Macrouroidei

Macrouroidei is a suborder of deep sea fish, a diverse and ecologically important group, which are part of the order of cod-like fish, the Gadiformes. The species in the Macrouroidei are characterised by their large heads which normally have a single barbel on the chin, projecting snouts, and slender bodies that taper to whip-like tails, without an obvious caudal fin but what there is of the caudal fin is often confluent with the posterior dorsal and anal fins. There are normally two dorsal fins, the anterior dorsal fin is quite high, the posterior quite low but is longer and takes up a greater proportion of the fish's back. A few species in the Trachyrincidae have a single dorsal fin. The long anal fin is almost as long as the posterior dorsal fin, and sometimes it is longer. The pelvic fin is inserted in the vicinity of the thorax and normally has 5–17 fin rays but these are absent in Macrouroides. The body is covered in small scales and if they have a photophore, it is usually on the midline of the abdomen just in front of the anus. The bioluminescence of these fish is produced by symbiotic bioluminescent bacteria. The structure of the skull has been used to show their placing in the Gadiformes, but they differ from the typical cods in that they possess one stout spine in the anterior dorsal fin.

The species in this suborder are mainly benthopelagic, they are found at depths of 200–2000 m, they occur on the sea bed and have a wide distribution from the Arctic to the Antarctic.