A rather small - 2.5 to 5.6 mm - Emarginula with a broad oval shape when seen from the top. Thin shelled and a little translucent. When seen from the side, low shaped, the apex turned backwards, but sunken almost inside the dorsum. The backside of the shell sloping, the apex at about 1/5 from the end of the backside of the shell. In front, the selenizone is quite broad and deeply incised: almost 1/3 of the length between the apex and the periphery. Behind the slit which is bordered in intact specimens with two high thin raised shields, one on each side, a long selenizone that runs up to the apex, over the top of the shell. In the selenizone, small septa, which become clearly visible and bigger as one approaches the slit. There are 24 large radiating ribs in the holotype. Smaller radiating ribs in between the large ones. They are crossed by concentric ribs, numerous. Where the concentric ribs and the radiating ribs cross, knobs are formed, giving they ensemble of the surface a pearled appearance. The periphery is indented and looks irregular, but the dents appear where big radiating ribs end. Shells are translucent and come in two color forms: either white, like glass, or yellow colored. We refer again to the photos for a general understanding of shapes, sculptures and coloration.

We here compare the species with the only other Indo-Pacific species with which it was confused in the past and that bears some similarities.
* Emarginula puncticulata A. Adams, 1852 This Emarginula, described from Mindoro, Calapan, is more than 3 times the size of a large E. gustavi n. sp. Moreover, the ribs do not bear rounded knobs and are less obvious in the front of the shell, the apex is raised and pointing upwards, not inwards as in E. gustavi n. sp.

TYPE LOCALITY: Philippines. Mactan Island. Hadsan. 125 m deep. DISTRIBUTION
At present only known from the Philippines: Mactan Island; Cebu, Liloan; Leyte; Olango Island; Bohol, Balicasag Island. Collected between 50 and 200 m.