Small, turriculated shell, reaching about 6.5 mm in length; width about 48 % of length. Papillose paucispiral protoconch consists of 1,5 smooth pinkish whorls. Teleoconch consists of 4 nearly straight whorls with large subsutural ramps and angulated shoulders. Straight spire outline. Each whorl with about 12 axial ribs and V-shaped interspaces, entirely sculptured with fine spiral cords. About 10 spiral cords on penultimate and 14 spiral cords on body whorl. Aperture about half of the entire shell, wide and lirate within. Columella with 4 strong folds, a fifth one often nearly invisible. Siphonal canal short, wide and slightly recurved. Colour pattern: Shell colour yellowish translucent. Protoconch, subsutural ramp and neck pinkish. Spire whorls with a white band below the shoulder, followed by a row of brown dots in the interspaces of the yellowish opaque central area of the whorls. Columellar folds pink.

Vexillum (Pusia) aequatoriensis n. sp. resembles V. (P)rubrum (BRODERIP, 1836). But the protoconch of the new species is papillose paucispiral (1,5 whorls) instead of conoidal multispiral (~ 3 whorls). Both species have large subsutural ramps, but in V (P.) aequatoriensis n. sp. the shoulder is angulated, whereas in V (P) rubrum it is rounded. Protoconch and siphonal fasciole are reddish/pinkish in both species. The small white band beneath the shoulder is also the same, but in the new species a translucent yellow area occurs below this band and ends at the siphonal fasciole, whereas in V. (R) rubrum only a narrower grey band occurs, which does not reach the aperture and ends with a brown line branching into the grey band at the interspaces. The dark brown dots in the interspaces of V. (P) aequatoriensis n. sp. are not connected by a line or band.
The new species also has similarities to V. (Costellaria) pagodula (HERVIER, 1897) because of the large subsutural ramp, but this is the only similarity. V. (C.) pagodula has at least one more whorl, broader (and therefore fewer) axial ribs, but smaller interspaces. The protoconch is dark brown, the subsutural ramp and the peripheral band on the body whorl are also brown or olive coloured. In the new species, the protoconch and the subsutural ramp have the same rose colour as the siphonal fasciole. And the white band below the shoulder is narrow, whereas in V. (C.) pagodula, all the spire whorls are white and the characteristic yellow band with brown dots is missing. V. (P.) aequatoriensis n. sp. also is comparable to V. (P.)goubini (HERVIER, 1897) because of its brown dots in the interspaces. But V. (P.)goubini is much more slender, has an additional whorl and there is no subsutural ramp because the coronated shoulder is directly at the suture. Also, the colouration is different. Protoconch and siphonal fasciole are white instead of rose, the shoulder is reddish brown instead of rose and white and the brown dots in the interspaces are more reddish than brownish. The sister species V. (P)plurinotatum (HERVIER, 1897) in addition is distinguished by three instead of one row of these reddish dots and a smaller size (4 vs. 6-7 mm).

Holotype: Indonesia, Irian Jaya, West Waigeo Island, East Jeben Island, 0°29,039"S-130°20,419"E, on coral slope in rubble and sand patches at 2-30 m depth, 6.3 x 2.9 mm, ah: 3.5 mm, SMNS-Z1-0073914 (ex MH).
Distribution: Malaysia, Indonesia and Papua New Guinea in the equator region.