Shell small, to 19.5 mm, fusiform, truncated anteriorly, up to 11,25 convex, bulging whorls; body whorl an approximately 57% of shell height; aperture moderately wide, columella straight. Protoconch approximately 2,5 smooth whorls, well rounded, the first not immersed in the second. Axial sculpture of arcuate ribs on the first teleoconch whorl, which transition into straight ribs by 2nd broad, and the remaining ribs, which are bulging, round-crested and extend from suture-to-suture, broader than intercostal spaces; reduced, narrower, and slightly recurved on shoulder. Ribs number 9-10 on the penultimate, and 7-10 to the varix on the body whorl. Growth striae cover entire shell surface; striae on the trailing sides of ribs run parallel with the ribs; striae on the leading side of the ribs cross over ribs obliquely at rib shoulders; striae in the sulcus are recurved, echoing the shape of the anal sinus. Varix wider and more prominent than the adjacent ribs, located about 1/4-1/3e turn back from the edge of the outer lip. Spiral sculpture of 2-3 raised threads on anterior portion of teleoconch whorls, and approximately 17 below the periphery of the body whorl, fairly evenly spaced up to the anterior fasciole. Between the threads are 5 or more finer microscopic threads or grooves, approximately 40/mm on the holotype, which impart a matte finish to shell surface. Sulcus narrow and concave with curved extensions of the ribs and growth striae whose shape reflect the round outline of the anal sinus. Outer lip thin, edge forming a low arc from and congruent with the anal sinus to the stromboid notch. Anal sinus deep and round, constricted by parietal lobe, almost closed in older specimens, edges flared, angled away from shell axis. Inner lip margined, thick at anterior end, thinner on parietal wall, and ending posteriorly in a large tubercle. Anterior canal deep, open, and slightly twisted to the right when viewed ventrally, end of canal flared up dorsally, notched; anterior fasciole slightly swollen; with about 8 spiral threads. Color yellowish white to white base with 3 narrow brown bands, about equal in width, the posterior-most one broken by the crests of the ribs forming a row of brown spots. Only two bands are visible on the spire whorls, one at the suture and the row of spots just above the whorl's periphery.

Decoradrillia harlequina is an appropriate representative of the new genus because it is widely distributed throughout the Caribbean and possesses strong generic characteristics as the type of the genus should: broad bulging ribs, enlarged, rib-like varix (not hump-like), elongate anterior canal, and presence of closely-packed wavy microscopic spiral threads. Variability. The average total length of 16 unbroken specimens is 15.7 mm (11.6-19.5 mm) and their W/L ratio is 0.375. The most visible characteristic, its color pattern, is surprisingly constant among specimens examined so far. Those from Tobago I. have a brown, not white anterior fasciole. Identification. Decoradrillia harlequina is not likely to be confused with its congeners on account of its color pattern. It is most similar to Fenimorea petiti Tippett, 1995 but differs in having more swollen ribs, closely packed spiral threads, not the rows of "pits" formed by spiral grooves in F. petiti, and a different coloration.

Range and habitat. Bahama Is. (Grand Bahama I.); Greater Antilles (Jamaica), Lesser Antilles (St. Martin; SVG; Grenada); South America (Trinidad & Tobago: Tobago I.; Colombia: San Andreas Is.); Panama (San Bias Is.: Hollandes Cays); and Belize (Ambergris Cay). Published photographs of specimens from Jamaica (Humfrey, 1975) and Colombia (San Andrea Is.) (Daccarett & Bossio, 2011) are identifiable as this species. This species has been collected in coral reefs in mostly a rather narrow depth range of 10-29 m. Most specimens exhibit evidence of predator attacks with severe repairs on the spire and body whorls, not counting missing lips, post-varix (which may have been broken in handling). The shell is also very solid, probably a defense against this high predatory pressure.