Shell small (SL < 3.3 mm), thin, white, ovately conical, of moderate height (SH/SL = 0.34). Apex just posterior of center (P/SL 0.53). Protoconch slightly below apex, 210 µm in length, posteriormost portion enveloped by posterior slope of shell. Protoconch sculpture unknown, worn in all available specimens. Teleoconch sculpture of raised radial ribs, with two weak radial threads between adjacent ribs. Anterior slope weakly, evenly convex, posterior slope straight. Aperture ovate, slightly narrower anteriorly. Shell edge thin. Periostracum thin, finely tufted along radial ribs and threads, extending beyond shell edge.
External anatomy : Animal poorly preserved. Eyes lacking, epipodial tentacles present, oral lappet broad .
Radula: Rachidian tooth narrow, with single triangular cusp on raised shaft. First and second lateral teeth each with four cusps, third lateral tooth with single cusp. Pluricuspid tooth with large central denticle, flanked by single denticle on outer edge, two weaker denticles on inner edge.

Among the western Atlantic species, Cocculina fenestrata most closely resembles C. emsoni. While lacking the characteristic lanceolate outline and raised ridges of C. emsoni, C fenestrata does share sculpture consisting of radial cords and threads, a periostracum that extends beyond the shell edge, and narrow rachidian teeth that have single cusps on a raised shaft.

This species is presently known only from the type locality, off Buritaca, Palomino, Colombia, at a depth of 504 m.