"Lasiancistrus" species are medium-sized loricariids, with the largest being about 19.0 centimetres (7.5 in) SL. The body is strongly dorsoventrally compressed and moderately wide. The head and nape are gently sloped to the insertion of the dorsal fin. The ventral surface of the fish is flat. The head contours are smooth. The eyes are small to medium. The caudal fin is slightly emarginate to forked, with the lower lobe longer than the upper lobe. The dorsal flap of the iris is present. The lips are wide and fairly thin; the upper lip has small, round papillae and the lower lip has medium-sized papillae anteriorly and smaller ones posteriorly.