Brachytoma rioensis is a species of sea snail, a marine gastropod mollusk in the family Pseudomelatomidae.

(Original description) The fusiform shell is pale brown with whitish ribs.

The rest are concave above the convex, oblique ribs (ten on the penultimate whorl) with transverse tubercles on the middle caused by spiral lirae passing over them.

The outer lip shows a strong external varix a little way from the thin brown finely denticulate edge.

The posterior sinus is moderately deep and rounded :The columella is smooth, with a thin callus united above to the end of the outer lip.