This species is distinguished from its congeners by the following set of characters: dorsal disc with dark background, with a beige or light brown, closely packed and highly convoluted vermicular pattern; one row of irregular spines on dorsal tail midline; presence of star-shaped, asymmetrical and minute dermal denticles, rarely with crown dichotomies, and concentrated over central region of disc. It is further distinguished from P. motoro (Müller & Henle, 1841) by lacking on disc ocelli formed by strong black concentric rings, a more flattened aspect of its disc; with much smaller dermal denticles, and considerably smaller eyes; from P. orbignyi (Castelnau, 1855) by lacking a dorsal reticulate pattern, presence of two angular cartilages, and lower number of total pectoral radials (modal values 97 vs. 90, respectively); from P. falkneri by having tail spines in one irregular row (instead of in 1-3 irregular rows), lower total pectoral radial count (90-93 vs. 94-100, respectively), having a proportionally much longer tail (mean values 109% vs. 93.5% of DW, respectively), by its teeth with no prominent cusps in adult males (males usually with prominent cusps in P. falkneri), and having spots on dorsal disc that are exclusively vermicular, not occurring as independent spots (many specimens with individual spots on background, these mostly circular, reniform, or oval, with diameter equal to or smaller than eye in P. falkneri) (Ref. 86911).