A small species of Synodontis; body, at base of pectoral fins broader than high; dorsal profile of snout steep sloping until about vertical through posterior margin of orbit where-upon profile of head more gentle; complete lateral line, curving slightly dorsally above level of humeral process, further posteriorly straight, gently declining towards middle of caudal-fin base; head large (Ref. 82554).

Synodontis punu is distinguished from its Lower Guinea congeners by the following unique combination of characters: posterior border of operculum with a single hypertrophied opercular spine in sexually mature males, and caudal fin with a pair of black patches, one on the upper and one on the lower lobe (vs. both characters absent in all other Lower Guinea species except S. acanthoperca) (Ref. 82554).