Argentiniformes
Encyclopedia
Argentiniformes is 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 to the suborder of marine smelts and barreleye
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 6-7 families
with almost 60 genera
and some 200 species
. 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
.
fishes. Some Argentinoidei have a 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. They have a physoclistous gas bladder
or lack it entirely; teeth are absent in almost all.
The hypaxialis 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 raker
s on the 5th ceratobranchial, which is found in other teleosts too, but not as well-developed as in the present 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 and establishing a monotypic
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 classification of the Argentiniformes is:
A fossil
family that might belong in this order are the Pattersonellidae
.
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
of ray-finned fish whose distinctness was recognized only fairly recently. In former times, they were included in the Osmeriformes
Osmeriformes
Osmeriformes is an 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 Protacanthopterygii, which also includes pike and salmon, among others...
(typical smelt and allies) as suborder Argentinoidei. That term refers only to the suborder of marine smelts and barreleye
Barreleye
Barreleyes, also known as spook fish , are small deep-sea osmeriform fish comprising the family Opisthoproctidae...
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 6-7 families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
with almost 60 genera
Genera
Genera is a commercial operating system and development environment for Lisp machines developed by Symbolics. It is essentially a fork of an earlier operating system originating on the MIT AI Lab's Lisp machines which Symbolics had used in common with LMI and Texas Instruments...
and some 200 species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
. A common name for the group is marine smelts and allies, but this is rather misleading since the "freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
" smelts of the Osmeridae also live predominantly in the ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
.
Description and ecology
Argentiniformes are smallish silvery or dark and generally bathypelagic oceanOcean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
fishes. Some Argentinoidei have a adipose fin, which is – unusually for Protacanthopterygii
Protacanthopterygii
Protacanthopterygii is a ray-finned fish taxon ranked as a superorder of the infraclass Teleostei. They inhabit both marine and freshwater habitat...
to which they belong – missing in the rest of the order. The dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
is located in the second half of the body. They have a physoclistous gas bladder
Gas bladder
The swim bladder, gas bladder, fish maw or air bladder is an internal gas-filled organ that contributes to the ability of a fish to control its buoyancy, and thus to stay at the current water depth without having to waste energy in swimming...
or lack it entirely; teeth are absent in almost all.
The hypaxialis muscle is unusually extended to forward at its upper end and attaches to the neurocranium below the spine
Vertebral column
In human anatomy, the vertebral column is a column usually consisting of 24 articulating vertebrae, and 9 fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral discs...
, 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
Coronoid process
The Coronoid process can refer to:* The coronoid process of the mandible, part of the ramus mandibulae of the mandible...
. 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
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
and gill raker
Gill raker
Gill rakers in fish are bony or cartilaginous processes that project from the branchial arch and are involved with filter feeding tiny prey. They are not to be confused with the gill filaments that compose the bony part of the gill. Rakers are usually present in two rows, projecting from both the...
s on the 5th 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 orderOrder (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
follows the discovery that they are by no means as closely related to the Osmeriformes
Osmeriformes
Osmeriformes is an 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 Protacanthopterygii, which also includes pike and salmon, among others...
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
Stenopterygii
Stenopterygii are a superorder of ray-finned fish in the infraclass Teleostei. Their validity is somewhat doubtful, as the group was established to separate, out of a large group of closely related Teleostei, a mere two rather peculiarly autapomorphic orders at best...
" in the Protacanthopterygii, or – if the unranked clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
name Euteleostei is used for this entire group – restricting the Protacanthopterygii to the Osmeriformes and either Esociformes
Esociformes
Esociformes is a small order of ray-finned fish, with two families, the Umbridae and the Esocidae . The pikes of genus Esox give the order its name. There are ten species — five in each family....
or Salmoniformes and establishing a monotypic
Monotypic
In biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...
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 classification of the Argentiniformes is:
- Suborder Alepocephaloidei
- Family AlepocephalidaeAlepocephalidaeSlickheads or nakedheads are a family, Alepocephalidae, of osmeriform fishes. They are deep-water fishes most common below 1,000 m...
– typical slickheads (including Bathylaconidae) - Family Leptochilichthyidae – aberrant slickheads
- Family PlatytroctidaePlatytroctidaeThe tubeshoulders are a family, the Platytroctidae, of marine osmeriform fishes. They are found throughout the world, except for the Mediterranean sea. Tubeshoulders live at moderate depths of to , and some have light-producing organs...
(including Searsiidae)
- Family Alepocephalidae
- Suborder Argentinoidei
- Family Argentinidae – herring smelts
- Family Bathylagidae – deep-sea smelts (sometimes included in Microstomatidae)
- Family MicrostomatidaeMicrostomatidaeMicrostomatidae is a family of osmeriform fishes.They are native to the Atlantic, Indian and Pacific Oceans.- Species :There are twenty species in three genera:* Genus Microstoma** Slender argentine, Microstoma microstoma ....
– pencil smelts - Family Opisthoproctidae – barreleyes
A fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
family that might belong in this order are the Pattersonellidae
Pattersonellidae
Pattersonellidae is a an extinct family of primitive ray-finned fish. It is tentatively classified under the suborder Argentinoidei of the order Argentiniformes ....
.