In form similar to the "vidua" form of C unizonalis; breadth/length 0.35-0.46; suture weakly crenulate, deeply but very narrowly recessed under edge of following whorl, adpressed to previous whorl; aperture oblong-ovate, slightly contracted basally, aperture/total length 0.28-0.39; base moderately broad, truncate, not notched, fasciole weak. Anal sinus a widely open "U", parietal pad large; stromboid notch shallow.
No subsutural cord or sulcus. Terminal varix slightly behind lip, broad and rounded. Axial ribs initially arcuate and reaching suture, on later whorls opisthocline and feeble on subsutural slope and at parietal/columellar junction, forming a low to distinctly projecting angle at periphery, in t/s bluntly angular, wider than intervals, 8-14 on penultimate whorl. Spiral sculpture restricted to 8-11 declivous ridges on rostrum. Surface slightly glossy, microscopically cancellated by dense, spiral threads, and very slightly coarser collabral ones.
Subsutural and peripheral region white, remainder deep (occasionally light) reddish-brown, sometimes paler brown at anterior end; subsutural region tinged with pale brown or greyish, and bearing regular brown to dark brown blotches or rectangles at irregular intervals; base of last whorl with 1-2 rows of white dots or feeble nodules, at about parietal level; a brown line is often present at lower edge of subsutural concavity.
Protoconch domed, of about 1.75 smooth evenly convex whorls, diameter about 700 µm, height about 610 µm. Posteriormost 0.25 of whorl with very fine incremental slightly arcuate lines. Protoconch-teleoconch transition indistinct, marked by change in the shape of suture.
Measurements. Largest and smallest adults 12.9 x 5.3 mm and 10.6 x 4.4 mm, respectively.
Radula: Rachidian narrow, shallowly notched anteriorly, with medium-sized median cusp and fine side denticles. Lateral teeth broad, arcuate, with 16 cusps, 3rd-6lh from inner side being the longest and gradually diminishing in length towards outer side, where they evanesce. Marginal teeth long, with slightly broad short blade about 1/4 of teeth length. Blade anterior edge slightly thickened. Accessory limb very weak. About 40 rows of teeth.

Historically, there has been doubt as to the distinction between Clavus protentus and C vidua [unizonalis]. However, the numerous New Caledonian samples in the MNHN collection confirm its validity. C protentus does not exceed 13.5 mm in length, against at least 20 mm for adult C unizonalis, and the white subsutural region shows distinctive brown blotches at irregular intervals, never seen in C unizonalis; the peripheral nodules in C protentus are never squamiform, the suture is more narrowly recessed under the following whorl, and the parietal pad is paler; occasionally a brown line is visible between the upper end of the nodules. Finally, the surface in fresh C protentus is slightly glossier than in C. unizonalis, and the microsculpture relatively stronger. As in other members of this species complex, the peripheral angle varies in strength between individuals.
Most of the LIFOU 2000 samples are immature, and even the adults among them have not attained the dimensions of the worn shells that passed through the hands of Hervier.
Historically, there has been doubt as to the distinction between Clavus protentus and C vidua [unizonalis]. However, the numerous New Caledonian samples in the MNHN collection confirm its validity. C protentus does not exceed 13.5 mm in length, against at least 20 mm for adult C unizonalis, and the white subsutural region shows distinctive brown blotches at irregular intervals, never seen in C unizonalis; the peripheral nodules in C protentus are never squamiform, the suture is more narrowly recessed under the following whorl, and the parietal pad is paler; occasionally a brown line is visible between the upper end of the nodules. Finally, the surface in fresh C protentus is slightly glossier than in C. unizonalis, and the microsculpture relatively stronger. As in other members of this species complex, the peripheral angle varies in strength between individuals.
Most of the LIFOU 2000 samples are immature, and even the adults among them have not attained the dimensions of the worn shells that passed through the hands of Hervier.

Apparently endemic to Lifou, Loyalty Islands, intertidal to 45 m, live to ca 25 m.