Malacosteus niger has a suborbital photophore emitting far-red light and a second emitting blue-green. Since the visual pigments of most mesopelagic animals are tuned to blue, the red beam illuminates prey without alerting it, an arrangement described as a private wavelength.
Seeing red requires special equipment. Analyses of loosejaw retinas have identified a photosensitiser chemically related to chlorophyll, which absorbs long-wavelength light and passes the energy to the fish's own visual pigment. Fish cannot synthesise chlorophyll, so the compound is thought to be acquired through the diet, most plausibly by way of the copepods the loosejaw eats, which graze on photosynthetic material higher in the water column.
The jaw is the other oddity. The lower jaw has no membrane floor, so the mouth is an open frame of bone and teeth, which reduces drag when the jaw is swung forward. How the fish then transports prey backwards without a floor to its mouth is not fully explained.