Small species with a biconic axially ribbed shell, bright white with two spiral rows of chestnut markings and a reddish-chestnut anterior tip. Shell small, biconic, 4.1 to 5.1 mm long (avg. 4.50 mm) and 2.00 to 2.20 mm wide (avg. 2.05 mm) in 15 specimens measured. Adult shells with 4 to 5 teleoconch whorls (avg. 4.3). Protoconch smooth, white, with 3 to 3.25 whorls and no real sinus. Predominant sculpture consists of rounded, slightly sinuous axial ridges (16 to 19 on the body whorl), with spiral grooves between ridges on the spire whorls and often on the body whorl. A weak subsutural groove cuts across the tops of the axial ridges. Shell translucent, white. Spire whorls have a single band of wavy axial chestnut makings in the middle of the whorl, with an additional row present on the basal half of the body whorl. These form two large blobs on the outer lip. Tip of siphonal canal in adults dark purplish brown. Aperture white. Aperture edge thickened, denticulate, with a shallow posterior notch. Parietal wall with a ridge of denticles. Body coloration: Anterior part of body cream colored except for white specks overall. Behind the mantle edge, preserved specimens are black, which can easily be seen through the shell; this may be an artifact of preservation. Operculum ovoid, with bilobed scar, no keel. Nucleus terminal, with a darker spot in the middle. Radula: In four adult male specimens dissected, lateral teeth 28 to 34 µm long by 12 to 15 µm wide, with rectangular center plates. Two radulae that were complete had 137 and 155 tooth rows. Lateral teeth have three pointed secondary cusps, the bottom one pointed and curved down, and separated from the distal two by a wide gap.

This species closely resembles Parvanachis oxillia (Duclos in Chenu, 1846) in terms of the size and color pattern. The identity of the latter has been difficult to determine, because the Chenu publication contains only figures, and localities are not given for most species. The syntype lot of Columbella oxillia, MNHN 6414, is labeled with a locality of Panama, but it does not specify whether the material came from the Pacific or the Caribbean. A photograph of one of the syntypes (http://coldb.mnhn.fr/CatalogNumber/MNHN/IM/6414) suggests that P. oxillia has a narrower form and somewhat more acute spire, with a more varicose lip and a relatively large posterior labial denticle. In this it more closely resembles P obesa (see Fig. 1A) than it does the current species, and Rosenberg (2009) lists it as a synonym of the Caribbean P obesa.