 The fins are small and very thin. The pectoral fins are rounded and lobe-like. The two dorsal fins are positioned about between the pectoral and pelvic fins. Each dorsal fin bears a slightly grooved spine in front; the second dorsal spine is longer than the first. The anal fin is absent, and the caudal peduncle lacks keels or notches. The upper lobe of the caudal fin is larger than the lower and has a notch in the trailing margin. The skin, excluding on the fins, is densely covered with irregularly arranged, nonoverlapping dermal denticles. Each denticle has a swollen rhombic shape with 10 – 40 facets on the crown. The viper dogfish is black with distinct darker markings on the underside. These markings contain large numbers of tiny light-producing photophores; more photophores are found sparsely scattered over the rest of the body, as well as in a translucent patch on the upper eyelid. The fins are translucent, and the tip of the caudal fin upper lobe is blackish. The largest known male is 47 cm (19 in) long and weighs 0.43 kg (0.95 lb), and the largest female is 54 cm (21 in) long and weighs 0.76 kg (1.7 lb).
