The Southern stoplight loosejaw, Malacosteus australis, is a species of barbeled dragonfish. This species is mainly distinguished from M. niger by a smaller postorbital photophore in both sexes and lower numbers of lateral photophores. It also differs in having somewhat smaller jaws, a fleshy orbit, and several subtle morphological traits. The maximum known length is 16.6 cm (6.5 in) for a male and 19.2 cm (7.6 in) for a female. Its specific epithet comes from the Latin austral, meaning "southern".