Loosejaws have a single round nostril on each side of the snout, palatine bones without teeth, and a large red tear-drop shaped accessory light organ below the anterior margin of the eye.
Kenaley, C.P. 2007. Revision of the stoplight loosejaw genus Malacosteus (Teleostei: Stomiidae: Malacosteinae), with description of a new species from the temperate Southern Hemisphere and Indian Ocean. Copeia 2007(4): 886-900.