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The angelsharks are a group of
shark Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachi ...
s in the
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
''Squatina'' of the
family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
Squatinidae. They commonly inhabit sandy seabeds close to in depth. Many species are now classified as critically endangered by the
International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...
. Once common over large areas of the Northeast Atlantic from Norway, Sweden, Morocco, and the Canary Islands, to the Mediterranean and Black Seas, there is now significant fishing pressure which has resulted in significant population decline. Squatinidae are unusual in having flattened bodies and broad
pectoral fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...
s that give them a strong resemblance to rays. This genus is the only one in its family and order Squatiniformes. They occur worldwide in temperate and tropical seas. Most
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...
inhabit shallow temperate or tropical seas, but a few species inhabit deeper water, down to . Angel sharks are sometimes called monkfish, although this name is also applied to members of the genus '' Lophius''. While some species occur over a wide geographic range, the majority are restricted to a smaller area. Restriction in geographic range might be as a result of the behavior of ''Squatina'' species, which are
ambush predator Ambush predators or sit-and-wait predators are carnivorous animals that capture or trap prey via stealth, luring or by (typically instinctive) strategies utilizing an element of surprise. Unlike pursuit predators, who chase to capture prey ...
s with a corresponding stationary bottom-dwelling habit. Thus, trans-ocean migration is extremely unlikely, even though large-scale coastal migratory patterns have been reported in species such as '' Squatina squatina''.


Appearance and biology

The angel shark has unique features that differentiates them from other sharks. They are considered as smaller sized sharks because they grow up to only and can weigh around , as opposed to the whale shark that can measure up to and weigh . While the anterior part of the angel shark's body is broad and flattened, the posterior part retains a muscular appearance more typical of other sharks. The eyes and spiracles are dorsal and the five
gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they ar ...
slits are on its back. Both the pectoral and
pelvic fin Pelvic fins or ventral fins are paired fins located on the ventral surface of fish. The paired pelvic fins are homologous to the hindlimbs of tetrapods. Structure and function Structure In actinopterygians, the pelvic fin consists of two ...
s are large and held horizontally. There are two
dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through c ...
s, no
anal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as see ...
and unusually for sharks, the lower lobe of the
caudal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...
is longer than the upper lobe. Most types grow to a length of 1.5 m (5 ft), with the Japanese angel shark, known to reach 2 m. Some angel sharks have deformities that have been described in elasmobranchs. These can include skeletal deformities, as lateral spinal curvature (scoliosis), humpback curvature (khyphosis), axial spinal curvature (lordosis), missing fins, additional fins, deformed snout, and more. These abnormalities have only been found in a few sharks, but the causes of these deformities have been found to be from dietary nutritional imbalance, genetic factors, parasites, traumatic injuries, or stress in the specimen. In 2015, two sharks were captured and examined, and both showed a lateral spinal curvature (scoliosis) and also a humpback curvature. Both the animals had the curvature in the middle of their pectoral fins, but the deformity did not affect their swimming capacity. Spinal scoliosis has been reported to be diverse in sharks, but mostly in pelagic sharks that depend on their swimming abilities to catch their prey. For the angel shark, specifically ''S. squatina'', these curvatures do not seem to significantly affect its hunting capacity, which involves burying itself to ambush their prey. Right now, research is assuming most physical injuries are caused by human interactions because of the constant interference in coastal areas, where most of the sharks reside. There have been few attacks reported, and what few have occurred were due to accidental stepping on of buried newborn sharks. Landings of Pacific angel shark increased through the mid-1980s and reached over 1125 tonnes in 1986, becoming the shark species with the highest total reported landings off the US West coast that year. Angel sharks possess extensible jaws that can rapidly snap upwards to capture prey and have long, needle-like teeth. They bury themselves in loose sediment lying in wait for prey, which includes
fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...
,
crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapoda, decapods, ostracoda, seed shrimp, branchiopoda, branchiopods, argulidae, fish lice, krill, remipedes, isopoda, isopods, barnacles, copepods, ...
s and various types of
mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000  extant species of molluscs are recognized. The number of fossil species is e ...
s. They are ovoviviparous, producing litters of up to 13 pups. Pacific angel shark pups are born from March to June in deep water — generally 180 to 300 feet (55 and 90 metres) — possibly to protect the pups from predators. Angel sharks usually reside in depths of and can be seen on muddy or soft benthic substrata where they can easily blend in as they lie in wait. Members of the family Squatinidae have a unique camouflage method, which goes hand in hand with how they obtain their food, involving lying still on the sea floor, making rapid lunges at passing prey, and using negative pressure to capture prey by sucking it into their mouths.


Species analysis

Morphological identification in the field can be difficult due to discontinuity and similarity of species. In this specific circumstance, the sharks' place within the genus ''Squatina'' comprises three species in the southern part of the western Atlantic. The three species observed were ''Squatina guggenheim'', ''S. occulta'' and the Brazilian guitarfish ''Pseudobatos horkelii''. These three species are listed in the IUCN Red List as threatened, and they are now protected under Brazilian law, which makes angling and exchange illegal. To prevent landing and trade of these endangered species along the São Paulo, DNA barcoding was used. DNA barcoding revealed fishing and trafficking of these protected species.


Habitat

Angel sharks inhabit temperate and tropical marine environments. They are generally found in shallow waters at depths from 10 to 328 feet off coasts. They are known to bury themselves in sandy or muddy environments during the day, where they remain camouflaged for weeks until a desirable prey crosses paths with them. At night, they take a more active approach and cruise on the bottom of the floor. ''Squatina'' preys on fish, crustaceans, and cephalopods.


Behavior

Although this shark is a bottom-dweller and appears harmless, it can inflict painful lacerations if provoked, due to its powerful jaws and sharp teeth. It may bite if a diver approaches the head or grabs the tail.Bester, C. (2010)
Florida Museum of Natural History. Pacific Angelshark.
/ref> Angelsharks have a unique way of breathing compared to most other benthic fish. They do not pump out water from the oropharyngeal cavity like other fish. Instead they use gill flaps located under their body to pump out water during respiration. Doing so also allows them to be more discreet and prevent detection.


Commercial value

Prior to the late 1980s, the Pacific angel shark was considered a "munk fish". It was a byproduct of commercial
gillnetting Gillnetting is a fishing method that uses gillnets: vertical panels of netting that hang from a line with regularly spaced floaters that hold the line on the surface of the water. The floats are sometimes called "corks" and the line with corks is ...
, with no commercial appeal and was used only for crab bait. In 1977, Michael Wagner, a fish processor in
Santa Barbara, California Santa Barbara ( es, Santa Bárbara, meaning " Saint Barbara") is a coastal city in Santa Barbara County, California, of which it is also the county seat. Situated on a south-facing section of coastline, the longest such section on the West ...
, in cooperation with local commercial fishermen, developed the market for angel sharks. The annual take of angel shark in 1977 was an estimated 147 kg. By 1985, the annual take of angel shark on the central California coast had increased to more than 454 metric tons or an estimated 90,000 sharks. The population declined dramatically and is now regulated. Angel sharks live very close to shore, resulting in high bycatch rates. In 1991, the use of gillnets in nearshore state waters of California was forbidden, and fishing was restricted in a larger portion of the Pacific angel shark's range. In April 2008, the UK government afforded the angel shark full protection under the Wildlife and Countryside Act. Once considered abundant in the Atlantic Ocean, the angel shark (''Squatina squatina'') was classified as "critically endangered" in 2010.


Species

Currently, the 26 recognized species in this genus are: * ''
Squatina aculeata The sawback angelshark (''Squatina aculeata'') is an angelshark of the family (biology), family Squatinidae It is one of rarest species of sharks known to date, and one of the three species of angelsharks that inhabits the Mediterranean. The Sawb ...
'' G. Cuvier, 1829 (sawback angelshark) * '' Squatina africana''
Regan The family name Regan, along with its cognates O'Regan, O Regan, Reagan, and O'Reagan, is an Anglicized form of the Irish surname Ó Riagáin or Ó Ríogáin, from Ua Riagáin. The meaning is likely to have originated in ancient Gaelic ''ri'' ...
, 1908
(African angelshark) * '' Squatina albipunctata''
Last A last is a mechanical form shaped like a human foot. It is used by shoemakers and cordwainers in the manufacture and repair of shoes. Lasts typically come in pairs and have been made from various materials, including hardwoods, cast iron ...
& W. T. White, 2008
(eastern angelshark) * ''
Squatina argentina The Argentine angelshark (''Squatina argentina'') is an angelshark The angelsharks are a group of sharks in the genus ''Squatina'' of the family Squatinidae. They commonly inhabit sandy seabeds close to in depth. Many species are now classif ...
'' ( Marini, 1930) (Argentine angelshark) * '' Squatina armata'' ( Philippi , 1887) (Chilean angelshark) * '' Squatina australis''
Regan The family name Regan, along with its cognates O'Regan, O Regan, Reagan, and O'Reagan, is an Anglicized form of the Irish surname Ó Riagáin or Ó Ríogáin, from Ua Riagáin. The meaning is likely to have originated in ancient Gaelic ''ri'' ...
, 1906
(Australian angelshark) * '' Squatina caillieti'' J. H. Walsh, Ebert & Compagno, 2011 (Philippines angelshark) * '' Squatina californica'' Ayres, 1859 (Pacific angelshark) * '' Squatina david'' Acero P, Tavera Vargas, Anguila-Gómez & Hernández-Beracasa, 2016 (David's angelshark) * '' Squatina dumeril'' Lesueur, 1818 (sand devil) * '' Squatina formosa'' S. C. Shen & W. H. Ting, 1972 (Taiwan angelshark) * '' Squatina guggenheim'' Marini, 1936 (angular angelshark) * '' Squatina heteroptera'' Castro-Aguirre, Espinoza-Pérez & Huidobro-Campos, 2007 (disparate angelshark) * '' Squatina japonica'' Bleeker, 1858 (Japanese angelshark) * '' Squatina legnota''
Last A last is a mechanical form shaped like a human foot. It is used by shoemakers and cordwainers in the manufacture and repair of shoes. Lasts typically come in pairs and have been made from various materials, including hardwoods, cast iron ...
& W. T. White, 2008
(Indonesian angelshark) * '' Squatina mapama''
Long Long may refer to: Measurement * Long, characteristic of something of great duration * Long, characteristic of something of great length * Longitude (abbreviation: long.), a geographic coordinate * Longa (music), note value in early music mensu ...
, Ebert, Tavera, Pizarro, and
Robertson Robertson may refer to: People * Robertson (surname) (includes a list of people with this name) * Robertson (given name) * Clan Robertson, a Scottish clan * Robertson, stage name of Belgian magician Étienne-Gaspard Robert (1763–1837) Place ...
, 2021
(Small-crested angelshark) * '' Squatina mexicana'' Castro-Aguirre, Espinoza-Pérez & Huidobro-Campos, 2007 (Mexican angelshark) * '' Squatina nebulosa''
Regan The family name Regan, along with its cognates O'Regan, O Regan, Reagan, and O'Reagan, is an Anglicized form of the Irish surname Ó Riagáin or Ó Ríogáin, from Ua Riagáin. The meaning is likely to have originated in ancient Gaelic ''ri'' ...
, 1906
(clouded angelshark) * '' Squatina occulta'' Vooren & K. G. da Silva, 1992 (hidden angelshark) * ''
Squatina oculata The smoothback angelshark (''Squatina oculata'') is an angelshark of the family (biology), family Squatinidae found in the eastern Atlantic and Mediterranean Sea, Mediterranean. Description The smoothback angelshark can reach a length of up to 1 ...
'' Bonaparte, 1840 (smoothback angelshark) * '' Squatina pseudocellata''
Last A last is a mechanical form shaped like a human foot. It is used by shoemakers and cordwainers in the manufacture and repair of shoes. Lasts typically come in pairs and have been made from various materials, including hardwoods, cast iron ...
& W. T. White, 2008
(western angelshark) * '' Squatina punctata'' Marini 1936 * '' Squatina squatina'' (
Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...
,
1758 Events January–March * January 1 – Swedish biologist Carl Linnaeus (Carl von Linné) publishes in Stockholm the first volume (''Animalia'') of the 10th edition of ''Systema Naturae'', the starting point of modern zoologi ...
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(angelshark) * '' Squatina tergocellata'' McCulloch, 1914 (ornate angelshark) * '' Squatina tergocellatoides'' J. S. T. F. Chen, 1963 (ocellated angelshark) * '' Squatina varii'' Vaz & Carvalho, 2018 (Brazilian angelshark) Image:Squatina australis.jpg, '' Squatina australis'' Image:Squatina californica.jpg, '' Squatina californica'' Image:Squatina dumeril.jpg, '' Squatina dumeril'' Image:Squatina japonica3.jpg, '' Squatina japonica'' Image:Squatina squatina tenerife2.jpg, '' Squatina squatina''


See also

*
List of sharks Shark is the naming term of all members of Selachimorpha suborder in the subclass Elasmobranchii, in the class Chondrichthyes. The Elasmobranchii also include rays and skates; the Chondrichthyes also include Chimaeras. The first shark-like chond ...
*
List of prehistoric cartilaginous fish This list of prehistoric cartilaginous fish genera is an attempt to create a comprehensive listing of all genera that have ever been included in the class chondrichthyes ''and'' are known from the fossil record. This list excludes purely vernacul ...


References

{{Authority control Ovoviviparous fish Oxfordian first appearances Extant Late Jurassic first appearances Taxa named by André Marie Constant Duméril