Pseudancistrus can be separated from the Neopleostominae, Hemipsilichthys, and
most of the Hypoptopomatinae by having a V-shaped dorsal-fin spinelet (vs. dorsal-fin
spinelet rectangular or absent); from all of the Hyopotopomatinae by lacking odontodes on
the ventral surface of the pectoral girdle; from the Loricariinae by having four or five rows
of plates on the caudal peduncle (vs. three) and by having an adipose fin; and from Delturus and Hemipsilichthys (a new subfamily; Armbruster 2004) by having a single (rarely
two) median, preadipose plates (vs. three or more).