Shell small, narrow, high spire, biconic. Protoconch of three whorls, smooth, conical, surface eroded, 0.82 mm wide, 0.75 mm high. 8 teleoconch whorls. Suture thin, distinct. Whorls convex with thin but distinct axial ribs which extend from suture to suture and well down body whorl, 17 on body whorl, 14 on penultimate whorl. Ribs largest at middle of whorl. 8 fine spiral ribs at anterior of shell the only spiral sculpture. Very faint axial growth lines. Shell juvenile, outer lip thin, broken, structure of sinus and presence or absence of callus cannot be determined. Columella narrow, slightly convex, with one of the axial ribs crossing surface. Aperture deep, elongate oval. Anterior canal short, broad, shallow, margin chipped. Colour glossy off-white with several strong, irregular,light brown blotches. Lower half of body whorl very faint light brown, narrow white band across centre of shell, light brown on upper body whorl; pattern repeated on upper whorls but fades out on upper part of spire. Length +/- 18 mm; width +/- 7,5 mm.

Powell (unpublished) originally included the holotype of Clavus aenigmaticus as a paratype of of C. occiduus. While the two specimens were in the same lot, they are clearly separate species. Powell himself would probably have realized this had he been able to complete the manuscript on the Clavinae. C. aenigmaticus can be readily separated from C. occiduusby having a narrower shell, the absence of spiral sculpture, narrower, more numerous axial ribs, and the colour pattern. The outer lip of C. aenigmaticus is thinner and does not form a varix, but this may possibly be due to the shell being juvenile.

Type locality
Central bank. Roebuck Bay, Broome, Western Australia.
Distribution
Known only from the type locality.