Shell to 85.0 mm in length, fusiform-elongate and solid, width 24-28% of length, teleoconch of 8-9 whorls which are convex or subangulate, protoconch unknown. Sculptured with narrow, elevated spiral cords which number 5-6 on the penultimate and 12-15 on the body whorl, siphonal fasciole calloused in senile specimens and with an additional 5-6 oblique cords; interspaces concave, axially striate, striae usually more prominent on spire whorls, and sculptured with a central spiral thread and occasional (up to 10) finer macrostriae. Aperture equal in height or longer than the spire, 47-56% of total length, smooth within, outer lip convex or subangulate. foliated on the edge, columella straight or slightly twisted, narrowly calloused and with 4-5 oblique folds, last two anterior folds usually feeble, siphonal notch distinct. White,'cream or pale orange-brown under a dark greenish-brown to almost blackish, opaque periostracum, aperture white.

This species is very closely related to S. attenuata (Broderip), it has the same geographical distribution and has been synonymized with S. attenuata by some writers. Immature specimens of S. gigantea cannot be separated from S. attenuata and it is suspected that S. gigantea has been based on a larger, more mature specimen than S. attenuata. For this reason S. gigantea is only tentatively accepted as a valid biospecies pending further population studies of the two taxa.

Range - From the Gulf of California, Mexico, to Ecuador. From the intertidal zone to 60 m. Although Z. gigantea is typically a subtidal species, Shasky (1975) reported it from the intertidal region of Panama City.