Cerithium atromarginatum Dautzenberg and Bouge, 1933. (Synonyms: Cerithium maculosum Mighels, 1845, non Kiener, 1841; C. nassoide Sowerby, 1855.) Length, 14 mm; diameter, 5 mm. Shell: conic-obese; solid; with obscurely beaded spiral threads; fawn mottled with light and dark brown. Spire: protoconch of three and one-half red-brown whorls, the apical smooth, the others with fine axial ribbing and spiral keels; teleoconch of four or five slightly inflated whorls; suture shallow. Sculpture: obscurely beaded spiral threads equal in diameter to the interspaces; with occasional axial varices. Aperture: ovate; outer lip thick; siphonal canal short, barely recurved. Color: fawn mottled with white, light brown and with occasional splashes of dark brown. Animal: tentacles, mantle and foot creamy white mottled with light and dark brown; proboscis and siphon also flecked with yellow.
These cerithids are common buried in sand and under rocks and rubble in tide pools and in the algal-sand mat on solution benches. Shells are occasionally found in sediments to depths of 13 m. The veligers are bilobed; metamorphosis occurs when three to three and one-half whorls are complete at a length of 325 µm (J. B. Taylor, 1975).
C. atromarginatum occurs throughout the Indo-West Pacific, from Mauritius and the Cocos-Keeling Islands (Maes, 1967) to the Ellice Islands (Hedley, 1899), the Society Islands (Dautzenberg and Bouge, 1933) and the Marshall Islands.