Atlantilux exigua: Shell size small for the new genus, to 6.0 mm in length, shape elongate-ovate. Protoconch of 1.5 bulbous tan to dark brown glossy whorls. Teleoconch of 4 to 4.5 whorls with steep subsutural ramps; spire whorls convex, sculptured with 10 to 11 strong and well rounded, evenly spaced, axial ribs; body whorl sculptured with about 12 to 14 axial ribs which become obsolete and narrowly arranged towards the aperture. Axial sculpture is consisted of a central elevated belly, which is enhanced by numerous very fine spiral striae, and bilateral depressed slender branched threads. The number of adapical branches of depressed riblets are 2 to 3 and that of abapical branche of depressed riblet is mostly 1. Sutures crenulated and well defined. Siphonal fasciole with 2 to 3 densely arranged oblique cords. Columella with 4 folds which decrease in size anteriorly. Aperture shorter than spire; inner lip thin, smooth and lack of parietal callus; outer lip simple, extending externally, inferiorly then medially. Siphonal canal short and wide; siphonal notch distinct and slightly recurved. Aperture with transverse lirae. Ground color of shell ivory white. One broad white band, overlying elevated central bulk of axial ribs, ornamented with two olive bands, which divide rib bulk into three equal parts. Two dark brown to light brown bands overlap the depressed zone of branched slender riblets, below the suture and on lower half of body whorl. Both brown bands are interrupted by branched white threads communicating with central ribs. Columella, folds and siphonal fasciole, beige; columellar folds and upper pole of aperture are stained with dark brown spots. Cernohorsky (1978) makes a preliminary review of Caribbean-Atlantic COSTELLARIIDAE species based on type-specimens and has contributed in no small measure to the exact identification of taxonomically dubious Vexillum exiguum.

Atlantilux exigua: Wide distribution in the Caribbean and adjacent North Atlantic Ocean; southern Florida to Cuba, U.S. Virgin Islands, Barbados, Grenada, Bahamas and Cayman Islands; Honduras; Quintana Roo, Mexico; also reported by Peile (1926) from Bermuda. From the intertidal zone to sunlit zone depth, fine mud and sand.