The dwarf lanternshark has a long, wide, flattened head comprising a fourth to a fifth of its total length. The eyes are large, twice as long as high, with the anterior and posterior corners acute. The nares are large and preceded by poorly developed flaps of skin. There are 25–32 tooth rows in the upper jaw and 30–34 tooth rows in the lower jaw. The upper teeth of adult males have a single cusp flanked by two pairs of smaller cusplets, while the upper teeth of females are more robust and have only one pair of lateral cusplets flanking the central cusp. The lower teeth each have a single, strongly oblique cusp, and their bases are interlocked to form a continuous cutting surface. Scattered, sparse papillae are inside the mouth and on the edges of the gill arches. The five pairs of gill slits are small.
The trunk is short, with two relatively closely spaced, large dorsal fins bearing grooved spines in front. The first dorsal fin originates over the trailing margins of the pectoral fins. The second dorsal fin has twice the area of the first and is larger than the pectoral or pelvic fins, and originates over the end of the pelvic fin bases. There is no anal fin. The caudal fin is low, with a moderate lower lobe and a ventral notch near the tip of the upper lobe. The skin is densely covered by thin, needle-like dermal denticles in a random pattern, except for the lips and the tips of the fins. This shark is dark brown with a striking and distinctive pattern of black markings on its ventral surface, a continuous or broken, fine black line along the middle of its back (but without a white band like in the similar Caribbean lanternshark), a black band on the end of its caudal fin, and a dark blotch on its lower caudal fin lobe. Curiously, some of the ventral black markings are composed of light-producing photophores, while others (including the patch behind the pelvic fins) are composed of pigment-containing chromatophores. The largest known individual is 21.2 cm (8.3 in) long.
This shark apparently inhabits the upper continental slope at a depth of 283–439 m (928–1,440 ft).