The Argentiniformes are smallish, silvery or dark and generally
bathypelagic ocean fishes. Some
Argentinoidei have an
adipose fin, which is – unusually for
Protacanthopterygii to which they belong – missing in the rest of the order. The
dorsal fin is located in the second half of the body. Teeth are absent in almost all. Suborder Argentinoidei have a
physoclistous gas bladder when present, or they lack it entirely. In suborder Alepocephaloidei the swim bladder is completely absent. The
hypaxial muscle is unusually extended to forward at its upper end and attaches to the
neurocranium below the
spine, perhaps to snap the upper part of the skull down when catching prey. The primordial ligament attaches posteriorly on the upper surface of the
coronoid process. The autopalatine is peculiarly expanded to above and below at its
caudal end, and like in some
Otocephala, the
caudal part of the mesethmoid appears compressed when seen from above. As in many other
teleosts, the autopterotic and dermopterotic bones are not fused together. The most distinctive characteristic, however, is the crumenal organ, also called epibranchial organ. This consists of the additional
cartilage and
gill rakers on the fifth ceratobranchial, which is found in other teleosts, too, but not as well-developed as in the present order. ==Systematics==