Lightly built, the smooth lanternshark has a large head with a pointed snout, large oval eyes, and nostrils with short anterior skin flaps.
There are 22–31 tooth rows in the upper jaw and 30–53 tooth rows in the lower jaw.
Each upper tooth has a narrow smooth-edged central cusp flanked by 1–2 tiny cusplets; mature males over 38 cm (15 in) long grow additional pairs of lateral cusplets with age.
The lower teeth are smooth, knife-like, and angled, with their bases interlocking to form a continuous cutting surface.
The five pairs of gill slits are long.

The first dorsal fin bears a stout spine in front and originates over the free rear tips of the rounded pectoral fins.
The second dorsal fin is much larger than the first and has  a longer spine.
The pelvic fins are low and angular, and there is no anal fin.
The caudal fin is short and broad, with a well-developed lower lobe and a ventral notch near the tip of the upper lobe.
The skin is covered by many widely spaced, small blocky denticles not arranged in regular rows, giving it a smooth appearance.
The coloration is a uniform dark brown, with a faint black mark over the bases of the pelvic fins extending both forward and backward on the flank.
The smooth lanternshark is very similar to but smaller than the blurry lanternshark, attaining a length of 50 cm (20 in).
The two species differ in a number of anatomical characteristics, but can be most reliably distinguished by the number of turns in their spiral valve intestines (10–13 in E. pusillus versus 16–19 in E. bigelowi).
Lightly built, the smooth lanternshark has a large head with a pointed snout, large oval eyes, and nostrils with short anterior skin flaps. There are 22–31 tooth rows in the upper jaw and 30–53 tooth rows in the lower jaw. Each upper tooth has a narrow smooth-edged central cusp flanked by 1–2 tiny cusplets; mature males over 38 cm (15 in) long grow additional pairs of lateral cusplets with age. The lower teeth are smooth, knife-like, and angled, with their bases interlocking to form a continuous cutting surface. The five pairs of gill slits are long.
The first dorsal fin bears a stout spine in front and originates over the free rear tips of the rounded pectoral fins. The second dorsal fin is much larger than the first and has  a longer spine. The pelvic fins are low and angular, and there is no anal fin. The caudal fin is short and broad, with a well-developed lower lobe and a ventral notch near the tip of the upper lobe. The skin is covered by many widely spaced, small blocky denticles not arranged in regular rows, giving it a smooth appearance. The coloration is a uniform dark brown, with a faint black mark over the bases of the pelvic fins extending both forward and backward on the flank. The smooth lanternshark is very similar to but smaller than the blurry lanternshark, attaining a length of 50 cm (20 in). The two species differ in a number of anatomical characteristics, but can be most reliably distinguished by the number of turns in their spiral valve intestines (10–13 in E. pusillus versus 16–19 in E. bigelowi).
Smooth lanternshark