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Description of Elasmobranchii

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The elasmobranchs, the skates and rays, together with the chimaeras make up the cartilaginous fish (they have no calcified bones). Also, unlike the bony fish, elasmobrachs have no swim bladders. Again, unlike bony fish with one gill cleft, these fish have five to seven pairs of gill clefts opening individually to the exterior, rigid dorsal fins, and small placoid scales. The teeth lie in several series. The upper jaw is not fused to the cranium, and the lower jaw is articulated with the upper. The eyes have a tapetum lucidum. The inner margin of each pelvic fin in the male fish is grooved to constitute a clasper for the transmission of sperm. These fish are widely distributed in tropical and temperate marine waters, a few occur in freshwaters. There are about 1000 species.
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Comprehensive Description

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From the enormous whale sharks(1) and manta rays(2) to the tiny dwarf lanternsharks(3) and short-nosed electric rays,(2) the elasmobranchs (the sharks, skates, and rays(4)) are a diverse group of fishes with some 900-1150 species(4,5) living all over the world (6,7) in both marine and freshwater habitats.(2,8) The elasmobranchs and one other group, the chimaeras, make up the class of cartilaginous fish or chondrichthyans;(4) as these fish have skeletons made up of a strong, flexible, and light material called cartilage,(9) rather than bone, they are fundamentally different from other fish.(2,4,7) Living elasmobranchs also share, among other physical features, rows of replaceable teeth(5) and 5-7 gill slits on each side of their body.(2) Although these creatures are ancient—the first elasmobranchs evolved at least 400 million years ago(1,4,6,7)—they have many sophisticated senses,(8,10) including the ability to perceive very small shifts in electricity around them.(10,11) Sharks, as well as rays and skates (distinguishable from sharks by, among other characteristics, their generally flattened, diamond-shaped bodies(2)), frequently use this sense for finding prey, as well as for navigation;(10,11) in at least some elasmobranchs this sense may even be connected with various social and mating behaviors.(11) As the skillful hunters that many of them are, elasmobranchs are crucial parts of their environments, often serving as the top predators in the food chain and keeping the ecosystem in balance.(6,12,13) These animals also have an important relationship with humans. Some rays, such as stingrays and electric rays, can cause injury to people.(2,8) Much more present in the public imagination are shark attacks, which, while in fact rare, have given sharks a very dark reputation.(8,12,14) But although elasmobranchs can pose dangers to humans, humans pose a much greater danger to them.(13) For over 5000 years shark meat has been used as a food source and in some countries today it is considered a delicacy;(7) ray and skate meat are also sometimes consumed (2) and shark skin is an expensive product in some markets.(7) Because elasmobranchs generally grow slowly, reproduce late in life, and produce only a small number of offspring, they are particularly sensitive to human exploitation,(1,4,7,12,13,15) and as a result of overfishing and accidental catching (“bycatch”)(4,6,13,15,16)—as well as increasing human presence on and damage to the coastal environment(13,15)—many elasmobranchs worldwide are in decline.(13)
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Behavior

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As an apex predator, sharks play a pivotal role in controlling the populations of various species of fish and other aquatic life forms. Sharks are not much of a threat towards humans, often mistaking limbs for helpless prey. Species such as the Tiger and Bull will attempt to eat anything, more so due to the sake of their sizes. Sharks are carnivorous, but they very rarely change up their diet; most species will eat plankton and smaller types of fish. Sharks are very migratory, often spanning vast amounts of ocean to meet at breeding grounds. They will swim in schools, and are very social amongst one another. Their level of intelligence is quite high, and, for example, show signs of curiosity when playing and will move erratically when they feel threatened.
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Introduction

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Sharks, skates, and rays, which together form a group of about 900-1150 species(1,2) of ocean-dwelling and freshwater-dwelling fish(3,4) called elasmobranchs,(1) are some of the most fascinating creatures of the deep. While they come in many sizes and shapes—from the giant whale shark(5) and the huge manta ray (3) to the dwarf lanternshark(6) and the tiny short-nosed electric ray,(3) and the from the odd-looking hammerhead sharks(4) to the totally bizarre sawfish(3)—all living elasmobranchs share certain key features. First of all, their skeletons are made up of a strong, flexible, and light material called cartilage,(7) rather than bone, making them (along with another fish group called chimaeras(1)) fundamentally different from other fish.(1,3,8) Other important characteristics include their rows of replaceable teeth(2) and the 5-7 gill slits on each side of their body.(3) In addition, although these creatures are ancient—the first elasmobranchs evolved at least 400 million years ago!(1,5,8,9)—they have many highly-developed senses,(4,10) including the amazing ability to perceive tiny changes in electricity around them.(10,11) Sharks, as well as rays and skates (which you can tell apart from sharks by their generally flattened, diamond-shaped bodies(3)), often use this sense for finding prey, as well as for finding their way through the water.(10,11) In at least some elasmobranchs this sense may even be used in various social and mating behaviors.(11) In part thanks to this electric sense, many elasmobranchs are skillful hunters, often serving as the top predators in the food chain and keeping their environments in the proper balance.(9,12,13) These creatures also have an important relationship with humans. Some rays, such as stingrays and electric rays, can cause injury to people.(3,4) And even if you haven’t heard much about the dangers of those fish, you’ve definitely heard of shark attacks, which have given sharks a very dark reputation even though these attacks are actually rare.(4,12,14) In fact, although elasmobranchs can pose dangers to humans, humans pose a much greater danger to them.(13) For over 5000 years shark meat has been eaten by people,(8) and ray meat, skate meat, shark skin, and other elasmobranch products are also sometimes used by humans today.(3,8,13) Overfishing, accidental catching (called “bycatch”),(1,9,13,15,16) higher numbers of people living on the coast, and greater damage to coastal environments(13,15) are all threatening sharks, skates, and rays. And because elasmobranchs generally grow slowly, reproduce late in life, and have only a small number of children, they have trouble recovering from population decline caused by humans.(1,5,8,12,13,15) As a result, many elasmobranchs around the world are endangered.(13,15)

References

  • 13. Simpfendorfer, C. A., M. R. Heupel, W. T. White, and N. K. Dulvy. “The Importance of Research and Public Opinion to Conservation Management of Sharks and Rays: A Synthesis.” Marine and Freshwater Research 62.6 (2011): 518-527.
  • 14. “Shark Attacks in Perspective.” Florida Museum of Natural History Ichthyology Department: Sharks. International Shark Attack File. 1991. 21 Jul. 2011. http://www.flmnh.ufl.edu/fish/sharks/Attacks/perspect.htm
  • 4. Kyne, Peter M. and Colin A. Simpfendorfer. “A Collation and Summarization of Available Data on Deepwater Chondrichthyans: Biodiversity, Life History and Fisheries.” IUCN SSC Shark Specialist Group. 2007.
  • References:
  • 1. Hoenig, John M. and Samuel H. Gruber. “Life-History Patterns in the Elasmobranchs: Implications for Fisheries Management.” NOAA Technical Report NMFS 90: Elasmobranchs as Living Resources: Advances in the Biology, Ecology, Systematics, and the Status of the Fisheries. Harold L. Pratt, Jr., Samuel H. Gruber, and Toru Taniuchi, eds. Springfield: U.S. Department of Commerce, 1990.
  • 2. Bester, Cathleen. “Ray and Skate Basics.” Florida Museum of Natural History Ichthyology Department: Education. 7 Sept. 2011. http://www.flmnh.ufl.edu/fish/education/questions/raybasics.html
  • 3. Martin, R. Aidan. “Order Squaliformes: Dogfish Sharks – 119 Species.” ReefQuest Centre for Shark Research. 21 Jul. 2011. http://www.elasmo-research.org/education/shark_profiles/squaliformes.htm
  • 5. Compagno, Leonard J. V. “Systematics and Body Form.” Sharks, Skates, and Rays: The Biology of Elasmobranch Fishes. Ed. William C. Hamlett. Baltimore: Johns Hopkins University Press, 1999.
  • 6. “Sharks: Overview.” Oceana. 2010. 25 Jul. 2011. http://na.oceana.org/en/our-work/protect-marine-wildlife/sharks/overview
  • 7. Schubring, Reinhard. “DSC Measurements on Sharks.” Thermochimica Acta 458.1-2 (2007): 124-131.
  • 8. “Know Before You Go – Marine Animals.” Wet Tropics Visitor Information. Wet Tropics Management Authority. 2010. 7 Sept. 2011. http://www.wettropics.gov.au/vi/vi_marine.html
  • 9. Martin, R. Aidan. “The Importance of Being Cartilaginous.” ReefQuest Centre for Shark Research. 21 Jul. 2011.
  • http://www.elasmo-research.org/education/topics/p_cartilage.htm
  • 10. Bleckmann, Horst and Michael H. Hofmann. “Special Senses.” Sharks, Skates, and Rays: The Biology of Elasmobranch Fishes. Ed. William C. Hamlett. Baltimore: Johns Hopkins University Press, 1999.
  • 11. Tricas, T. C. and J. G. New. “Sensitivity and Response Dynamics of Elasmobranch Electrosensory Primary Afferent Neurons to Near Threshold Fields.” Journal of Comparative Physiology A—Sensory Neural and Behavioral Physiology 182.1 (1998): 89-101.
  • 12. Branstetter, Steven, ed. NOAA Technical Report NMFS 115: Conservation Biology of Elasmobranchs. Springfield: U.S. Department of Commerce, 1993.
  • 15. Cavanagh, Rachel D. and Claudine Gibson. Overview of the Conservation Status of Cartilaginous Fishes (Chondrichthyans) in the Mediterranean. Malaga: IUCN, 2007.
  • 16. Ebert, David A. and James A. Sulikowski. “Preface: Biology of Skates.” Environmental Biology of Fishes 80.2-3 (2007): 107-110.

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Elasmobranchii

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Cetorhinus maximus by greg skomal.JPG
Elasmobranchs lack swim bladders, and maintain buoyancy with oil that they store in their livers. Some deep sea sharks are targeted by fisheries for this liver oil, including the school, gulper and basking sharks (pictured).[2] All three of these species have been assessed by the IUCN as vulnerable due to overfishing.[3][4][5]
 src=
Radiation of elasmobranchs, based on Michael Benton, 2005.[6]
From a practical point of view the life-history pattern of elasmobranchs makes this group of animals extremely susceptible to over fishing. It is no coincidence that the commercially exploited marine turtles and baleen whales, which have life-history patterns similar to the sharks, are also in trouble.[7]

Elasmobranchii (/ɪˌlæzməˈbræŋki/[8]) is a subclass of Chondrichthyes or cartilaginous fish, including the sharks (superorder Selachii) and the rays, skates, and sawfish (superorder Batoidea). Members of this subclass are characterised by having four (tawny nurse sharks have 4 pairs of gills) to seven pairs of gill clefts opening individually to the exterior, rigid dorsal fins and small placoid scales on the skin. The teeth are in several series; the upper jaw is not fused to the cranium, and the lower jaw is articulated with the upper. The details of this jaw anatomy vary between species, and help distinguish the different elasmobranch clades. The pelvic fins in males are modified to create claspers for the transfer of sperm. There is no swim bladder; instead, these fish maintain buoyancy with large livers rich in oil.

The earliest elasmobranch fossils came from the Devonian and many surviving orders date back to the Cretaceous, or even earlier. Many species became extinct during the Permian and there was a burst of adaptive radiation during the Jurassic.

Description

Elasmobranchii is one of the two subclasses of cartilaginous fish in the class Chondrichthyes, the other being Holocephali (chimaeras).

Members of the elasmobranchii subclass have no swim bladders, five to seven pairs of gill clefts opening individually to the exterior, rigid dorsal fins, and small placoid scales. The teeth are in several series; the upper jaw is not fused to the cranium, and the lower jaw is articulated with the upper.

Extant elasmobranchs exhibit several archetypal jaw suspensions: amphistyly, orbitostyly, hyostyly, and euhyostyly. In amphistyly, the palatoquadrate has a postorbital articulation with the chondrocranium from which ligaments primarily suspend it anteriorly. The hyoid articulates with the mandibular arch posteriorly, but it appears to provide little support to the upper and lower jaws. In orbitostyly, the orbital process hinges with the orbital wall and the hyoid provides the majority of suspensory support.

In contrast, hyostyly involves an ethmoid articulation between the upper jaw and the cranium, while the hyoid most likely provides vastly more jaw support compared to the anterior ligaments. Finally, in euhyostyly, also known as true hyostyly, the mandibular cartilages lack a ligamentous connection to the cranium. Instead, the hyomandibular cartilages provide the only means of jaw support, while the ceratohyal and basihyal elements articulate with the lower jaw, but are disconnected from the rest of the hyoid.[9][10][11] The eyes have a tapetum lucidum. The inner margin of each pelvic fin in the male fish is grooved to constitute a clasper for the transmission of sperm. These fish are widely distributed in tropical and temperate waters.[12]

Many fish maintain buoyancy with swim bladders. However elasmobranchs lack swim bladders, and maintain buoyancy instead with large livers that are full of oil.[13] This stored oil may also function as a nutrient when food is scarce.[7][14] Deep sea sharks are usually targeted for their oil, because the livers of these species can weigh up to 20% of their total weight.[2]

Evolution

Fossilised shark teeth are known from the early Devonian, around 400 million years ago. During the following Carboniferous period, the sharks underwent a period of diversification, with many new forms evolving. Many of these became extinct during the Permian, but the remaining sharks underwent a second burst of adaptive radiation during the Jurassic, around which time the skates and rays first appeared. Many surviving orders of elasmobranch date back to the Cretaceous, or earlier.[15]

Habitats

Elasmobranchs are mostly a marine taxon, but we know several species that live in freshwater environment (approximately 60 species which represent only 5% of the 1154 described species). They can be divided into two groups.

The euryhaline elasmobranchs, which are marine species that may survive and reproduce in freshwater environment, and the obligated freshwater elasmobranchs. The second group contains elasmobranchs that only lives in freshwater environment their entire life. This group contains only one clade: the subfamily Potamotrygoninae. This clade is endemic to one specific region (which means that they can only be seen in those regions): tropical, subtropical water and wetland of South America.

Recent researches in Paraná river[16] have shown that obligated freshwater elasmobranchs were more susceptible to anthropogenic threats as overfishing and destruction of habitats due to the very small place they live in compared to the marine species.

New research has highlighted the importance of coastal wetlands, like mangroves and seagrasses, as habitats for many species of elasmobranch[17]

Taxonomy

Compagno's 2005 Sharks of the World arranges the class as follows:

Recent molecular studies suggest the Batoidea are not derived selachians as previously thought. Instead, skates and rays are a monophyletic superorder within Elasmobranchii that shares a common ancestor with the selachians.[18][19]

See also

References

  1. ^ Märss, Tiiu; Gagnier, Pierre-Yves (2001). "A new chondrichthyan from the Wenlock, Lower Silurian, of Baillie-Hamilton Island, the Canadian Arctic". Journal of Vertebrate Paleontology. 21 (4): 693–701. doi:10.1671/0272-4634(2001)021[0693:ANCFTW]2.0.CO;2.
  2. ^ a b Vannuccini, Stefania (2002) Shark liver oil products Archived 2013-06-26 at the Wayback Machine In: Shark Utilization, Marketing and Trade, Fisheries Technical paper 389, FAO, Rome. ISBN 92-5-104361-2.
  3. ^ Fowler, S.L. (2005). "Cetorhinus maximus". IUCN Red List of Threatened Species. IUCN. 2005: e.T4292A10763893. doi:10.2305/IUCN.UK.2005.RLTS.T4292A10763893.en.
  4. ^ "Galeorhinus galeus (School shark)". IUCN Red List of Threatened Species. IUCN. 2005-06-17. 2005-06-17. Retrieved 2013-03-26.old-form url
  5. ^ Guallart; et al. (2006). "Centrophorus granulosus". IUCN Red List of Threatened Species. IUCN. 2006. Retrieved 11 May 2006.old-form url
  6. ^ Benton, Michael J. (2015). Vertebrate Palaeontology (3rd ed.). Blackwell. p. 185. ISBN 9781118406847. OCLC 945675149.
  7. ^ a b Hoenig, J.M. and Gruber, S.H. (1990) "Life-history patterns in the elasmobranchs: implications for fisheries management" Archived 2013-02-18 at the Wayback Machine In: Elasmobranchs as living resources: advances in the biology, ecology, systematics and the status of the fisheries, eds. J. H. L. Pratt, S. H. Gruber and T. Taniuchi, US Department of Commerce, NOAA technical report NMFS 90, pp.1–16.
  8. ^ "Elasmobranchii". Merriam-Webster Dictionary.
  9. ^ Wilga, C.D. (2005). "Morphology and evolution of the jaw suspension in lamniform sharks". Journal of Morphology. 265 (1): 102–19. doi:10.1002/jmor.10342. PMID 15880740.
  10. ^ Wilga, C. D.; Motta, P. J.; Sanford, C. P. (2007). "Evolution and ecology of feeding in elasmobranchs". Integrative and Comparative Biology. 47 (1): 55–69. doi:10.1093/icb/icm029. PMID 21672820.
  11. ^ Wilga, Cheryl A.D. (2008). "Evolutionary divergence in the feeding mechanism of fishes". Acta Geologica Polonica. 58 (2): 113–20. Archived from the original on 2018-08-19. Retrieved 2017-05-24.
  12. ^ Bigelow, Henry B.; Schroeder, William C. (1948). Fishes of the Western North Atlantic. Sears Foundation for Marine Research, Yale University. pp. 64–65. ASIN B000J0D9X6.
  13. ^ Oguri, M (1990) "A review of selected physiological characteristics unique to elasmobranchs" Archived 2013-02-18 at the Wayback Machine In: Elasmobranchs as living resources: advances in the biology, ecology, systematics and the status of the fisheries, eds. J. H. L. Pratt, S. H. Gruber and T. Taniuchi, US Department of Commerce, NOAA technical report NMFS 90, pp.49–54.
  14. ^ Bone, Q.; Roberts, B. L. (2009). "The density of elasmobranchs". Journal of the Marine Biological Association of the United Kingdom. 49 (4): 913. doi:10.1017/S0025315400038017.
  15. ^ Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 26. ISBN 978-1-84028-152-1.
  16. ^ Lucifora, Luis O.; Balboni, Leandro; Scarabotti, Pablo A.; Alonso, Francisco A.; Sabadin, David E.; Solari, Agustín; Vargas, Facundo; Barbini, Santiago A.; Mabragaña, Ezequiel; Díaz De Astarloa, Juan M. (2017). "Decline or stability of obligate freshwater elasmobranchs following high fishing pressure" (PDF). Biological Conservation. 210: 293–298. doi:10.1016/j.biocon.2017.04.028.
  17. ^ Sievers, Michael; Brown, Christopher J.; Tulloch, Vivitskaia J.D.; Pearson, Ryan M.; Haig, Jodie A.; Turschwell, Mischa P.; Connolly, Rod M. (May 2019). "The Role of Vegetated Coastal Wetlands for Marine Megafauna Conservation". Trends in Ecology & Evolution. 34: 807–817. doi:10.1016/j.tree.2019.04.004. PMID 31126633.
  18. ^ Winchell, Christopher J; Martin, Andrew P; Mallatt, Jon (2004). "Phylogeny of elasmobranchs based on LSU and SSU ribosomal RNA genes". Molecular Phylogenetics and Evolution. 31 (1): 214–24. doi:10.1016/j.ympev.2003.07.010. PMID 15019621.
  19. ^ Douady, Christophe J.; Dosay, Miné; Shivji, Mahmood S.; Stanhope, Michael J. (2003). "Molecular phylogenetic evidence refuting the hypothesis of Batoidea (rays and skates) as derived sharks". Molecular Phylogenetics and Evolution. 26 (2): 215–21. doi:10.1016/S1055-7903(02)00333-0. PMID 12565032.

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Elasmobranchii: Brief Summary

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Cetorhinus maximus by greg skomal.JPG Elasmobranchs lack swim bladders, and maintain buoyancy with oil that they store in their livers. Some deep sea sharks are targeted by fisheries for this liver oil, including the school, gulper and basking sharks (pictured). All three of these species have been assessed by the IUCN as vulnerable due to overfishing.  src= Radiation of elasmobranchs, based on Michael Benton, 2005. From a practical point of view the life-history pattern of elasmobranchs makes this group of animals extremely susceptible to over fishing. It is no coincidence that the commercially exploited marine turtles and baleen whales, which have life-history patterns similar to the sharks, are also in trouble.

Elasmobranchii (/ɪˌlæzməˈbræŋkiaɪ/) is a subclass of Chondrichthyes or cartilaginous fish, including the sharks (superorder Selachii) and the rays, skates, and sawfish (superorder Batoidea). Members of this subclass are characterised by having four (tawny nurse sharks have 4 pairs of gills) to seven pairs of gill clefts opening individually to the exterior, rigid dorsal fins and small placoid scales on the skin. The teeth are in several series; the upper jaw is not fused to the cranium, and the lower jaw is articulated with the upper. The details of this jaw anatomy vary between species, and help distinguish the different elasmobranch clades. The pelvic fins in males are modified to create claspers for the transfer of sperm. There is no swim bladder; instead, these fish maintain buoyancy with large livers rich in oil.

The earliest elasmobranch fossils came from the Devonian and many surviving orders date back to the Cretaceous, or even earlier. Many species became extinct during the Permian and there was a burst of adaptive radiation during the Jurassic.

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