This species is distinguished from its congeners, except S. ciliatus, S. melanops, S. mystinus, by having a dark gray, blue, brown, or black body coloration; scales on mandible; weak or no head spination; differs from S. ciliatus and S. melanops by the maxilla not extending beyond the posterior margin of the pupil when the mouth is closed; from S. ciliatusby having 4 bars of dark pigmentation that extend across the head and nape (vs. almost uniformly dark head coloration with 2 faint bars below the orbit) and with 26-27 vertebrae (vs. 28-29); differs from S. melanops by having a uniform, light blue-gray, speckled pattern on the trunk (vs. darker black-gray coloration with irregular areas of dark pigmentation ranging from speckling to blotches) and by having dark dorsal-fin membranes without dark spots; differs from S. mystinus by the brownish-blue to blue-gray trunk with distinct lighter blue-gray speckles (vs. steel-blue to greenish-blue body coloration and large, dark blotches which are also apparent in preserved specimens) - this character is indistinct in many individuals under 10.0 cm SL; differs from S. mystinus with individuals over 15.0 cm SL, by having the ventral margin of head and ventrum generally flat (vs. rounded) and by the allometric development of the symphyseal knob, length of dentary symphysis 4.0-7.0% HL (vs. 2.6-5.7% HL) - although these ratios overlap, the symphyseal knob length differs diagnostically among specimens of equal size over 15.0 cm SL (Ref. 103574).