Actinopterygii

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Ray-finned fish
Temporal range:
Late SilurianPresent, 425–0 Ma[1]
Actinopterygii-0001.jpg
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Superclass: Osteichthyes
Class: Actinopterygii
Klein, 1885
Subclasses

Actinopterygii (/ˌæktɪnɒptəˈrɪi/; from actino- 'having rays', and Ancient Greek πτέρυξ (ptérux) 'wing, fins'), members of which are known as ray-finned fishes, is a clade (traditionally class or subclass) of the bony fishes.[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 vertebrates, and they comprise nearly 99% of the over 30,000 species of fish.[4] They are ubiquitous throughout 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[edit]

Anatomy of a typical ray-finned fish (cichlid)
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 adjacent diagram. The swim bladder is the more derived structure.[5]

Ray-finned fishes have many different types of scales; but all teleosts, the most advanced actinopterygians, 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.[6]

Ray-finned and lobe-finned fishes, including tetrapods, possessed lungs used for aerial respiration. Only bichirs retain ventrally budding lungs.[5]

Body shapes and fin arrangements[edit]

Ray-finned fish vary in size and shape, in their feeding specializations, and in the number and arrangement of their ray-fins.

Reproduction[edit]

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.[7] 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.[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[edit]

Evolution of ray-finned fish.png

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.[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 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).[17][18] 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.[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

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

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

Amphibians Salamandra salamandra (white background).jpg

Lungfish Barramunda coloured.jpg

Actinistia

Coelacanths Coelacanth flipped.png

(lobe‑fins)
Actinopterygii
Cladistia

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

Actinopteri
Chondrostei

Acipenseriformes (sturgeons, paddlefishes) Atlantic sturgeon flipped.jpg

Neopterygii
Holostei

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

Amiiformes (bowfins) Amia calva (white background).jpg

275 mya

Teleostei Common carp (white background).jpg

310 mya
360 mya
400 mya
('bony fish')

Cartilaginous fishes (sharks, rays, ratfish) White shark (Duane Raver).png

Jaw-less fishes (hagfish, 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 fossil actinopterygian is Andreolepis hedei, dating back 420 million years (Late Silurian). Remains have been found in Russia, Sweden, and Estonia.[20] The earliest fossil relatives of modern teleosts are from the Triassic period (Prohalecites, Pholidophorus),[21][22] although it is suspected that teleosts originated already during the Paleozoic Era.[17]

Chondrostei Atlantic sturgeon flipped.jpg
Atlantic sturgeon
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 were 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.[23] 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.[23]
Neopterygii Salmo salar flipped.jpg
Atlantic salmon
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.[24]
Fossils of the Triassic prohaleciteiform Prohalecites sp., the earliest teleosteomorph
Fossil of a ray-finned perch (Priscacara serrata) from the Lower Eocene about 50 million years ago
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
Blue catfish skeleton

Taxonomy[edit]

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[18][25] with notes when this differs from Nelson,[3] ITIS[26] and FishBase[27] and extinct groups from Van der Laan 2016[28] and Xu 2021.[29]

References[edit]

  1. ^ Zhao, W.; Zhang, X.; Jia, G.; Shen, Y.; Zhu, M. (2021). "The Silurian-Devonian boundary in East Yunnan (South China) and the minimum constraint for the lungfish-tetrapod split". Science China Earth Sciences. 64 (10): 1784–1797. Bibcode:2021ScChD..64.1784Z. doi:10.1007/s11430-020-9794-8. S2CID 236438229.
  2. ^ Kardong, Kenneth (2015). Vertebrates: Comparative Anatomy, Function, Evolution. New York: McGraw-Hill Education. pp. 99–100. ISBN 978-0-07-802302-6.
  3. ^ a b Nelson, Joseph S. (2016). Fishes of the World. John Wiley & Sons. ISBN 978-1-118-34233-6.
  4. ^ (Davis, Brian 2010).
  5. ^ a b Funk, Emily; Breen, Catriona; Sanketi, Bhargav; Kurpios, Natasza; McCune, Amy (2020). "Changing in Nkx2.1, Sox2, Bmp4, and Bmp16 expression underlying the lung-to-gas bladder evolutionary transition in ray-finned fishes". Evolution & Development. 22 (5): 384–402. doi:10.1111/ede.12354. PMC 8013215. PMID 33463017.
  6. ^ "Actinopterygii Klein, 1885". www.gbif.org. Retrieved 20 September 2021.
  7. ^ Dorit, R.L.; Walker, W.F.; Barnes, R.D. (1991). Zoology. Saunders College Publishing. p. 819. ISBN 978-0-03-030504-7.
  8. ^ Avise, J.C.; Mank, J.E. (2009). "Evolutionary perspectives on hermaphroditism in fishes". Sexual Development. 3 (2–3): 152–163. doi:10.1159/000223079. PMID 19684459. S2CID 22712745.
  9. ^ Pitcher, T (1993). The Behavior of Teleost Fishes. London: Chapman & Hall.
  10. ^ a b c Reynolds, John; Nicholas B. Goodwin; Robert P. Freckleton (19 March 2002). "Evolutionary Transitions in Parental Care and Live Bearing in Vertebrates". Philosophical Transactions of the Royal Society B: Biological Sciences. 357 (1419): 269–281. doi:10.1098/rstb.2001.0930. PMC 1692951. PMID 11958696.
  11. ^ Maxwell; et al. (2018). "Re‐evaluation of the ontogeny and reproductive biology of the Triassic fish Saurichthys (Actinopterygii, Saurichthyidae)". Palaeontology. 61: 559–574. doi:10.5061/dryad.vc8h5.
  12. ^ Clutton-Brock, T. H. (1991). The Evolution of Parental Care. Princeton, NJ: Princeton UP.
  13. ^ Werren, John; Mart R. Gross; Richard Shine (1980). "Paternity and the evolution of male parentage". Journal of Theoretical Biology. 82 (4): 619–631. doi:10.1016/0022-5193(80)90182-4. PMID 7382520. Retrieved 15 September 2013.
  14. ^ Baylis, Jeffrey (1981). "The Evolution of Parental Care in Fishes, with reference to Darwin's rule of male sexual selection". Environmental Biology of Fishes. 6 (2): 223–251. doi:10.1007/BF00002788. S2CID 19242013.
  15. ^ Wootton, Robert J.; Smith, Carl (2014). Reproductive Biology of Teleost Fishes. Wiley. ISBN 978-1-118-89139-1.
  16. ^ Sallan, Lauren C. (February 2014). "Major issues in the origins of ray-finned fish (Actinopterygii) biodiversity". Biological Reviews. 89 (4): 950–971. doi:10.1111/brv.12086. hdl:2027.42/109271. PMID 24612207. S2CID 24876484.
  17. ^ a b c d Thomas J. Near; et al. (2012). "Resolution of ray-finned fish phylogeny and timing of diversification". PNAS. 109 (34): 13698–13703. Bibcode:2012PNAS..10913698N. doi:10.1073/pnas.1206625109. PMC 3427055. PMID 22869754.
  18. ^ a b Betancur-R, Ricardo; et al. (2013). "The Tree of Life and a New Classification of Bony Fishes". PLOS Currents Tree of Life. 5 (Edition 1). doi:10.1371/currents.tol.53ba26640df0ccaee75bb165c8c26288. PMC 3644299. PMID 23653398. Archived from the original on 13 October 2013.
  19. ^ Laurin, M.; Reisz, R.R. (1995). "A reevaluation of early amniote phylogeny". Zoological Journal of the Linnean Society. 113 (2): 165–223. doi:10.1111/j.1096-3642.1995.tb00932.x.
  20. ^ "Fossilworks: Andreolepis". Archived from the original on 12 February 2010. Retrieved 14 May 2008.
  21. ^ Arratia, G. (2015). "Complexities of early teleostei and the evolution of particular morphological structures through time". Copeia. 103 (4): 999–1025. doi:10.1643/CG-14-184. S2CID 85808890.
  22. ^ Romano, Carlo; Koot, Martha B.; Kogan, Ilja; Brayard, Arnaud; Minikh, Alla V.; Brinkmann, Winand; Bucher, Hugo; Kriwet, Jürgen (February 2016). "Permian-Triassic Osteichthyes (bony fishes): diversity dynamics and body size evolution". Biological Reviews. 91 (1): 106–147. doi:10.1111/brv.12161. PMID 25431138. S2CID 5332637.
  23. ^ a b "Chondrosteans: Sturgeon Relatives". paleos.com. Archived from the original on 25 December 2010.
  24. ^ Theodore Holmes Bullock; Carl D. Hopkins; Arthur N. Popper (2005). Electroreception. Springer Science+Business Media, Incorporated. p. 229. ISBN 978-0-387-28275-6.
  25. ^ Betancur-Rodriguez; et al. (2017). "Phylogenetic Classification of Bony Fishes Version 4". BMC Evolutionary Biology. 17 (1): 162. doi:10.1186/s12862-017-0958-3. PMC 5501477. PMID 28683774.
  26. ^ "Actinopterygii". Integrated Taxonomic Information System. Retrieved 3 April 2006.
  27. ^ R. Froese and D. Pauly, ed. (February 2006). "FishBase". Archived from the original on 5 July 2018. Retrieved 8 January 2020.
  28. ^ Van der Laan, Richard (2016). Family-group names of fossil fishes. doi:10.13140/RG.2.1.2130.1361.
  29. ^ Xu, Guang-Hui (9 January 2021). "A new stem-neopterygian fish from the Middle Triassic (Anisian) of Yunnan, China, with a reassessment of the relationships of early neopterygian clades". Zoological Journal of the Linnean Society. 191 (2): 375–394. doi:10.1093/zoolinnean/zlaa053. ISSN 0024-4082.
  30. ^ In Nelson, Polypteriformes is placed in its own subclass Cladistia.
  31. ^ In Nelson and ITIS, Syngnathiformes is placed as the suborder Syngnathoidei of the order Gasterosteiformes.

External links[edit]