Guyanancistrus is a genus of suckermouth armored catfish (family Loricariidae) from the Guiana Shield, one of the oldest and most geologically stable landscapes in South America. The atlas's countries for the genus, France (via French Guiana), Suriname, Brazil, French Guiana, and Guyana, center the genus on the fast, clear, rocky rivers draining that shield. Like other plecos, Guyanancistrus species have a bony-plated body and a ventral sucker-mouth used to grip rock and graze algae and biofilm in strong current, and several are better known in the hobby by their L-number than by a common name, including Guyanancistrus brevispinis (L041). The atlas covers 8 species, ranging from about 2.5–6.5 in.
This is a genus with a real conservation signal: two of the eight atlas species are rated Endangered and three more are Data Deficient, against three not yet formally evaluated, with none considered simply Least Concern, and none yet carrying a CARES designation despite that. The Guiana Shield's isolated, rapid-fed rivers tend to produce narrow-range endemics, which makes species like these especially exposed to localized threats such as mining and damming. In the hobby, Guyanancistrus plecos are kept mainly by rheophilic-pleco specialists who replicate strong flow and high oxygen rather than by casual aquarists, and captive-bred stock remains limited for most species in the genus.