Shells are all small to moderately large, with a high spire and a short to moderately long siphonal canal. The sculpture is important in distinguishing Murexsul species from those of other muricid groups. In the type species and in unworn examples of other species the varices are composed of numerous erect lamellae. Even more significant is the gap in spiral sculpture apparent immediately below the base of the body—a gap found, as well, in Murexiella and Favartia. The canal generally bears several longish, straight spines.
The radula, protoconch, and internal anatomy corroborate the above shell-based distinctions.

Murexsul Iredale 1914. Ovate, sometimes narrowly umbilicated, axially ribbed, tending to develop varices carrying hollow spines on the body-whorl; spiral ribs numerous, narrow, lounded; spire conical, gradate, rather higher than the mouth; protoconch small, of barely two whorls, smooth, flat vertically, topped by a fairly sharp keel, the summit a marked pit, the tip being rather immersed; mouth ovate; outer lip angled above; canal moderate, oblique, recurved, narrowly open; umbilicus narrow, distinct; operculum horny, with nucleus scarcely terminal. Type—Murex octogonus Quoy & Gaimard 1833 (New Zealand).