Shell rounded, rather depressed, fragile, with a small keel at the periphery. Protoconch of about 17, smooth whorls, of about 460 µm diameter. It continues to the teleoconch with a scarcely evident separation. Teleoconch of about 172 whorls, with rapid increase. Dorsally, the whorls are evidently convex with very numerous curved, prosocline growth lines; ventrally, very slightly convex, with the same growth lines, which are more evident and form an S-shaped part near the periphery. A spiral depression is close to the peripheral keel. With magnification it is possible to see very small tubercles on the uneroded parts. Umbilicus wide, showing the previous whorls. Aperture nearly ovoid a little extended dorsally. Columella curved, nearly vertical, outer lip sharp, with a small notch where the peripheral border ends. Dimensions: Holotype is 3.7 mm in maximum dimension (diameter). The largest shell examined was 5 mm. Animal: not observed alive. Only one dried animal was found in a shell. Apparently, its morphology is similar to other Rissoidae. Operculum a little ovoid, paucispiral and with a subcentral nucleus. Radula taenioglossate. Central tooth very wide with its lateral parts expanded, 2 basal sharp denticles, ventral margin wide U-shaped; cutting area with a prominent main cusp and 5-6 smaller denticles at each side. Lateral teeth with a large cusp and 4-6 small sharp denticles at each side. Marginal teeth large and narrow; the inner marginal tooth with 8-10 very small denticles on its outer margin; the marginal outer tooth sickle-like, very narrow and sharpened distally, without apparent denticulation.

D. apertus is easily differentiated from the other species of the genus known from West Africa, because it is larger, more rounded, and its basal growth lines have a spiral depression at the periphery. Comparisons with the closest species are as follows:
- D. costulatus is more depressed, with smaller aperture, the rate of increase of the shell more rapid, the growth lines less curved, and more evident dorsally.
- D. militare is smaller and with a spiral cord in the base near the periphery and sometimes others less evident. The periphery is more rounded.
- D. radians is very small, with numerous axial ribs and one basal spiral cord.
- D. exmilitare also has one spiral cord on the dorsum and in the base.

The species was collected from Guinea Conakry to Angola, excluding the islands of the Gulf of Guinea.