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Argentinoidei

(Suborder)

Overview

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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 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 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.1]

Description and ecology

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Argentiniformes are smallish silvery or dark and generally bathypelagic 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.[2]

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 rakers on the 5th ceratobranchial, which is found in other teleosts too, but not as well-developed as in the present order.[3]

Systematics

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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 and establishing a monotypic superorder for the other of t he two latter orders. Given the reluctance of modern zoologists to establish monotypic taxa if not absolutely necessary, the former treatment is probably preferable.[4]

The classification of the Argentiniformes is:[5]

Opisthoproctus soleatus
(Argentinoidea: Opisthoproctidae)

A fossil family that might belong in this order are the Pattersonellidae.[6]

Footnotes

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  1. ^ FishBase (2006), Nelson (2006): p.190, Wikispecies (2007-FEB-05), Diogo (2008)
  2. ^ Nelson (2006): pp.190-194
  3. ^ Nelson (2006): pp.190-194, Diogo (2008)
  4. ^ Diogo (2008)
  5. ^ FishBase (2006), Nelson (2 006): pp.190-194, Diogo (2008)
  6. ^ Nelson (2006): p.190
b>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 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 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.1]

Description and ecology

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Argentiniformes are smallish silvery or dark and generally bathypelagic 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.[2]

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 teleo sts, 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 5th ceratobranchial, which is found in other teleosts too, but not as well-developed as in the present order.[3]

Systematics

[ Back to top ]

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 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.[4]

The classification of the Argentiniformes is:[5]

Opisthoproctus soleatus
(Argentinoidea: Opisthoproctidae)

A fossil family that might belong in this order are the Pattersonellidae.[6]

Footnotes

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  1. ^ FishBase (2006), Nelson (2006): p.190, Wikispecies (2007-FEB-05), Diogo (2008)
  2. ^ Nelson (2006): pp.190-194
  3. ^ Nelson (2006): pp.190-194, Diogo (2008)
  4. ^ Diogo (2008)
    5. ^ FishBase (2006), Nelson (2006): pp.190-194, Diogo (2008)
  5. ^ Nelson (2006): p.190

References

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Taxonomy

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The Suborder Argentinoidei is a member of the Order Salmoniformes. Here is the complete "parentage" of Argentinoidei:

The Suborder Argentinoidei is further organized into finer groupings including:

Families

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Alepocephalidae

Slickheads or nakedheads are a family, Alepocephalidae, of marine smelts. They are deep-water fishes most common below 1,000 metres (3,300 ft). They get their name from the lack of scales on the head. Some authors include Bathylaconidae in this family. [more]

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. [more]

Bathylagidae

The deep-sea smelts are a family, Bathylagidae, of marine smelts. [more]

Leptochilichthyidae

Leptochilichthys is a genus of marine smelts containing four species. Leptochilichthys is the only genus in the family Leptochilichthyidae. Some sources place this genus within the broader family Alepocephalidae. [more]

Microstomatidae

Microstomatidae is a family of marine smelts native to the Atlantic, Indian and Pacific Oceans. [more]

Opisthoproctidae

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

Platytroctidae

The tubeshoulders are a family, the Platytroctidae, of marine smelts. They are found throughout the world, except for the Mediterranean sea. Tubeshoulders live at moderate depths of 300 to 1,000 metres (980 to 3,300 ft), and some have light-producing organs. They are generally small to medium fish, ranging from 9 to 33 centimetres (3.5 to 13 in) in length. [more]

At least 31 species and subspecies belong to the Family Platytroctidae.

More info about the Family Platytroctidae may be found here.

References

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Sources

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Last Revised: August 24, 2012
2012/08/24 13:16:17