[1] Malacosteus has an elongated body with short, blunt snouts and large eyes that face forward, granting binocular vision.

In addition, there are small photophores and accessory areas of white luminous tissue scattered over the head and body.

The "open" structure of its jaws allows the fish to swing its entire head forward to grab prey from afar in addition to reducing water resistance, allowing them to be snapped shut more quickly, while large recurved teeth and powerful jaw muscles assure a secure hold.

The connection between the head and the body is reduced, with unossified vertebrae, allowing the cranium to be tilted back and the jaws thrust forward for a wider gape.

Finally, the gills are exposed to the outside, allowing the fish to continue respiring while slowly swallowing large prey.

[6] However, contrary to its apparent morphological specialization, the diet of Malacosteus consists primarily of zooplankton, chiefly large calanoid copepods, with smaller numbers of krill, shrimps, and fishes.

[5] The unexpected diet of Malacosteus is theorized to be a result of the small volumes that it searches for food, in which large prey items are rare.

[7] The red photophore of Malacosteus consists of a pigmented sac with a reflective inner lining and an internal mass of gland cells.

Inside the gland cells, blue-green light is produced via the same chemical reaction found in other stomiids, which is then absorbed by a protein that fluoresces in a broad red band.