The Argentiniformes are an

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number 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 The Osmeriformes are an order (biology), order of ray-finned fish that includes the true or freshwater smelts and allies, such as the galaxiids and noodlefishes; they are also collectively called osmeriforms. They belong to the teleost superorder ...

(typical

smelt Smelt may refer to: * Smelting, chemical process * The common name of various fish: ** Smelt (fish), a family of small fish, Osmeridae ** Australian smelt in the family Retropinnidae and species ''Retropinna semoni'' ** Big-scale sand smelt ''A ...

and allies) as

suborder Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...

Argentinoidei. That term refers only to the suborder of marine smelts and barreleyes 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. Idea ...

with almost 60

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial ...

and at least 228

species In biology, a species is the basic unit of Taxonomy (biology), 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 ...

. A common name for the group is marine smelts and allies, but this is rather misleading since the "

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does in ...

" smelts of the

Osmeridae Smelts are a family of small fish, the Osmeridae, found in the North Atlantic and North Pacific Oceans, as well as rivers, streams and lakes in Europe, North America and Northeast Asia. They are also known as freshwater smelts or typical smelts ...

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 FishBase is a global species database of fish species (specifically finfish). It is the largest and most extensively accessed online database on adult finfish on the web.

(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 The bathypelagic zone or bathyal zone (from Greek βαθύς (bathýs), deep) is the part of the open ocean that extends from a depth of below the ocean surface. It lies between the mesopelagic above, and the abyssopelagic below. The bathypelag ...

ocean fishes. Some Argentinoidei 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 s ...

, 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 rou ...

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

gas bladder 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 wi ...

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 sk ...

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 Caudal may refer to: Anatomy * Caudal (anatomical term) (from Latin ''cauda''; tail), used to describe how close something is to the trailing end of an organism * Caudal artery, the portion of the dorsal aorta of a vertebrate that passes into the ...

end, and like in some

Otocephala Otocephala is a clade of ray-finned fishes within the infraclass Teleostei that evolved some 230 million years ago. It is named for the presence of a hearing (otophysic) link from the swimbladder to the inner ear. Other names proposed for the gro ...

, the

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. Tel ...

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 th ...

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

follows the discovery that they are by no means as closely related to the

as was long believed. In fact, they may actually be the most

basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is nec ...

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 The Esociformes () are a small order of ray-finned fish, with two families, Umbridae and Esocidae. The pikes of genus ''Esox'' give the order its name. This order is closely related to the Salmoniformes, the two comprising the superorder ...

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 whitefish ...

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 "unispec ...

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

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 Slickheads, also known as nakedheads or smoothheads, are deep water fishes that belong to the family Alepocephalidae. They are most commonly found in the bathypelagic layer, which is approximately 3000m below the surface. They get their name from ...

(typical slickheads) (includes Bathylaconidae; Leptochilichthyidae) ** Family

Platytroctidae The tubeshoulders are a family, Platytroctidae, of ray-finned fish belonging to the order Alepocephaliformes. They are found throughout the world, except for the Mediterranean Sea. Tubeshoulders live at moderate depths of , and some have light-p ...

(including Searsiidae) * Suborder Argentinoidei ** Family

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

(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) 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.

References

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

Description and ecology

Systematics

See also

References