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 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 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.
- Family Euclichthyidae <small>Cohen, 1984</small> (Eucla cods)
- Family Muraenolepididae <small>Regan, 1903</small> (eel cods)
- Family Melanonidae <small>Goode & Bean, 1896</small> (arrowtails or pelagic cods)
- Family Trachyrincidae <small>Goode & Bean, 1896</small> (armoured grenadiers)
- Family Moridae <small>Moreau, 1881</small> (codlings or deepsea cods)
- Family Macruronidae <small>Regan, 1903</small> (blue grenadiers)
- Family Lyconidae <small>Günther, 1887</small> (Atlantic hakes)
- Family Bathygadidae <small>Jordan & Evermann, 1898</small> (rattails)
- Family Steindachneriidae <small>Parr, 1942</small> (luminous hakes)
- Family Macrouridae <small>Bonaparte, 1831</small> (grenadiers or rattails)
The earliest known genus is Bobbitichthys <small>Schwarzhans, Milàn & Carnevale, 2021</small>, a stem-macrourid from the middle Paleocene of Denmark. A well-preserved skull of an indeterminate macrourid is known from the Eocene-aged La Meseta Formation of Antarctica. The extinct genus Bolbocara <small>Jordan, 1927</small> is known from an articulated fossil skeleton from the Late Miocene of California, while Razelaina <small>Carnevale, 2007</small> is known from the Late Miocene of Algeria.