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Visual System
Malacosteus niger has yellow lenses that are believed to improve the functionality of the perception of their red bioluminescence. M. niger adapted a retinal structure of "ten later elements," similar to those found in surface-level species and other shallow-water living species — which also perceive red light. Its retina is made up entirely of rods and no cones, with rhodopsin/porphyropsin pairs and a single opsin bound to some of its photoreceptors, which provide visual sensitivity up to 517-541 nm. For comparison, other red light producing stomiids, such as Aristostomias and Pachystostomias, have a third pigment which allows them to perceive light up to 588 nm and 595 nm respectively. The yellow lens reduce the amount of blue light that reaches the retina and increases sensitivity to longer wavelengths, which benefits M. niger and its red bioluminescence.

Yellow lens have also been identified in Echiostoma, which also produces red bioluminescence.

Morphology
M. niger is unique from other stomiid genera because its jaw is over 30% its whole body length (average around 4.5 mm), which aids in catching larger prey. Its jaw is also made up of large, fang-like teeth, its lower-jaw lacks a floor to the oral cavity, and it can open its jaw greater than 120˚. The lack of a floor of to the oral cavity allows for decreased resistive forces which allows M. niger to close its mouth rapidly and easily trap its prey. This adaptation also minimizes the amount of energy required for M. niger to close its mouth, thus permitting it to quickly latch onto fast-swimming prey.

Ecological and Geographical Distribution
Malacosteus niger has been documented inhabiting the North Atlantic, the Gulf of Mexico, and throughout the Pacific Ocean. Unlike other mesopelagic fish, M. niger does not participate in diel vertical migration, thus its vertical distribution falls within the mesopelagic zone (500 m - 1000 m).

Diet
M. niger is an apex predator and a piscivore. Due to the small biomass present in its ecosystems, M. niger consumes a considerable amount of copepods to fulfill its energy requirements between meals. Its documented prey include calanoid copepods, micronekton, decapod shrimps, and other decapods. M. niger digests its prey within a diel cycle, meaning the copepods it consumes at nighttime are digested by the afternoon the following day, which requires it to be constantly feeding on these small prey to sustain its energy; copepods make up 69-83% of its diet.

Red Bioluminescence
M niger 's unique adaptation of producing red bioluminescence is only found in two other deep-sea dwelling creatures, Aristostomias and Pachystomias. This rare form of bioluminescence can reach up to 700 nm in the deep-sea and cannot be perceived by green and blue bioluminescent organisms, thus granting M. niger a considerable advantage while hunting for food.