Shell fusiform (b/1 0.34-0.40; a/1 0.47-0.55). Teleoconch whorls 4-5 moderately convex, with a rounded to minimally angular shoulder posterior to mid-whorl. Suture shallow, undulating, bordered by a moderately prominent sutural fold with two closely spaced spiral cords. Sutural ramp shallowly concave. Axial sculpture consisting of opisthocline ribs, subequal to narrower in width than intercostal spaces, extending on spire whorls from suture to sutural ramp, distinct on spire whorls, but becoming weaker on last whorl and rapidly fading on base. 14-20 axial ribs on penultimate whorl and 18-25 on last whorl. Spiral sculpture of closely-spaced, strong and narrow spiral cords. Spiral sculpture of first whorl consisting of a sutural fold, followed by 2 cords on sutural ramp and 3 cords below ramp, increasing to 6-7 on later 2 whorls. Spiral cord interspaces sculptured by none to 2-5 secondary spiral threads. Last whorl with 15-18 spiral cords on base and rostrum. Entire surface covered by coarse axial incremental lines sometimes rendering spiral cords somewhat plicate. Aperture narrow and ovate, constricted at entrance to siphonal canal. Siphonal canal long for genus, not notched terminally. Inner lip with moderately thin callus, parietal region with a pad formed at its junction with outer lip. Outer lip edge sharp, preceded by a wide, low, rounded varix. Stromboid notch moderately deep. Anal sinus moderately deep, apically rounded, and rather asymmetrically U-shaped, with only a weakly constricted entrance. Protoconch papilliform or domed, of 1,75 smooth whorls , diameter 0.76-0.98 mm. Color white with irregular light brown blotches on sub-sutural ramp.


Dimensions
Holotype: 9.15 x 3.35 mm, aperture height 4.85 mm. Paratype 1: 9.2 x 3.4 mm, aperture length 4.7 mm; paratype 10 (smallest): 6.6 x 2.6, aperture height 3.3 mm; paratype 12 (largest): 10.8 x 3.75 mm, aperture height 5.55 mm.

Otitoma nereidum sp. nov. is readily distinguished from its congeners on the basis of a combination of features including protoconch structure (paucispiral and domed), sculpture of the numerous axial ribs incised by strong spiral cords, and the relatively long siphonal canal.