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''Cephaloscyllium'' is a genus of catsharks, and part of the family Scyliorhinidae, commonly known as swellsharks because of their ability to inflate their bodies with water or air as a defense against predators. These sluggish, bottom-dwelling sharks are found widely in the tropical and temperate coastal waters of the Indian and Pacific Oceans. They have stocky, spindle-shaped bodies and short, broad, and flattened heads. The mouth is capacious, containing many small teeth and lacking furrows at the corners. The two dorsal fins are placed far back on the body, with the first much larger than the second. Different species have various color patterns of saddles, blotches, reticulations, and/or spots. The largest members of the genus can grow over in length. Swellsharks prey on a variety of fishes and invertebrates, and are
oviparous Oviparous animals are animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, most reptiles, and all pterosaurs, dinosaurs (including birds), and ...
, with females producing egg capsules in pairs. They are harmless and have been deemed of having no commercial value.


Taxonomy

The genus ''Cephaloscyllium'' was proposed by American
ichthyologist Ichthyology is the branch of zoology devoted to the study of fish, including bony fish ( Osteichthyes), cartilaginous fish (Chondrichthyes), and jawless fish (Agnatha). According to FishBase, 33,400 species of fish had been described as of Octobe ...
Theodore Gill from the Greek ''kephale'' ("head") and ''skylion'' ("dogfish"), in an 1862 issue of ''Annals of the Lyceum of Natural History of New York''. However, most of Gill's contemporaries, particularly those in Europe, preferred to keep the swellsharks within the genus ''Scyllium'' (a
synonym A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...
of '' Scyliorhinus''). ''Cephaloscyllium'' did not gain wide acceptance until
Samuel Garman Samuel Walton Garman (June 5, 1843 – September 30, 1927), or "Garmann" as he sometimes styled himself, was a naturalist/zoologist from Pennsylvania. He became noted as an ichthyologist and herpetologist. Biography Garman was born in Indian ...
published "The Plagiostomia" in a 1913 volume of ''Memoirs of the Museum of Comparative Zoology'', in which he recognized three species: '' C. isabellum'', '' C. ventriosum'', and '' C. umbratile''. A long history of taxonomic confusion exists regarding the species within ''Cephaloscyllium'' owing to several factors, including variation in appearance (particularly between juveniles and adults), the existence of multiple undescribed species, a paucity of detailed scientific descriptions and
type material In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes the ...
, and the use of unreliable characters. Until recently, various authors had recognized five to eight species, along with at least five undescribed species in Australian waters and more in the western central Pacific and the Indian Ocean. In 2008, significant studies were made in resolving the taxonomy of ''Cephaloscyllium'', with a revision of the genus and an increase in the number of described species to 21.


Species

There are currently 17 recognized species in this genus: * ''
Cephaloscyllium albipinnum The whitefin swellshark (''Cephaloscyllium albipinnum'') is a little-known species of catshark, belonging to the family (biology), family Catshark, Scyliorhinidae, Endemism, endemic to southeastern Australia. It is found down, on the outer cont ...
'' Last, Motomura &
W. T. White W. may refer to: * SoHo (Australian TV channel) (previously W.), an Australian pay television channel * ''W.'' (film), a 2008 American biographical drama film based on the life of George W. Bush * "W.", the fifth track from Codeine's 1992 EP ''Bar ...
, 2008
(whitefin swellshark) * '' Cephaloscyllium cooki'' Last, Séret &
W. T. White W. may refer to: * SoHo (Australian TV channel) (previously W.), an Australian pay television channel * ''W.'' (film), a 2008 American biographical drama film based on the life of George W. Bush * "W.", the fifth track from Codeine's 1992 EP ''Bar ...
, 2008
(Cook's swellshark) * '' Cephaloscyllium fasciatum'' W. L. Y. Chan, 1966 (reticulated swellshark) * ''
Cephaloscyllium hiscosellum The Australian reticulate swellshark (''Cephaloscyllium hiscosellum'') is a little-known species of catshark in the family Scyliorhinidae. It is found off the coast of northwestern Australia at depths of . This shark has a stocky body and a sho ...
''
W. T. White W. may refer to: * SoHo (Australian TV channel) (previously W.), an Australian pay television channel * ''W.'' (film), a 2008 American biographical drama film based on the life of George W. Bush * "W.", the fifth track from Codeine's 1992 EP ''Bar ...
& Ebert, 2008
(Australian reticulate swellshark) * '' Cephaloscyllium isabellum'' Bonnaterre, 1788 (draughtsboard shark) * ''
Cephaloscyllium laticeps The Australian swellshark (''Cephaloscyllium laticeps'') or draughtboard shark, is a species of catshark, and part of the family Scyliorhinidae, endemic to southern Australia. This bottom-dwelling species can be found on the continental sh ...
'' A. H. A. Duméril, 1853 (Australian swellshark) * '' Cephaloscyllium pictum'' Last, Séret &
W. T. White W. may refer to: * SoHo (Australian TV channel) (previously W.), an Australian pay television channel * ''W.'' (film), a 2008 American biographical drama film based on the life of George W. Bush * "W.", the fifth track from Codeine's 1992 EP ''Bar ...
, 2008
(painted swellshark) * '' Cephaloscyllium sarawakensis'' Ka. Yano, A. Ahmad & Gambang, 2005 (Sarawak pygmy swellshark) * '' Cephaloscyllium signourum'' Last, Séret &
W. T. White W. may refer to: * SoHo (Australian TV channel) (previously W.), an Australian pay television channel * ''W.'' (film), a 2008 American biographical drama film based on the life of George W. Bush * "W.", the fifth track from Codeine's 1992 EP ''Bar ...
, 2008
(flagtail swellshark) * '' Cephaloscyllium silasi'' Talwar, 1974 (Indian swellshark) * '' Cephaloscyllium speccum'' Last, Séret &
W. T. White W. may refer to: * SoHo (Australian TV channel) (previously W.), an Australian pay television channel * ''W.'' (film), a 2008 American biographical drama film based on the life of George W. Bush * "W.", the fifth track from Codeine's 1992 EP ''Bar ...
, 2008
(speckled swellshark) * '' Cephaloscyllium stevensi'' E. Clark & J. E. Randall, 2011 (Steven's swellshark) * '' Cephaloscyllium sufflans''
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'' ...
, 1921
(balloon shark) * '' Cephaloscyllium umbratile'' D. S. Jordan & Fowler, 1903 (blotchy swellshark) * '' Cephaloscyllium variegatum'' Last, Séret &
W. T. White W. may refer to: * SoHo (Australian TV channel) (previously W.), an Australian pay television channel * ''W.'' (film), a 2008 American biographical drama film based on the life of George W. Bush * "W.", the fifth track from Codeine's 1992 EP ''Bar ...
, 2008
(saddled swellshark) * '' Cephaloscyllium ventriosum'' Garman, 1880 (swellshark) * '' Cephaloscyllium zebrum'' Last, Séret &
W. T. White W. may refer to: * SoHo (Australian TV channel) (previously W.), an Australian pay television channel * ''W.'' (film), a 2008 American biographical drama film based on the life of George W. Bush * "W.", the fifth track from Codeine's 1992 EP ''Bar ...
, 2008
(narrowbar swellshark) * ''Cephaloscyllium'' sp. 1 Not yet described (Philippine swellshark) * ''Cephaloscyllium'' sp. not yet described (tiger swellshark) * ''Cephaloscyllium'' sp. not yet described (New Guinea swellshark) * ''Cephaloscyllium'' sp. not yet described (dwarf balloon shark) * ''Cephaloscyllium'' sp. not yet described (dwarf oriental swellshark) * ''Cephaloscyllium'' sp. not yet described (New Caledonia swellshark) * ''Cephaloscyllium'' sp. not yet described (Red Sea swellshark)


Phylogeny and evolution

Morphological and
molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...
studies have shown the closest relative of ''Cephaloscyllium'' to be ''Scyliorhinus'', and these two genera and '' Poroderma'' form the
subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end subfamily botanical names with "-oideae", and zoologi ...
Scyliorhininae, the most
basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is nec ...
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
of the
order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...
Carcharhiniformes. The oldest confirmed ''Cephaloscyllium'' fossils come from Miocene epoch (23–5.3
Mya Mya may refer to: Brands and product names * Mya (program), an intelligent personal assistant created by Motorola * Mya (TV channel), an Italian Television channel * Midwest Young Artists, a comprehensive youth music program Codes * Burmese ...
) deposits in California, though based on the rate of DNA divergence in sharks, the swellshark lineage likely dates back to the Cretaceous period (145.5–65.5 Mya).


Distribution and habitat

''Cephaloscyllium'' is widely distributed in the Indian and Pacific Oceans, in temperate and tropical waters, but not close to the
equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can als ...
. Swellshark diversity is greatest around
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
and in the west-central Pacific, where multiple endemic species are found. The most far-flung members of the genus are ''C. sufflans'' off southeastern Africa, ''C. silasi'' off southwestern India, ''C. umbratile'' in the northwestern Pacific, and ''C. ventriosum'' along the western coast of the
Americas The Americas, which are sometimes collectively called America, are a landmass comprising the totality of North and South America. The Americas make up most of the land in Earth's Western Hemisphere and comprise the New World. Along with th ...
. One hypothesis states ''Cephaloscyllium'' originally evolved in Australia and New Guinea, and subsequently dispersed outwards in a series of colonization events, eventually reaching Africa and the Americas. ''Cephaloscyllium'' species, bottom-dwelling sharks, can be found from the
intertidal zone The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species o ...
to a depth of on upper continental and insular slopes.


Description

Swellsharks are stocky and spindle shaped, with the trunk tapering substantially to the caudal peduncle. The head is short (comprising less than a fifth of the total length), broad, and flattened. The snout is very short and blunt, with the nostrils preceded by laterally enlarged flaps of skin. The eyes are horizontally oval or slit-like and placed high on the head, with cat-like pupils and rudimentary nictitating eyelids. A broad ridge occurs beneath each eye, and a
spiracle Spiracle or spiraculum may refer to: * Spiracle (arthropods), opening in the exoskeletons of some arthropods * Spiracle (vertebrates), openings on the surface of some vertebrates * Spiraculum, a genus of land snails in family Cyclophoridae Cycl ...
behind. The mouth is very large and wide, containing numerous small, multicusped teeth; the upper teeth are exposed when the mouth is closed (except in ''C. silasi''). No furrows are found at the corners of the mouth. The pectoral fins are generally large and broad, and the
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 en ...
s are small. The two dorsal fins are placed far back on the body: the first dorsal fin originates behind the
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 en ...
origins, while the second dorsal fin is positioned about opposite the
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 se ...
. The first dorsal and anal fins are much larger than the second dorsal fin. The tail is short; the caudal fin is broad with a distinct lower lobe and a strong ventral notch near the tip of the upper lobe. The skin is thick and covered by well- calcified
dermal denticle A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scales, which can also provide effective camouflage through the use of reflection and colouration, as we ...
s. The coloration is typically grayish or brownish, with a variety of patterns that include saddles, blotches, reticulations, and/or spots. In several species, the juveniles differ substantially in coloration from the adults. ''Cephaloscyllium'' species generally fall into two size groups: dwarf species include ''C. fasciatum'' and ''C. silasi'', which are under long, and large species include ''C. umbratile'' and ''C. ventriosum'', which may exceed in length.


Biology and ecology

Members of the genus ''Cephaloscyllium'' are generally slow-moving, sedentary animals with an anguilliform ( eel-like) mode of swimming. Of the species whose diets have been documented, they have been known to feed on a wide variety of benthic organisms, including other sharks and rays,
bony fish Osteichthyes (), popularly referred to as the bony fish, is a diverse superclass of fish that have skeletons primarily composed of bone tissue. They can be contrasted with the Chondrichthyes, which have skeletons primarily composed of cartilag ...
es, crustaceans, and
mollusc 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 esti ...
s. Swellsharks are perhaps best known for their ability to inflate themselves by rapidly swallowing water or air when threatened; this behavior may allow them to wedge themselves inside crevices, make themselves harder to swallow, and/or intimidate a would-be predator. Reproduction is
oviparous Oviparous animals are animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, most reptiles, and all pterosaurs, dinosaurs (including birds), and ...
, with females producing two eggs at a time, one in each oviduct. Individual eggs are enclosed in a flask-shaped capsules with tendrils at the corners that allow them to be attached to underwater structures.


Human interactions

Swellsharks are harmless to humans and generally of no economic value, but are susceptible to being caught as
bycatch Bycatch (or by-catch), in the fishing industry, is a fish or other marine species that is caught unintentionally while fishing for specific species or sizes of wildlife. Bycatch is either the wrong species, the wrong sex, or is undersized or juve ...
in artisanal and commercial fisheries. Several species (e.g. ''C. umbratile'' and ''C. ventriosum''), are known to be extremely hardy, capable of surviving out of water for extended periods and adapting readily to captivity.


References

{{Taxonbar, from=Q2510308 Shark genera Taxa named by Theodore Gill