Hemiancistrus is a genus of suckermouth armored catfish in the family Loricariidae, native to river systems across northern and central South America; the atlas's 14 species are recorded from Brazil, Ecuador, Uruguay, Venezuela, Colombia, French Guiana, and Suriname. Members share the loricariid body plan — a flattened, bony-plated body and a ventral sucker mouth used to graze algae, biofilm, and wood — and span a wide size range within the genus, from about 3 in to nearly 15.5 in, putting the larger species among the bigger plecos kept in aquaria.
The genus's best-known aquarium representative is Hemiancistrus subviridis, the green phantom pleco, prized in the hobby for its striking blue-green body and orange-edged fins; it and several relatives also circulate under L-number codes used by pleco collectors, such as Hemiancistrus guahiborum (L106). Most Hemiancistrus are grazers and detritivores that do well on a wood- and vegetable-heavy diet in a well-filtered, current-rich tank, though many of the 14 atlas species are seen only rarely outside specialist collections. Conservation-wise the picture looks comparatively settled for a South American catfish genus — nine species assessed Least Concern — though a Near Threatened, an Endangered, and several Not Evaluated species show that part of the genus remains at risk or unassessed.