Actinopterygii

Actinopterygii /ˌæktᵻnˌɒptəˈrɪdʒi.aɪ/, or the ray-finned fishes, constitute a class of the bony fishes.

The ray-finned fishes earned their common name as they possess lepidotrichia, or webbed skin supported by bony, horn-like spines, known colloquially as "rays"; this is in contrast to the fleshy, lobed fins that characterize the class Sarcopterygii, which, ironically, also possess lepidotrichia. The actinopterygians' fin rays attach directly to the proximal or basal skeletal elements, the radials, which represent the link or connection between the fins and the internal skeleton (e.g., pelvic and pectoral girdles).

Numerically, actinopterygians are a dominant class of vertebrates, comprising nearly 99% of the 30,000+ fish species.^[1] They are ubiquitous throughout freshwater and marine environments, ranging from the deepest oceans to the coldest, highest mountain streams. Extant species can range in size from Paedocypris, at 8 mm (0.3 in), to the massive ocean sunfish (Mola mola), which weighs in at 2,300 kg (5,070 lbs), or the long-bodied, deep-diving oarfish, measuring some 11 m (36 ft) long.

Characteristics[]

Anatomy of a typical ray-finned fish.

A – dorsal fin: B – fin rays: C – lateral line: D – kidney: E – swim bladder: F – Weberian apparatus: G – inner ear: H – brain: I – nostrils: L – eye: M – gills: N – heart O – stomach: P – gall bladder: Q – spleen: R – internal sex organs (ovaries or testes): S – ventral fins: T – spine: U – anal fin: V – tail (caudal fin). Possible other parts not shown: barbels, adipose fin, external genitalia (gonopodium)

Ray-finned fishes occur in many variant forms. The main features of a typical ray-finned fish are shown in the diagram at the left.

Fin arrangements
Ray-finned fish are varied in size, shape and the arrangement and number of their ray-fins. See fish fin. Tuna are streamlined for straight line speed with a deeply forked tail The swordfish is even faster and more streamlined than the tuna Salmon generate enough thrust with their powerful tail fin to jump obstacles during river migrations Cod have three dorsal and two anal fins, which give them great maneuverability Catfish Flatfish have developed partially symmetric dorsaland pelvic fins Sturgeon Lanternfish Elongated bristlemouth Fangtooth are indifferent swimmer who try to ambush their prey The first spine of the dorsal fin of anglerfish is modified like a fishing rod with a lure Alfonsino King of herrings Cutlassfish European conger are ray-finned fish So are sea horses White Siamese fighting fish Mirror dory The venomous lion fish Tiger fish

ReproductionEdit[]

Three-spined stickleback males (red belly) build nests and compete to attract females to lay eggs in them. Males then defend and fan the eggs. Painting by Alexander Francis Lydon, 1879

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 transitioning to males at some stage, triggered by some internal or external factor. This may be advantageous as females become less prolific as they age while male fecundity increases with age. Protandry, where a fish transitions 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. Viviparity is relatively rare and is found in about 6% of 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.

Fossil record[]

Evolution of fish[]

The earliest known fossil actinopterygiian is Andreolepis hedei, dating back 420 million years (Late Silurian). Remains have been found in Russia, Sweden, and Estonia.

Classification[]

Actinopterygians are divided into the subclasses Chondrostei and Neopterygii. The Neopterygii, in turn, are divided into the infraclasses Holostei and Teleostei. During the Mesozoic and Cenozoic the teleosts in particular diversified widely, and as a result, 96% of all known fish species are teleosts. The cladogram shows the major groups of actinopterygians and their relationship to the terrestrial vertebrates (tetrapods) that evolved from a related group of fish. Approximate dates are from Near et al., 2012.

Osteichthyes

Actinopterygii 400 mya

Chondrostei (sturgeons, paddlefishes, reedfishes, bichirs)

Neopterygii 360 mya

	Holostei (bowfins, gars) 275 mya

	Teleostei 310 mya

Sarcopterygii

Coelacanths, Lungfish

Tetrapods

Amphibians

Amniota

	Mammals

	Sauropsids (reptiles, birds)

The polypterids (bichirs and ropefish) 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) appears to be the most basic teleosts.

Chondrostei	White Sturgeon	Chondrostei (cartilage bone) are primarily cartilaginous fish showing some ossification. There are 52 species divided among two orders, the Acipenseriformes (sturgeons and paddlefishes) and the Polypteriformes (reedfishes and bichirs). 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.^[14] This group has at times 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.^[14] Chondrostei is paraphyletic meaning that this subclass does not contain all the descendants of their common ancestor; reclassification of the Chondrostei is therefore not out of the question.
Neopterygii	Sockeye Salmon	Neopterygii (new fins) appeared somewhere in the Late Permian, before the time of the dinosaurs. There are only few changes during their evolution from the earlier actinopterygians. They 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, Neopterygii has lost this sense, though it later re-evolved within Gymnotiformes and catfishes, who possess nonhomologous teleost ampullae.^[15]

Skeleton of the angler fish, Lophius piscatorius. The first spine of the dorsal fin of the anglerfish is modified so it functions like a fishing rod with a lure

Skeleton of another ray-finned fish, the lingcod

Hypsospondylus fossil

The listing below follows Phylogenetic Classification of Bony Fishes ^[16] with notes when this differs from Nelson,^[17] ITIS ^[18] and FishBase.^[19]

Subclass Cladistii Pander 1860
- Order †Guildayichthyiformes Lund 2000
- Order Polypteriformes (bichirs and reedfishes) ^[20]
Subclass Actinopteri Cope 1972
- Order †Tarrasiiformes
- Order †Cheirolepidiformes
- Order †Paramblypteriformes Heyler 1969
- Order †Rhadinichthyiformes
- Order †Phanerorhynchiformes
- Order †Luganoiiformes Lehman 1958
- Order †Haplolepidiformes
- Order †Ptycholepiformes
- Order †Platysomiformes
- Order †Palaeonisciformes
- Order †Pholidopleuriformes
- Order †Peltopleuriformes
- Order †Perleidiformes
- Infra class Chondrostei
  - Order Acipenseriformes (sturgeons and paddlefishes)
  - Order †Saurichthyiformes
- Infra class Neopterygii Regan 1923
  - Order †Pachycormiformes
  - Holostei
    - Order †Parasemionotiformes Lehman 1966
    - Order †Ionoscopiformes Grande & Bemis 1998
    - Order †Pycnodontiformes Berg 1937
    - Order †Semionotiformes Arambourg & Bertin 1958
    - Order Lepisosteiformes (gars)
    - Order Amiiformes (bowfins)
  - Teleostei Müller 1844
    - Aspidorhynchiformes
    - Pholidophoriformes
    - Leptolepidiformes
    - Teleocephala
      - Megacohort Elopocephalai Patterson 1977 sensu Arratia 1999 (Elopomorpha Greenwood et al. 1966)
        Order Elopiformes (ladyfishes and tarpon)
        
        Order Albuliformes (bonefishes)
        
        Order Notacanthiformes (halosaurs and spiny eels)
        
        Order Anguilliformes Regan 190 (true eels)
      - Megacohort Osteoglossocephalai sensu Arratia 1999
        Supercohort Osteoglossocephala sensu Arratia 1999 (Osteoglossomorpha Greenwood et al. 1966)
        Order †Ichthyodectiformes Bardeck & Sprinkle 1969
        
        Order †Lycopteriformes
        
        Order Osteoglossiformes (bony-tongued fishes)
        
        Order Hiodontiformes (mooneye and goldeye)
        
        Supercohort Clupeocephala Patterson & Rosen 1977 sensu Arratia 2010
        Order †Crossognathiformes Taverne 1989
        
        Order †Tselfatiiformes Nelson 1994
        
        Cohort Otomorpha (Otocephala; Ostarioclupeomorpha)
        Subcohort Clupei (Clupeomorpha)
        Order †Ellimmichthyiformes Grande 1982
        
        Order Clupeiformes (herrings and anchovies)
        
        Subcohort Alepocephali
        Order Alepocephaliformes
        
        Subcohort Ostariophysi Sagemehl 1885
        Section Anotophysa Rosen 1970
        Order Gonorynchiformes (milkfishes)
        
        Section Otophysa Garstang 1931
        Order Cypriniformes (barbs, carp, danios, goldfishes, loaches, minnows, rasboras)
        
        Order Characiformes (characins, pencilfishes, hatchetfishes, piranhas, tetras, dourado / golden (genus Salminus) and pacu)
        
        Order Gymnotiformes (electric eels and knifefishes)
        
        Order Siluriformes (catfishes)
        
        Cohort Euteleosteomorpha (Euteleostei Greenwood 1967 sensu Johnson & Patterson 1996)
        Subcohort Lepidogalaxii
        Lepidogalaxiiformes
        
        Subcohort Protacanthopterygii sensu Johnson & Patterson 1996
        Order Argentiniformes (barreleyes and slickheads) (formerly in Osmeriformes)
        
        Order Galaxiiformes
        
        Order Salmoniformes (salmon and trout)
        
        Order Esociformes (pike)
        
        Subcohort Stomiati
        Order Osmeriformes (smelts)
        
        Order Stomiatiformes (bristlemouths and marine hatchetfishes)
        
        Subcohort Neoteleostei Nelson 1969
        Infracohort Ateleopodia
        Order Ateleopodiformes (jellynose fish)
        
        Infracohort Eurypterygia Rosen 1973
        Section Aulopa [Cyclosquamata]
        Order Aulopiformes (Bombay duck and lancetfishes)
        
        Section Ctenosquamata Rosen 1973
        Subsection Myctophata [Scopelomorpha]
        Order Myctophiformes (lanternfishes)
        
        Subsection Acanthomorphata
        Division Lampridacea [Lampridiomorpha]
        Order Lampriformes (oarfish, opah and ribbonfishes)
        
        Division Paracanthomorphacea sensu Grande et al. 2013 (Paracanthopterygii Greenwood 1937)
        Order Percopsiformes (cavefishes and trout-perches)
        
        Order †Sphenocephaliformes
        
        Order Zeiformes (dories)
        
        Order Stylephoriformes
        
        Order Gadiformes (cods)
        
        Division Polymixiacea (Polymyxiomorpha)
        Order †Pattersonichtyiformes
        
        Order †Ctenothrissiformes
        
        Order Polymixiiformes (beardfishes)
        
        Division Euacanthomorphacea sensu Johnson & Patterson 1993 (Acanthopterygii Gouan 1770 sensu Nelson 1994)
        Subdivision Berycimorphaceae
        Order Beryciformes (fangtooths and pineconefishes) (incl. Stephanoberyciformes; Cetomimiformes)
        
        Subdivision Holocentrimorphaceae
        Order Holocentriformes
        
        Subdivision Percomorphaceae (Percomorpha sensu Miya et al. 2003; Acanthopteri)
        Series Ophidiimopharia
        Order Ophidiiformes (pearlfishes)
        
        Series Batrachoidimopharia
        Order Batrachoidiformes (toadfishes)
        
        Series Gobiomopharia
        Order Kurtiformes
        
        Order Gobiiformes
        
        Series Scombrimopharia
        Order Syngnathiformes (seahorses and pipefishes^[21])
        
        Order Scombriformes
        
        Series Carangimopharia
        Sub Series Anabantaria
        Order Synbranchiformes (swamp eels)
        
        Order Anabantiformes (Labyrinthici)
        
        Sub Series Carangaria
        Carangaria incertae sedis
        
        Order Istiophoriformes
        
        Order Carangiformes
        
        Order Pleuronectiformes (flatfishes)
        
        Sub Series Ovalentaria sensu Smith & Near 2012 (Stiassnyiformes sensu Li et al. 2009)
        Ovalentaria incertae sedis
        
        Order Pholidichthyiformes
        
        Order Cichliformes
        
        Order Atheriniformes (silversides and rainbowfishes)
        
        Order Cyprinodontiformes (livebearers, killifishes)
        
        Order Beloniformes (flyingfishes)
        
        Order Mugiliformes (mullets)
        
        Order Blenniiformes [incl. Gobiesociformes ^[22]]
        
        Series Eupercaria (Percomorpharia)
        Eupercaria incertae sedis
        
        Order Labriformes
        
        Order Ephippiformes
        
        Order Lobotiformes
        
        Order Acanthuriformes
        
        Order Chaetodontiformes
        
        Order Spariformes
        
        Order Lophiiformes (anglerfishes)
        
        Order Tetraodontiformes (filefishes and pufferfish)
        
        Order Uranoscopiformes (Paratrachinoidei sensu Li et al. 2009)
        
        Order Pempheriformes
        
        Order Centrarchiformes
        
        Order Perciformes (incl. Gasterosteiformes; Scorpaeniformes)