistrus can be further distinguished from Ancistrus and Chaetostoma by having a plated snout and from all other genera of the Ancistrini (sensu Armbruster, 2004), except Baryancistrus, Oligancistrus, and Spectracanthicus, by the connection between dorsal and adipose fins; from Baryancistrus, Oligancistrus, and Spectracanthicus, by the large gill openings.
Here are a few pictures of preserved specimens.
Gill openings large
Gill openings restricted to compare with (Preserved Baryancistrus sp.)
Steep forehead, flat forehead, snout etc, well mystery fish compare with Baryancistrus.
And on the end do not forget that it is just a young fish, far away from it's final shape and everything here is just a quick inspection.