The Argentiniformes are an order of

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species. The ray-finned fishes are so called because their fins are webs of skin supported by bony or h ...

whose distinctness was recognized only fairly recently. In former times, they were included in the Osmeriformes (typical smelt and allies) as suborder Argentinoidei. That term refers only to the suborder of marine smelts and

barreleye Barreleyes, also known as spook fish (a name also applied to several species of chimaera), are small deep-sea argentiniform fish comprising the family Opisthoproctidae found in tropical-to-temperate waters of the Atlantic, Pacific, and I ...

s in the classification used here, with the slickheads and allies being the Alepocephaloidei. These suborders were treated as superfamilies Argentinoidea and Alepocephaloidea, respectively, when the present group was still included in the Osmeriformes. They contain six or seven

families Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideal ...

with almost 60 genera and at least 228

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

. A common name for the group is marine smelts and allies, but this is rather misleading since the " freshwater" smelts of the Osmeridae also live predominantly in the

ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...

. FishBase (2006)
Order Osmeriformes
Version of 2006-OCT-09. Retrieved 2009-SEP-28. pp. 190-194

Description and ecology

The Argentiniformes are smallish silvery or dark and generally bathypelagic ocean fishes. Some

Argentinoidei The Argentiniformes are an order of ray-finned fish whose distinctness was recognized only fairly recently. In former times, they were included in the Osmeriformes (typical smelt and allies) as suborder Argentinoidei. That term refers only t ...

have an

adipose fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

, which is – unusually for

Protacanthopterygii Protacanthopterygii is a ray-finned fish taxon ranked as a superorder of the infraclass Teleostei. They inhabit both marine and freshwater habitats. They appear to have evolved in the Cretaceous or perhaps late Jurassic, originating probably roug ...

to which they belong – missing in the rest of the order. The

dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through c ...

is located in the second half of the body. They have a

physoclistous The swim bladder, gas bladder, fish maw, or air bladder is an internal gas-filled organ that contributes to the ability of many bony fish (but not cartilaginous fish) to control their buoyancy, and thus to stay at their current water depth wit ...

gas bladder or lack it entirely; teeth are absent in almost all. The hypaxial muscle is unusually extended to forward at its upper end and attaches to the

neurocranium In human anatomy, the neurocranium, also known as the braincase, brainpan, or brain-pan is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calvaria or skul ...

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

teleost Teleostei (; Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts ), is, by far, the largest infraclass in the class Actinopterygii, the ray-finned fishes, containing 96% of all extant species of fish. Tele ...

s, 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 raker Gill rakers in fish are bony or cartilaginous processes that project from the branchial arch (gill arch) and are involved with suspension feeding tiny prey. They are not to be confused with the gill filaments that compose the fleshy part of the ...

s on the fifth ceratobranchial, which is found in other teleosts, too, but not as well-developed as in the present order.

Systematics

The treatment of the Argentiniformes as distinct order follows the discovery that they are by no means as closely related to the Osmeriformes as was long believed. In fact, they may actually be the most basal lineage of the living Protacanthopterygii. If this is so, it would probably require either inclusion of the supposed superorders " Cyclosquamata" and " Stenopterygii" in the Protacanthopterygii, or if the unranked clade name Euteleostei is used for this entire group restricting the Protacanthopterygii to the Osmeriformes and either Esociformes or

Salmoniformes Salmonidae is a family of ray-finned fish that constitutes the only currently extant family in the order Salmoniformes . It includes salmon (both Atlantic and Pacific species), trout (both ocean-going and landlocked), chars, freshwater whitefis ...

and establishing a

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispe ...

superorder for the other of the two latter orders. Given the reluctance of modern zoologists to establish monotypic taxa if not absolutely necessary, the former treatment is probably preferable. The former classification of the Argentiniformes is: * Suborder Alepocephaloidei (moved to the cohort Otocephala as AlepocephaliformesR. Betancur-Rodriguez, E. Wiley, N. Bailly, A. Acero, M. Miya, G. Lecointre, G. Ortí
''Phylogenetic Classification of Bony Fishes – Version 4''
(2016)) ** Family Alepocephalidae (typical slickheads) (includes Bathylaconidae; Leptochilichthyidae) ** Family Platytroctidae (including Searsiidae) * Suborder

** Family

Argentinidae The herring smelts or argentines are a family, Argentinidae, of marine smelts. They are similar in appearance to smelt (fish), smelts (family Smelt (fish), Osmeridae) but have much smaller mouths. They are found in oceans throughout the world. ...

(herring smelts) ** Family

Bathylagidae The deep-sea smelts are any members of the family Bathylagidae, a distinct group of marine smelts. Deep-sea smelts are marine fishes found in deep waters throughout the oceans, down to in depth. They are small fishes, growing up to long. They ...

(deep-sea smelts) ** Family Microstomatidae (pencil smelts) ** Family

Opisthoproctidae Barreleyes, also known as spook fish (a name also applied to several species of chimaera), are small deep-sea argentiniform fish comprising the family Opisthoproctidae found in tropical-to-temperate waters of the Atlantic, Pacific, and Indian ...

(barreleyes) A

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

family that might belong in this order are the

Pattersonellidae Pattersonellidae is an extinct family of primitive ray-finned fish. It is tentatively classified under the suborder Argentinoidei of the order Argentiniformes (marine smelts and allies). The family was established by Louis Taverne in 1982 wh ...

References

{{Taxonbar, from=Q1137485 Ray-finned fish orders

Description and ecology

Systematics

See also

References