Description. Holotype: Shell of medium size for the genus, height 8 mm, width 3.3 mm, solid, fusiform, biconic, rather slender, H/W=2.424. Protoconch paucispiral, shiny, of 1.3 barely convex whorl, d 0.30 mm, Do 0.475 mm, DM 0.65 mm, h 0.50 mm, sculptured by sparse rare microgranules. Protoconchteleoconch boundary well marked, flexuose, opisthocline. Teleoconch of da 4.8 convex whorls, first two whorls more convex. Sculpture starting with 4 spiral cordlets crossed by 17 axial opisthocline ribs on the first whorl. Third cordlet more pronounced giving a keeled outline to the first two whorls. Additional spiral cordlets between the adapical ones, and between the suprasutural one and the suture. Last whorl sculptured over the entire surface by 29 fine spiral cordlets, equidistant, of equal size, half as broad as the interspaces, of which 9 above the aperture. Axial ribs (16–17) present only on the first 2.5 whorls. Axial ribs of variable strength producing weak nodules at the intersection with the spirals. Two weaks well spaced columellar folds, the posterior with a slightly bifid outer tip. Growth lines visible over the entire surface. Outer lip sharp, thickened internally with 10 elongated
denticles, disposed in pairs. Anal sinus shallow. Siphonal canal short, and wide. Coloration light beige in the background, with darker vertical flammulae, and intense darker subsutural blotches. Soft parts unknown.

We would normally be rather reluctant in describing a new species based on a single specimen.
However, the holotype of M. cossyrae n. sp. is so distinct with its rather slender shell (H/W 2.424) and the spiral sculpture, regularly spaced apart and more pronounced than the axial one that it could not be considered an anomalous specimen of any of the other species. M. bogii n. sp. has a lower H/W (1.956–2.407), has a smaller number of axial ribs on the first whorl (14 v. 17 in M. cossyrae n. sp.) and a denser and less pronounced spiral sculpture. M. olivoidea has a lower H/W (2.021–2.306), smaller apical diameters, more spirals on the last whorl (34–39 v. 29 in M. cossyrae), 3 spirals on the first whorl (v. 4).

Known only from the type locality, off Pantelleria Is., Central Mediterranean Sea.
Recent, although a possible fossil origin (from a reworked assemblage) cannot be ruled out. Only one empty shell in bioclastic sediment, from 430 m depth. Found sympatric, often at different depths, with M. karpathoensis.