Shell up to 39 mm (about 1,5 inches) in length, elongate-ovate or ovate, solid, sutures weakly impressed and narrowly incised. Whorls 5-7, apart from a protoconch of 2 white nuclear whorls, usually smooth apart from 6-10 weak basal cords and very fine longitudinal striae which are usually visible only under magnification. In some populations, however, the spiral cords are quite distinct and number from 5-9 on the penultimate whorl and become obsolete past the shoulder of the body whorl; some individuals even develop weak axial folds on the body whorl, which coincide with the white axial streaks. Aperture longer than the spire, only moderately narrow, smooth within; outer lip prominently thickened, inflected near the start but broadening anteriorly, anterior margin of outer lip occasionally with 4-9 very weak crenules, which may become obsolete through an overlaid callus; the interior swelling of the outer lip is variable and is either moderately weak or prominent. The columella is calloused, callus more prominent anteriorly, and with 4 or 5 oblique folds; siphonal fasciole short and straight, occasionally weakly calloused, siphonal notch moderately distinct. Blackish brown to black in colour, ornamented with moderately wide-spaced, longitudinal, straight or wavy white stripes, which are either continuous or centrally interrupted on the body whorl; aperture greyish-brown, usually bluish-white near the margin, columella purple-brown, folds white. Periostracum thin, brown and moderately translucent.

A very common species which is highly variable in form and colour ornamentation, and which is related to the other two similar species M. pica and M. retusa. These three species can usually be separated on the basis of the following characters: M. retusa has an outer lip which is prominently crenulate along its entire length, the base of the body whorl has strong spiral cords which are usually granulose, and the spire is very short in relation to the body whorl length. These features and the usually quite distinct colour ornamentation easily differentiate M. retusa from M. pica and M. paupercula. The latter two species are more closely similar in apertural features, both having a smooth interior swelling at the start of the outer lip, and the anterior edge of the outer lip is either smooth or obsoletely crenulate. M. pica, however, has a more elongate, cylindrical form, a distinctly less convex body whorl and a spiral sculpture which is continuous from the spire whorls to the base. In M. paupercula the body whorl is smooth apart from 6-10 basal cords.

Red Sea to Polynesia and the Hawaiian Islands.
Habitat: Under coral rocks and basalt boulders, throughout the reef-flat but more frequently towards the high tide zone; usually in shallow water of the intertidal zone but rarely found deeper than 2 fathoms.