Actinopterygii

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Ray-finned fish
Temporal range:
Ma[1]
Electric eelRed-bellied piranhaSockeye salmonPeacock flounderAtlantic codSpotted garYellowfin tunaSpotfin lionfishHumpback anglerfishJapanese pineconefishAmerican paddlefishStriped marlinQueen angelfishNorthern pikeSlender-spined porcupine fishLeafy seadragonWels catfishTwo-banded seabreamActinopterygii.jpg
About this image
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Superclass: Osteichthyes
Class: Actinopterygii
Klein, 1885
Subclasses

Actinopterygii (

Ancient Greek πτέρυξ (ptérux) 'wing, fins'), members of which are known as ray-finned fishes, is a class of bony fish.[2] They comprise over 50% of living vertebrate species.[3]

The ray-finned fishes are so called because their fins are webs of skin supported by bony or horny spines (rays), as opposed to the fleshy, lobed fins that characterize the class Sarcopterygii (lobe-finned fish). These actinopterygian fin rays attach directly to the proximal or basal skeletal elements, the radials, which represent the link or connection between these fins and the internal skeleton (e.g., pelvic and pectoral girdles).

By species count, actinopterygians dominate the

freshwater and marine environments from the deep sea 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 the long-bodied oarfish, at 11 m (36 ft). The vast majority of Actinopterygii (~99%) are teleosts
.

Characteristics

gonopodium
)

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.[5]

Ray-finned fishes have many different types of scales; but all

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.[6]

Ray-finned and lobe-finned fishes sometimes possesses lungs used for aerial respiration. Only bichirs retain ventrally budding lungs.[5]

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.

Reproduction

Three-spined stickleback (Gasterosteus aculeatus) 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.

Protandry, where a fish converts from male to female, is much less common than protogyny.[8]

Most families use external rather than internal fertilization.[9] Of the oviparous teleosts, most (79%) do not provide parental care.[10] 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.[10] The oldest case of viviparity in ray-finned fish is found in Middle Triassic species of Saurichthys.[11] Viviparity is relatively rare and is found in about 6% of living teleost species; male care is far more common than female care.[10][12] Male territoriality "preadapts" a species for evolving male parental care.[13][14]

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.[15]

Classification and fossil record

Evolution of ray-finned fish.png

Actinopterygii is divided into the classes

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.[16]

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

period.[19] Approximate divergence dates for the different actinopterygian clades (in millions of years, mya) are from Near et al., 2012.[17]

Vertebrates
Jawed vertebrates
Euteleostomi
Sarcopterygii
Rhipidistia
Tetrapods
Amniota

British reptiles, amphibians, and fresh-water fishes (1920) (Lacerta agilis).jpg

Phylogenetic tree of marsupials derived from retroposon data (Paucituberculata).png

Salamandra salamandra (white background).jpg

Lungfish Chinle fish Arganodus cropped cropped.png

Actinistia

Coelacanths Coelacanth flipped.png

(lobe‑fins)
Actinopterygii
Cladistia

Polypteriformes (bichirs, reedfishes) Cuvier-105-Polyptère.jpg

Actinopteri
Chondrostei

Atlantic sturgeon flipped.jpg

Neopterygii
Holostei

Lepisosteiformes (gars) Alligator gar fish (white background).jpg

Amia calva (white background).jpg

275 mya

Teleostei Common carp (white background).jpg

310 mya
360 mya
400 mya
('bony fish')

ratfish) White shark (Duane Raver).png

lampreys) Nejonöga, Iduns kokbok.jpg

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.[17]

The earliest known

Era.[17]

Chondrostei
Teleostei than their external appearance might suggest.[24]
Neopterygii
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.[25]
teleosteomorph