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Squaliformes

Squaliformes
Temporal range:
Pacific spiny dogfish, Squalus suckleyi
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Clade: Neoselachii
Subdivision: Selachimorpha
Superorder: Squalomorphii
Order: Squaliformes
Goodrich, 1909
Type species
Squalus acanthias

The Squaliformes /ˌskwɒlɪˈfɔːrmiːz/ are an order of sharks that includes about 126 species in seven families.

Members of the order have two dorsal fins, which usually possess spines, they usually have a sharp head, no anal fin or nictitating membrane, and five to seven gill slits. In most other respects, however, they are quite variable in form and size. Most species of the squaliform order live in saltwater or brackish water. They are found worldwide, from northern to tropical waters, and from shallow coastal seas to the open ocean.[2]

All members of the family Etmoperidae and Dalatiidae and Zameus squamulosus possess photophores, luminous organs, and exhibit intrinsic bioluminescence.[3] Bioluminescence evolved once in Squaliformes, approximately 111–153 million years ago, and helped the Squaliformes radiate and adapt to the deep sea.[3][4] The common ancestor of Dalatiidae, Etmopteridae, Somniosidae, and Oxynotidae possessed a luminous organ and used bioluminescence for camouflage by counterillumination.[3][5] Counterillumination is an active form of camouflage in which an organism emits light to match the intensity of downwelling light to hide from predators below.[6] Currently, bioluminescence provides different functions for Squaliformes based on the family. Dalatiidae and Zameus squamulosus possess simple photophores and use bioluminescence for ventral counter-illumination.[5] Etmopteridae possess more complex photophores [7] and utilize bioluminescence for ventral counter illumination as well as species recognition.[8]

  1. ^ Froese, Rainer, and Daniel Pauly, eds. (2009). "Squaliformes" in FishBase. January 2009 version.
  2. ^ Stevens, J. & Last, P.R. (1998). Paxton, J.R. & Eschmeyer, W.N. (eds.). Encyclopedia of Fishes. San Diego: Academic Press. p. 64. ISBN 978-0-12-547665-2.
  3. ^ a b c Flammesbeck, C. K.; Pollerspöck, J.; Schedel, F. D. B.; Matzke, N. J.; Straube, N. (2018). "Of teeth and trees: a fossil tip dating approach to infer divergence times of extinct and extant squaliform sharks". 2dh Annual Conference of the European Elasmobranch Association: 57.
  4. ^ Davis, M. P.; Sparks, J. S.; Smith, W. L. (2016). "Repeated and widespread evolution of bioluminescence in marine fishes". PLOS ONE. 11 (6): e0155154. doi:10.1371/journal.pone.0155154. PMC 4898709. PMID 27276229.
  5. ^ a b Straube, N.; Li, C.; Claes, J. M.; Corrigan, S.; Naylor, J. P. (2015). "Molecular phylogeny of squaliformes and first occurrence of bioluminescence in sharks". BMC Evolutionary Biology. 15: 62. PMC 4537554. PMID 26277575.
  6. ^ Hastings, J. W. (1971). "Light to hide by: ventral luminescence to camouflage the silhouette". Science. 173 (4001): 1016–1017. doi:10.1126/science.173.4001.1016. PMID 17796582. S2CID 5680392.
  7. ^ Claes, J. M.; Mallefet, J. (2009). "Bioluminescence of sharks: first synthesis". Kerala: Research Signpost: 51–65.
  8. ^ Claes, J. M.; Nilsson, D. E.; Mallefet, J.; Straube, N. (2015). "The presence of lateral photophores correlates with increased speciation in deep-sea bioluminescent sharks". Royal Society Open Science. 2 (7): 150219. doi:10.1098/rsos.150219. PMC 4632593. PMID 26587280.

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