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Marine Animal Encyclopedia

Stoplight Loosejaw Malacosteus niger

The loosejaws are deep-sea predators that get their name from the fact that their jaws are seemingly hinged in multiple places, allowing them to be opened widely and to swing down and out in order to snare relatively large prey. Furthermore, the mouth is not covered with skin, so these fishes rely on their long, needle-like teeth to capture the prey and manipulate it for swallowing whole.

The Stoplight Loosejaw is named for the two specialized light-producing organs that are located below each eye. One is green and one is red. Producing light in these two colors increases the ability of the Stoplight Loosejaw to see and attack its prey. There is very little light at the Stoplight Loosejaw’s preferred depth – 1700 to 13,000 feet (500-4000 m) below the sea surface. This species likely utilizes its light organs to visually locate prey. The red organ, in particular, is valuable because most species at those depths cannot see red light. A red crustacean, for example, would be easy to see in red light, even if the crustacean cannot sense the light itself. Adult Stoplight Loosejaws are less than one foot (30 cm) long and eat small fishes and crustaceans. The Stoplight Loosejaw uses its long, needle-like teeth and unique jaws to ensure that no passing meal is too big to miss. Unlike some closely related fishes that migrate toward the surface each night, scientists believe that the Stoplight Loosejaw stays in the deep.

Like most species in the deep sea, the Stoplight Loosejaw is very difficult to study and is only known from specimens that are brought up from deep nets. Stoplight Loosejaws are not eaten by people, and there is no evidence to suggest that people have any negative affects on their populations. However, the deep sea is known to be a changing environment, so it is important for scientists to continue monitoring this large marine habitat.

Stoplight Loosejawzoom image
  • Distribution worldwide in tropical to sub-polar latitudes
  • Ecosystem/Habitat deep sea/open ocean (mesopelagic to bathypelagic)
  • Feeding Habits ambush predator
  • Conservation Status unknown but likely stable
  • Taxonomy Order Stomiiformes (dragonfishes and relatives), Family Stomiidae (barbeled dragonfishes)
Stoplight loosejaw habitat mapzoom image