Actinopterygii (//; from actino- 'having rays', and Ancient Greek πτέρυξ (ptérux) 'wing, fins'), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webs of skin supported by radially extended bony spines, as opposed to the bulkier, fleshy lobed fins of the sister class Sarcopterygii (lobe-finned fish). Resembling folding fans, the actinopterygian fins can change shape and wetted area easily, providing superior thrust-to-weight ratios per movement compared to sarcopterygian and chondrichthyian fins. The fin rays attach directly to the proximal or basal skeletal elements, the radials, which represent the articulation between these fins and the internal skeleton (e.g., pelvic and pectoral girdles).
The vast majority (~99%) of actinopterygians are teleosts. By species count, they dominate the subphylum Vertebrata, and constitute nearly 99% of the over 30,000 extant species of fish. They are the most abundant nektonic aquatic animals and are ubiquitous throughout freshwater and marine environments from the deep sea to subterranean waters to the highest mountain streams. Extant species can range in size from Paedocypris, at 8 mm (0.3 in); to the massive ocean sunfish, at 2,300 kg (5,070 lb); and to the long-bodied oarfish, at 11 m (36 ft).
Ray-finned fishes occur in many variant forms. The main features of typical ray-finned fish are shown in the adjacent diagram. The swim bladder is a more derived structure than the lung and used for buoyancy. Except from the bichirs, which just like the Sarcopterygii (lobe-finned fish) have retained the ancestral condition of ventrally budding lungs, the swim bladder in ray-finned fishes derives from a dorsal bud above the foregut. In early forms the swim bladder could still be used for breathing, a trait still present in Holostei (bowfins and gars). In some fish, like the arapaima, the swim bladder has been modified for breathing air again, and in other lineages it have been completely lost.
Ray-finned fishes have many different types of scales; but all teleosts have leptoid scales. The outer part of these scales fan out with bony ridges, while the inner part is crossed with fibrous connective tissue. Leptoid scales are thinner and more transparent than other types of scales, and lack the hardened enamel or dentine-like layers found in the scales of many other fish. Unlike ganoid scales, which are found in non-teleost actinopterygians, new scales are added in concentric layers as the fish grows.
Body shapes and fin arrangements
Ray-finned fish vary in size and shape, in their feeding specializations, and in the number and arrangement of their ray-fins.
The swordfish is even faster and more streamlined than the tuna
The four-eyed fish Anableps anableps can see both below and above the water surface
Fangtooth are indifferent swimmers who try to ambush their prey
The first spine of the dorsal fin of anglerfish is modified like a fishing rod with a lure
European conger are ray-finned fish
In nearly all ray-finned fish, the sexes are separate, and in most species the females spawn eggs that are fertilized externally, typically with the male inseminating the eggs after they are laid. Development then proceeds with a free-swimming larval stage. However other patterns of ontogeny exist, with one of the commonest being sequential hermaphroditism. In most cases this involves protogyny, fish starting life as females and converting to males at some stage, triggered by some internal or external factor. Protandry, where a fish converts from male to female, is much less common than protogyny.
Most families use external rather than internal fertilization. Of the oviparous teleosts, most (79%) do not provide parental care. Viviparity, ovoviviparity, or some form of parental care for eggs, whether by the male, the female, or both parents is seen in a significant fraction (21%) of the 422 teleost families; no care is likely the ancestral condition. The oldest case of viviparity in ray-finned fish is found in Middle Triassic species of †Saurichthys. Viviparity is relatively rare and is found in about 6% of living teleost species; male care is far more common than female care. Male territoriality "preadapts" a species for evolving male parental care.
There are a few examples of fish that self-fertilise. The mangrove rivulus is an amphibious, simultaneous hermaphrodite, producing both eggs and spawn and having internal fertilisation. This mode of reproduction may be related to the fish's habit of spending long periods out of water in the mangrove forests it inhabits. Males are occasionally produced at temperatures below 19 °C (66 °F) and can fertilise eggs that are then spawned by the female. This maintains genetic variability in a species that is otherwise highly inbred.
Classification and fossil record
Actinopterygii is divided into the classes Cladistia and Actinopteri. The latter comprises the subclasses Chondrostei and Neopterygii. The Neopterygii, in turn, is divided into the infraclasses Holostei and Teleostei. During the Mesozoic (Triassic, Jurassic, Cretaceous) and Cenozoic the teleosts in particular diversified widely. As a result, 96% of living fish species are teleosts (40% of all fish species belong to the teleost subgroup Acanthomorpha), while all other groups of actinopterygians represent depauperate lineages.
The classification of ray-finned fishes can be summarized as follows:
- Cladistia, which include bichirs and reedfish
- Actinopteri, which include:
- Chondrostei, which include Acipenseriformes (paddlefishes and sturgeons)
- Neopterygii, which include:
- Teleostei (most living fishes)
- Holostei, which include:
- Lepisosteiformes (gars)
- Amiiformes (bowfin)
The cladogram below shows the main clades of living actinopterygians and their evolutionary relationships to other extant groups of fishes and the four-limbed vertebrates (tetrapods). The latter include mostly terrestrial species but also groups that became secondarily aquatic (e.g. Whales and Dolphins). Tetrapods evolved from a group of bony fish during the Devonian period. Approximate divergence dates for the different actinopterygian clades (in millions of years, mya) are from Near et al., 2012.
The polypterids (bichirs and reedfish) are the sister lineage of all other actinopterygians, the Acipenseriformes (sturgeons and paddlefishes) are the sister lineage of Neopterygii, and Holostei (bowfin and gars) are the sister lineage of teleosts. The Elopomorpha (eels and tarpons) appear to be the most basal teleosts.
The earliest known fossil actinopterygian is Andreolepis hedei, dating back 420 million years (Late Silurian), remains of which have been found in Russia, Sweden, and Estonia. Crown group actinopterygians most likely originated near the Devonian-Carboniferous boundary. The earliest fossil relatives of modern teleosts are from the Triassic period (Prohalecites, Pholidophorus), although it is suspected that teleosts originated already during the Paleozoic Era.
|Chondrostei||Chondrostei (cartilage bone) is a subclass of primarily cartilaginous fish showing some ossification. Earlier definitions of Chondrostei are now known to be paraphyletic, meaning that this subclass does not contain all the descendants of their common ancestor. There used to be 52 species divided among two orders, the Acipenseriformes (sturgeons and paddlefishes) and the Polypteriformes (reedfishes and bichirs). Reedfish and birchirs are now separated from the Chondrostei into their own sister lineage, the Cladistia. It is thought that the chondrosteans evolved from bony fish but lost the bony hardening of their cartilaginous skeletons, resulting in a lightening of the frame. Elderly chondrosteans show beginnings of ossification of the skeleton, suggesting that this process is delayed rather than lost in these fish. This group had once been classified with the sharks: the similarities are obvious, as not only do the chondrosteans mostly lack bone, but the structure of the jaw is more akin to that of sharks than other bony fish, and both lack scales (excluding the Polypteriforms). Additional shared features include spiracles and, in sturgeons, a heterocercal tail (the vertebrae extend into the larger lobe of the caudal fin). However the fossil record suggests that these fish have more in common with the Teleostei than their external appearance might suggest.|
|Neopterygii||Neopterygii (new fins) is a subclass of ray-finned fish that appeared somewhere in the Late Permian. There were only few changes during its evolution from the earlier actinopterygians. Neopterygians are a very successful group of fishes because they can move more rapidly than their ancestors. Their scales and skeletons began to lighten during their evolution, and their jaws became more powerful and efficient. While electroreception and the ampullae of Lorenzini is present in all other groups of fish, with the exception of hagfish, neopterygians have lost this sense, though it later re-evolved within Gymnotiformes and catfishes, who possess nonhomologous teleost ampullae.|
The listing below is a summary of all extinct (indicated by a dagger, †) and living groups of Actinopterygii with their respective taxonomic rank. The taxonomy follows Phylogenetic Classification of Bony Fishes with notes when this differs from Nelson, ITIS and FishBase and extinct groups from Van der Laan 2016 and Xu 2021.
- Order †?Asarotiformes Schaeffer 1968
- Order †?Discordichthyiformes Minikh 1998
- Order †?Paphosisciformes Grogan & Lund 2015
- Order †?Scanilepiformes Selezneya 1985
- Order †Cheirolepidiformes Kazantseva-Selezneva 1977
- Order †Paramblypteriformes Heyler 1969
- Order †Rhadinichthyiformes
- Order †Palaeonisciformes Hay 1902
- Order †Tarrasiiformes sensu Lund & Poplin 2002
- Order †Ptycholepiformes Andrews et al. 1967
- Order †Haplolepidiformes Westoll 1944
- Order †Aeduelliformes Heyler 1969
- Order †Platysomiformes Aldinger 1937
- Order †Dorypteriformes Cope 1871
- Order †Eurynotiformes Sallan & Coates 2013
- Class Cladistia Pander 1860
- Class Actinopteri Cope 1972 s.s.
- Order †Elonichthyiformes Kazantseva-Selezneva 1977
- Order †Phanerorhynchiformes
- Order †Bobasatraniiformes Berg 1940
- Order †Saurichthyiformes Aldinger 1937
- Subclass Chondrostei Müller, 1844
- Subclass Neopterygii Regan 1923 sensu Xu & Wu 2012
- Order †Pholidopleuriformes Berg 1937
- Order †Redfieldiiformes Berg 1940
- Order †Platysiagiformes Brough 1939
- Order †Polzbergiiformes Griffith 1977
- Order †Perleidiformes Berg 1937
- Order †Louwoichthyiformes Xu 2021
- Order †Peltopleuriformes Lehman 1966
- Order †Luganoiiformes Lehman 1958
- Order †Pycnodontiformes Berg 1937
- Infraclass Holostei Müller 1844
- Division Halecomorphi Cope 1872 sensu Grande & Bemis 1998
- Division Ginglymodi Cope 1871
- Clade Teleosteomorpha Arratia 2000 sensu Arratia 2013
- Order †Prohaleciteiformes Arratia 2017
- Division Aspidorhynchei Nelson, Grand & Wilson 2016
- Infraclass Teleostei Müller 1844 sensu Arratia 2013
- Order †?Araripichthyiformes
- Order †?Ligulelliiformes Taverne 2011
- Order †?Tselfatiiformes Nelson 1994
- Order †Pholidophoriformes Berg 1940
- Order †Dorsetichthyiformes Nelson, Grand & Wilson 2016
- Order †Leptolepidiformes
- Order †Crossognathiformes Taverne 1989
- Order †Ichthyodectiformes Bardeck & Sprinkle 1969
- Teleocephala de Pinna 1996 s.s.
- Megacohort Elopocephalai Patterson 1977 sensu Arratia 1999 (Elopomorpha Greenwood et al. 1966)
- Megacohort Osteoglossocephalai sensu Arratia 1999
- Supercohort Osteoglossocephala sensu Arratia 1999 (Osteoglossomorpha Greenwood et al. 1966)
- Supercohort Clupeocephala Patterson & Rosen 1977 sensu Arratia 2010
- Cohort Otomorpha Wiley & Johnson 2010 (Otocephala; Ostarioclupeomorpha)
- Subcohort Clupei Wiley & Johnson 2010 (Clupeomorpha Greenwood et al. 1966)
- Subcohort Alepocephali
- Order Alepocephaliformes Marshall 1962
- Subcohort Ostariophysi Sagemehl 1885
- Section Anotophysa (Rosen & Greenwood 1970) Sagemehl 1885
- Section Otophysa Garstang 1931
- Order Cypriniformes Bleeker 1859 sensu Goodrich 1909 (barbs, carp, danios, goldfishes, loaches, minnows, rasboras)
- Order Characiformes Goodrich 1909 (characins, pencilfishes, hatchetfishes, piranhas, tetras, dourado / golden (genus Salminus) and pacu)
- Order Gymnotiformes Berg 1940 (electric eels and knifefishes)
- Order Siluriformes Cuvier 1817 sensu Hay 1929 (catfishes)
- Cohort Euteleosteomorpha (Greenwood et al. 1966) (Euteleostei Greenwood 1967 sensu Johnson & Patterson 1996)
- Subcohort Lepidogalaxii
- Subcohort Protacanthopterygii Greenwood et al. 1966 sensu Johnson & Patterson 1996
- Subcohort Stomiati
- Subcohort Neoteleostei Nelson 1969
- Infracohort Ateleopodia
- Infracohort Eurypterygia Rosen 1973
- Section Aulopa [Cyclosquamata Rosen 1973]
- Section Ctenosquamata Rosen 1973
- Subsection Myctophata [Scopelomorpha]
- Subsection Acanthomorpha Betancur-Rodriguez et al. 2013
- Division Lampridacea Betancur-Rodriguez et al. 2013 [Lampridomorpha; Lampripterygii]
- Division Paracanthomorphacea sensu Grande et al. 2013 (Paracanthopterygii Greenwood 1937)
- Division Polymixiacea Betancur-Rodriguez et al. 2013 (Polymyxiomorpha; Polymixiipterygii)
- Division Euacanthomorphacea Betancur-Rodriguez et al. 2013 (Euacanthomorpha sensu Johnson & Patterson 1993; Acanthopterygii Gouan 1770 sensu])
- Subdivision Berycimorphaceae Betancur-Rodriguez et al. 2013
- Subdivision Holocentrimorphaceae Betancur-Rodriguez et al. 2013
- Subdivision Percomorphaceae Betancur-Rodriguez et al. 2013 (Percomorpha sensu Miya et al. 2003; Acanthopteri)
- Series Ophidiimopharia Betancur-Rodriguez et al. 2013
- Series Batrachoidimopharia Betancur-Rodriguez et al. 2013
- Series Gobiomopharia Betancur-Rodriguez et al. 2013
- Series Scombrimopharia Betancur-Rodriguez et al. 2013
- Series Carangimopharia Betancur-Rodriguez et al. 2013
- Subseries Anabantaria Betancur-Rodriguez et al. 2014
- Subseries Carangaria Betancur-Rodriguez et al. 2014
- Subseries Ovalentaria Smith & Near 2012 (Stiassnyiformes sensu Li et al. 2009)
- Ovalentaria incertae sedis
- Order Cichliformes Betancur-Rodriguez et al. 2013 (Cichlids, Convict blenny, leaf fishes)
- Order Atheriniformes Rosen 1964 (silversides and rainbowfishes)
- Order Cyprinodontiformes Berg 1940 (livebearers, killifishes)
- Order Beloniformes Berg 1940 (flyingfishes and ricefishes)
- Order Mugiliformes Berg 1940 (mullets)
- Order Blenniiformes Springer 1993 (Blennies)
- Order Gobiesociformes Gill 1872 (Clingfishes)
- Series Eupercaria Betancur-Rodriguez et al. 2014 (Percomorpharia Betancur-Rodriguez et al. 2013)
- Eupercaria incertae sedis
- Order Gerreiformes (Mojarras)
- Order Labriformes (Wrasses and Parrotfishes)
- Order Caproiformes (Boarfishes)
- Order Lophiiformes Garman 1899 (Anglerfishes)
- Order Tetraodontiformes Regan 1929 (Filefishes and pufferfish)
- Order Centrarchiformes Bleeker 1859 (Sunfishes and mandarin fishes)
- Order Gasterosteiformes (Sticklebacks and relatives)
- Order Scorpaeniformes (Lionfishes and relatives)
- Order Perciformes Bleeker 1859
- Cohort Otomorpha Wiley & Johnson 2010 (Otocephala; Ostarioclupeomorpha)
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