Unmistakable shell due to its form and sculpture. Outline very elongate, cylindrical, with whorls not much convex crossed by little ridges prominent and granulated, the one nearer the sutur is smooth. At the base there is a fifth smooth ridge. Aperture quadrangular in form, external lip simple. The protoconch is styloide, multispiral (three whorls), cylindrical, brown, only the embryonal part is lighter, finely adorned by zigzag spiral lines. Brown in colour, with lighter granules. The average measures are around one centimetre. The periostracum is often dark brown in colour.

A tall, slender, nearly straight-sided shell of up to fifteen tumid whorls; sutures deep; five spiral ridges on last whorl, four on those of the spire, the most adapical spiral smooth or nodose, the others markedly tuberculate except the lowest on the last whorl which is smooth or nodose. Aperture small, with basal notch. Yellow or whitish. The shell is both taller and more slender than in other Cerithiopsis species. It has usually lost the protoconch, but, if this is present, it has 4-5 whorls slightly more swollen than those of the rest of the shell, each showing a complex pattern of axial lines adapically and of axial lines crossing spiral lines abapically; this pattern is usually eroded and appears only as some pitting of the surface. Up to 8mm high (protoconch present), 2mm broad; last whorl occupies 25-30% of shell height, aperture only 10-15%

The many samples (59; 174 specimens), dredged by the NNM-GANCAP expeditions, give a good overview of the various characters of this species. It is not feasible to make SEM photographs of all the shells, but with 30x magnification there are no observable differences in the microsculpture of the protoconchs. Furthermore, M. metaxae is rather variable: the number of protoconch whorls ranges from 3.5 to almost 5 (contrary to Bouchet, 1984, who quotes 3 whorls, although his SEM photograph shows 3.5 whorls). Bouchet states that the protoconch has a brown colour, darker than the brown tele-oconch. I observe that all the shells from the Madeira and Selvagens archipelago (34), from W. Morocco (1) and from the Canary Islands (52) have a protoconch of the same colour as the teleoconch (yellow-white to dark orange), sometimes a shade darker or even somewhat lighter. Only the specimens from the Gape Verde Islands (87) often have a remarkable, darker protoconch. However, I have not observed any relationship with the colour of the teleoconch: there are yellow-white shells with a dark brown protoconch and yellow-orange specimens with a protoconch of almost the same colour. All specimens from Madeira have the same coloured teleoconch (orange), contrary to those from the Canary and the Cape Verde Islands, which vary from nearly white to dark orange (often differendy coloured shells in one sample).
The teleoconch is variable in shape too. Sometimes one can find specimens with very flat whorls and shells with convex whorls in a single sample; there are shells with almost spiny tubercles on the spiral ribs, or more rounded nodules, or even nearly smooth spirals on the uppermost teleoconch whorls. The many M. metaxae dredged from considerable depths (from between 100 and 500 m) show the same variation in characters as the littoral specimens: Cape Verde Islands, depth 400-430 m, colour light orange, one shell with flat whorls, the other one with convex whorls; Madeira, depth 228-240 m, orange shells; Madeira, depth 340 m, yellow-orange shells, one with very flat whorls, the other with convex whorls and the third one with intermediate whorls. Because there is no question of uniform characters in relation to the nominal taxon, neither within the distribution area of M. metaxae, nor in relation to the depth, there is no reason to maintain a separate forma (forma excavata Locard, 1897) of this species.

M. metaxae can be found all over the Mediterranean and the East-Atlantic, in the infralittoral and in the circalittoral. It prefers either hard and detrital bottoms. Never common.