Guyanancistrus is not likely to be a monophyletic entity. Although only Pseudancistrus brevispinis has been examined osteologically, the species attributed to Guyanancistrus
vary from P. brevispinis that lacks hypertrophied odontodes along the snout and that has
fully evertible cheek plates to P. niger that develops at least small hypertrophied odontodes
on the snout and that has the cheek plates very weakly evertible. No characteristics were
given to diagnose the genus or separate it from any genus other than Lasiancistrus in the
original description (Isbrücker et al. 2001). Lasiancistrus is a very well diagnosed genus
that is not particularly closely related to Pseudancistrus (Armbruster 2004). Lasiancistrus
is readily identifiable from Pseudancistrus by having whiskerlike odontodes among the
hypertrophied cheek odontodes and three rows of plates on the caudal peduncle (vs. 4–5 in
Pseudancistrus; Armbruster 2004)