''Malacosteus australis'', the southern stoplight loosejaw, is a species of

barbeled dragonfish Stomiidae is a family (biology), family of deep-sea ray-finned fish, including the barbeled dragonfishes, that live in all oceans in a wide range of depths. They are quite small, usually around 15 cm, up to 26 cm, and they exhibit a st ...

. This species is mainly distinguished from ''

Malacosteus niger ''Malacosteus niger'', commonly known as the stoplight loosejaw, is a species of deep-sea fish. Some additional common names for this species include: northern stoplight loosejaw, lightless loosejaw, black loosejaw, and black hinged-head.Harold, ...

'' by a smaller postorbital

photophore A photophore is a specialized anatomical structure found in a variety of organisms that emits light through the process of boluminescence. This light may be produced endogenously by the organism itself (symbiotic) or generated through a mut ...

in both sexes and lower numbers of lateral photophores. It also differs in having somewhat smaller jaws, a fleshy

orbit In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an ...

, and several subtle morphological traits. The maximum known length is 253.2 mm. Its

specific epithet In Taxonomy (biology), taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin gramm ...

comes from the

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

''austral'', meaning "southern". It is known for its red bioluminescence which helps ''M. australis'' visualize in the

aphotic The aphotic zone (aphotic from Greek prefix + "without light") is the portion of a lake or ocean where there is little or no sunlight. It is formally defined as the depths beyond which less than 1 percent of sunlight penetrates. Above the aphot ...

deep sea The deep sea is broadly defined as the ocean depth where light begins to fade, at an approximate depth of or the point of transition from continental shelves to continental slopes. Conditions within the deep sea are a combination of low tempe ...

Description

''Malacosteus australis'' have long bodies with large eyes. The blunt and short snout has a single round nostril. This species has barbed, curved, knife-shaped teeth. They have thin, scaleless, black skin.

Red light physiological adaptation

''Malacosteus australis,'' along with three of the four loosejaw genera (''Malacosteus, Pachystomias,'' and ''Aristostomias)'' have an adaptation to their accessory orbital photophore. ''Malacosteus'' have a large single tear-dropped size accessory light organ. Blue light travels furthest in the ocean, so because of this, most organisms have eyes adjusted to see blues and greens clearly, but cannot detect other colors very well or at all. This adaptation to the loosejaw genera allow these organisms to have red-light bioluminescence. An emission maxima above 515 (such as the ''M. australis'''s red light) is very rare. In the mesopelagic region, this red light is undetectable visually to all the other fish. ''Malacosteus'' uses a bacteriochlorophyll-based photosensitizer to be able to see long wavelengths.

References

* Stomiidae Fish described in 2007 {{Stomiiformes-stub