Hopliancistrus is a genus of armored suckermouth catfishes (Loricariidae) endemic to Brazil, part of the Ancistrini tribe that produces most of the bristlenose-type plecos in the trade. The atlas covers 5 species, all restricted to Brazilian river drainages, ranging roughly 4.5–6 in as adults. The genus name reflects hook-like, evertible odontode plates around the head and cheeks, a trait shared with several rheophilic Ancistrini that live wedged among boulders and cobble in fast, well-oxygenated stretches of Amazon tributaries, where they graze biofilm and algae from rock surfaces and take some invertebrate matter as well.
Two species in the atlas, Hopliancistrus tricornis and Hopliancistrus xikrin, circulate in the hobby under their L-number codes, L212 and L171, and are prized by specialist pleco keepers for their bold pattern and compact size relative to many other Loricariidae. Fish of this genus need strong current, high dissolved oxygen, and driftwood or rock cover, mirroring the rapids habitat they come from. With one species assessed as Endangered and two already flagged for CARES conservation breeding, the genus illustrates a pattern seen across several Amazon-tributary rock-dwelling plecos: naturally narrow ranges made more precarious by river damming and habitat disturbance in the basins where they occur.
Species names such as munduruku and xikrin reference Indigenous peoples of the Amazon basin, a common convention in loricariid taxonomy that also signals how tightly some of these fish are tied to specific stretches of river. That narrow endemism is part of what makes them collectible, and part of what makes their conservation status worth watching.