Lebiasina ardilai is distinguished from all lebiasinins by its color pattern consisting of a narrow, nearly straight primary stripe, extending from posterior to humeral blotch to near the vertical through anal-fin origin, being nearly absent in females and conspicuously marked in males; the presence of four series of dark markings at the base of the scales of longitudinal series 2–5; the faint secondary stripe running onto scales of second and third longitudinal row of scales; and the posteriorly displaced caudal blotch, not reaching the posterior tip of caudal peduncle. The new species also differs from its Guyana Shield relatives L. taphorni Ardila-Rodríguez, L. unitaeniata (Günther), L. uruyensis Fernandez-Yépez, Lebiasina yepezi Netto-Ferreira et al. and L. yuruaniensis Ardila-Rodríguez by the lack of the intermediate stripe (Ref. 93551).