Shell as for M. tenuirostrum except in the following features. Maximum length about 95 mm. Protoconch of two and one-quarter to two and one-half rounded whorls, or more rarely, two whorls; varying between dome-shaped and elongate in shape; terminating in sharp, crescentic varix. Axial sculpture with angulation of ribs on first whorl usually more pronounced and, on third whorl, every third or fourth rib strengthened into varix. Shoulder spine straight or slightly curved, never very long. Spines on siphonal canal with third spine from base of body whorl relatively longer than in typical subspecies, being almost as long as, and sometimes longer than, second spine from base. Siphonal canal relatively shorter than in many specimens of M. tenuirostrum .

This species is mainly distinguished from M. tenuirostrum because of differences in protoconch morphology. The convex whorls and variable form of the protoconch of M. africanus are in marked contrast to the uniform, conical protoconch found in M. tenuirostrum. It suggests that abbreviated development, probably involving a short larval life, occurs in the East African species. There are, in addition, small differences in the teleoconch, as noted in the description. No preserved material of this form has been available to compare penial morphology.
We initially regarded this taxon as a form of M. aduncospinosus, but closer examination showed the protoconch and teleoconch morphology has more resemblance to M. tenuirostrum. The simple, non-channelled suture is, for example, one significant teleoconch character that separates M africanus and M. tenuirostrum from M. aduncospinosus. Nevertheless, the relationships and status of M. africanus are not certain, and examination of anatomical characters may require our conclusions to be revised.

East-Africa and Madagascar.