Irregularly cylindrical, posteriorly pointed, with dorsal umbonal ridge from umbo to posterior end, inflated, umbones near (but not at) anterior end and curving anteriorly and inward, fragile, white with thick brown periostracum tufted on posterodorsal slope, with fine, divaricating radial riblets that are absent from center of the valves and that curve posteroventrally from dorsal ridge; interior bluish white, margin finely denticulate, hinge with few teeth; living bored into soft rock or dead coral. North Carolina to Florida, Bermuda, Bahamas, West Indies, Gulf of Mexico, Caribbean Central America, South America (Suriname, Brazil), also eastern Pacific. Length 14 mm (to 19 mm). Syn. chenui Recluz, 1842.

Gregariella coralliophaga (Gmelin, 1791) Coral-cating Mussel Distribution: North Carolina to Texas; West Indies; Bermuda; Brazil. Size: 18 mm (¾4 in). Description: Color of exterior white, rarely with purplish-bluish stain; shape robust, broad, rectangularly elongate; sculpture cancellate with periostracum mainly covering umbonal keel; umbo located at extreme anterior end and rolled inward; lateral teeth on both sides of umbones, prominent on lower portion, no cardinal teeth; thin hinge line. Habitat: Vacated shells and old bore holes, mainly offshore. Depth range 0 to 101 m (330 ft). Remarks: There is some question as to the differences between G. coralliophaga and G. opifex. Abbott (1974) considers G. opifex a synonym of G. coralliophaga. Here we separate the two. See Lipka (1974); Odé (1979a); Hicks et al. (2001).