Hexaplex radix: The shell is large (maximum length 150 mm) and massive. Its spire is low, with two and one-fourth nuclear whorls and seven weakly shouldered postnuclear whorls. The suture is shallow and generally obliterated by the succeeding whorl. The body whorl is very large and globose. The aperture is large, broad, and ovate, with a broad, moderately shallow anal sulcus and a broad opening anteriorly into the siphonal canal. The margin of the outer apertural lip is strongly dentate, with a deep indentation at the shoulder spine, and projecting most strongly where it forms a compound labial tooth near the anterior end of the aperture. The columellar lip is completely adherent and bears a spiral ridge from the outer margin of the parietal region to within the posterior portion of the aperture. The siphonal canal is broad, moderately long, narrowly open on the right side, and slightly recurved; the region adjacent to the canal bears sizable portions of former canals forming a strong ridge, beneath which there is a deep false umbilicus.
The body whorl bears six to 11 strongly spinose varices. Spiral sculpture consists of several major cords interspersed with minor cords: two majors are developed on the shoulder, one is appressed to the suture, and one lies nearer the shoulder edge; below the shoulder are five additional cords of more or less equal development; and the canal bears two additional major cords. Where the major cords intersect the varices they are developed into coarse, slender, erect, foliaceous projections. The foliated portions of these projections are recurved and may be short and blunt or extended into spinose processes. Sculpture is diminished on the spire, largely because of the limited exposure of each whorl. Visible axial sculpture proceeds obliquely across the spire.
The shell is white, with blackish-brown on the spiral elements and foliations. The proportion of white to black is variable.

Hexaplex radix: A high degree of polymorphism is exhibited in the shell of this species. The northernmost form , known as M. nigritus Philippi, 1845, is relatively high-spired, with six to nine varices. The form from the center of the range (north of Mazatlan, Mexico, to somewhat south of Manzanillo. Mexico),. which is known as M. ambiguus Reeve, 1845, has a somewhat lower spire, eight to ten varices, and a proportionately more massive body whorl. Specimens from the southern portion of the Panamic province, known as M. radix, have a still heavier, more globose body whorl and eight to 11 densely arranged varices. Other names given to this species, based primarily on young shells with long, beautifully developed spines, are M. nitulus Broderip, 1833, and M. callidinus Berry, 1958; in all other characters these forms are indistinguishable.

Hexaplex radix: Upper portion of the Gulf of California (Mexico) to Peru.