The shell is, except for an unlocalized giant race, moderately small (maximum length ca. 20 mm) and fusiform. The spire is high, consisting of one and one-half convex nuclear whorls and six or seven shouldered postnuclear whorls. The suture is impressed. The body whorl is of moderate size and fusoid. The aperture is small and lenticular to kidney-shaped, with a deep, moderately broad anal sulcus. The outer apertural lip is barely erect, if at all, and crenulate; its inner surface bears five strong denticles, four grouped evenly anteriorly, and a fifth internal to the shoulder of the whorl. As is typical for the genus, the penultimate denticle, anterior to the shoulder angle, is the largest. The columellar lip is almost entirely adherent and bears two or more strong, oblique pustules on its barely erect anterior end. The siphonal canal is short, straight, and rather broadly open.
The body whorl bears six more or less promi¬nent varices. Spiral sculpture consists of eight equally strong and evenly spaced cords, one on the shoulder, six on the body, and one on the canal. Where the cords cross the varices they are developed into short, open, triangular spines, the longest at the shoulder margin.
Shell color is pale brownish-white, with dark blue-purple undertones. The aperture is maroon to purple-brown, with white denticles and pustules.
Sowerby (1834) figured a giant example of this species as Murex cataphractus, and we figure what we believe to be the same specimen (ex Calvert Collection) (PI. 23, fig. 14, herein). It represents a form that is much larger than typical M. cristatus but that is otherwise indistinguishable.

As Murex blainvillei:

The shell is of moderate size for the genus (maximum length 30 mm) and fusiform. The spire is high, consisting of one and one-half translucent, glassy nuclear whorls and seven weakly shouldered postnuclear whorls. The suture is weakly impressed. The body whorl is moderately large and fusoid. The aperture is lenticular to ovate, with a weakly defined anal sulcus. The outer apertural lip is thickened and finely, marginally crenulate; its inner surface flares anteriorly and is strongly dentate, bearing six strong denticles, the uppermost (interior to the shoulder slope) followed by a much smaller, at times ephemeral denticle, and immediately below this by a large, broad denticle and three smaller, equal-sized denticles. The columellar lip is adherent parietally, detached and weakly erect below; near the anterior end of the columella are two more or less strongly developed oblique pustules. The siphonal canal is moderately short and weakly recurved.
The body whorl bears six or seven more or less prominent varices. Spiral sculpture consists of numerous major cords alternating with minor ones, as well as fine, weak, spiral threads covering the shell.
Shell color is generally orange-brown to purple-brown, with two hands of lighter orange, one at the shoulder, one at the base of the body. The margin of the aperture is pinkish-purple.

Habitat: it lives on solid surfaces in the infralittoral zone, possibly between bryozoans and madrepora. Distribution: very common all over the Mediterranean.
Imaged shells: all of them were collected at Punta Campanella (Naples - Campania - Italy), at 45 m depth.
Notes: it is a species having a really polymorphe teleconch and changeable in its sizes, colour pattern and spines length. From individuals having no spines (inermis) to highly spiny ones (horrida). there are a lot of intermediate forms originating a great number of synonyms and varieties in form and in colour that, in our opinion, need to be probed, not only on the shell morphology, to ascertain the possible presence either of other species or subspecies.
From dirty white to rosy and to several brown tonalities, up to black in colour The animal is light red in colour. Protoconch not much changeable and globose in form, with one turn and half of spiral, sculpture made by a close series of non aligned tubercles thinning in the last part near teleconch. This species does not change very much its morphology during its several growth stages. The adult specimens average measures are around 20 mm in height but there were also found individuals around 40 mm in height.