There is a red stripe on the lower jaw running to the photophore. The third is tiny and round, located between the eye and the large red photophore. The ink sac contains a dumbbell-shaped photophore. The postorbital photophore in this species is larger than in "M. australis". It also differs in lateral photophore count, as well as in morphological characters. Another spherical photophore is located at the base of the tentacular club. The red photophore of "Malacosteus" thus allows it to illuminate prey without being detected. The photophore uses bioluminescence to produce light to entice a victim. The anus is at the anal fin, there is no photophore. The photophore is found on the dorsal fin of the pacific viper. This photophore is green in young fish and becomes more red as it ages.