Shell cylindric-pupoid (b/1 0.38-0.45; a/1 0.44-0.55). Teleoconch of 2,5-3,5 whorls which are weakly and evently convex to roundly shouldered above mid-whorl height. Suture shallow, bordered by a moderately prominent subsutural fold with two closely spaced cords, followed by a shallow, concave sutural ramp. Axial sculpture of opisthocline ribs, subequal to or narrower than intercostal space, extending on spire whorls from suture to suture, becoming much narrower and strongly arcuate on sutural ramp. 13-16 axial ribs on penultimate whorl and 16-18 on last whorl. First teleoconch whorl with 2-3 spiral cords between whorl base and sutural ramp, increasing to 4-5 on penultimate whorl and 5-6 on last whorl. Spiral cords somewhat plicate where crossing axial ribs. Interspaces between main cords with none to 1-2 weaker cords. Sutural ramp with 1 weak spiral cord on first whorl, increasing to two on following whorl(s) (abapical one slightly more prominent); additional fine, inconspicuous cords on abapical side of sutural ramp of last whorl (in holotype). Base sculptured by 13-15 spiral cords, with none to 1-2 interstitial cords. Surface covered by dense axial incremental lines, particularly evident on sutural ramp, where they are sinuous in conformity with curvature of anal sinus. Aperture narrow and almost linear, but constricted at entrance to siphonal canal. Siphonal canal wide, expanding slightly distally, not notched. Inner lip covered with a thin callus and parietal pad. Outer lip edge sharp, preceded by a wide, low and rounded varix. Stromboid notch deep. Anal sinus deep, rounded, asymmetrically U-shaped, its entrance slightly constricted. Protoconch domed and flat, of 2,25-2,5 whorls; first whorl smooth, subsequent whorl with numerous inconspicuous, widely-spaced axial riblets and sparse microgranules. Protoconch white, diameter 0.71-0.89 mm. Teleoconch white, with outer lip edge and parietal pad tinged with brown-orange.


Dimensions
Holotype: 4.7 x 1.8 mm, aperture height 2.4 mm. Paratype 1: 4.1 x 1.7 mm, aperture height 1.8 mm; paratype 2: 4.0 x 1.8 mm, aperture height 2.2 mm.

Otitoma rubiginostoma sp. nov. is a morphologically distinctive species. The profile of the whorls and type of axial ribbing (i.e., axial ribs becoming strongly arcuate on sutural ramp) may cause it to superficially resemble O. cyclophora, but the two species are otherwise very different in numerous characters. Otitoma rubiginostoma sp. nov. is much smaller in length (up to 4.7 mm vs 13.7 mm), with fewer teleoconch whorls (2,5-3,5 instead of 4,5-5) and it has a different shape (cylindric-pupoid instead of cylindric-fusiform). O. rubiginostoma sp. nov. has strong axial ribs while in most specimens of O. cyclophora these are weak to obsolete, particularly on the last two teleoconch whorls. The protoconch of O. rubiginostoma sp. nov. is much larger than that of O. cyclophora (0.71-0.89 mm vs 0.52-0.59 mm) with different a shape and number of whorls (domed and flat of 2,25-2,5 vs papilliform of about 1,75 whorls). The two species further differ in color: O. rubiginostoma sp. nov. has a white shell with the outer lip edge and parietal pad tinged with brown-orange while O. cyclophora has a uniform pale buff shell. The new species is similar to O. vitrea and O. kecil, both of which possess large, domed protoconchs, but their teleoconch characters are otherwise too different for meaningful comparison.