''Cephaloscyllium'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of catsharks, and part of the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Scyliorhinidae Scyliorhinidae is a Family (biology), family of sharks, one of a few families whose members share the common name catsharks, belonging to the Order (biology), order Carcharhiniformes, the ground sharks. Although they are generally known as cats ...

, commonly known as swellsharks because of their ability to inflate their bodies with water or air as a defense against

predator Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...

s. These sluggish, bottom-dwelling sharks are found widely in the

tropical The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...

and

temperate In geography, the temperate climates of Earth occur in the middle latitudes (approximately 23.5° to 66.5° N/S of the Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ran ...

coastal waters of the Indian and

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...

s. 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 fin A dorsal fin is a fin on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...

s 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

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

s, and are

oviparous Oviparous animals are animals that reproduce by depositing fertilized zygotes outside the body (i.e., by laying or spawning) in metabolically independent incubation organs known as eggs, which nurture the embryo into moving offsprings kno ...

, 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, 35,800 species of fish had been described as of March 2 ...

Theodore Gill Theodore Nicholas Gill (March 21, 1837 – September 25, 1914) was an American ichthyologist, mammalogist, malacologist, and librarian. Career Born and educated in New York City under private tutors, Gill early showed interest in natural hist ...

from the

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

''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 precisely 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 a ...

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 an American naturalist and zoologist. He became noted as an ichthyologist and herpetologist. Biography Garman was born in Indiana Co ...

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, 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.

Description

Swellsharks are stocky and spindle shaped, with the trunk tapering substantially to the

caudal peduncle Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...

. The head is short (constituting less than a fifth of the total length), broad, and flattened. The snout is very short and blunt, with the

nostril A nostril (or naris , : nares ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbinates ...

s preceded by laterally enlarged flaps of skin. The eyes are horizontally oval or slit-like and placed high on the head, with cat-like

pupil The pupil is a hole located in the center of the iris of the eye that allows light to strike the retina.Cassin, B. and Solomon, S. (1990) ''Dictionary of Eye Terminology''. Gainesville, Florida: Triad Publishing Company. It appears black becau ...

s and rudimentary nictitating eyelids. A broad ridge occurs beneath each eye, and a spiracle 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 fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish aquatic locomotion, swim. Apart from the tail or caudal fin, fish fins have no direct connection with the vertebral column ...

s are generally large and broad, while the

pelvic fin Pelvic fins or ventral fins are paired fins located on the ventral (belly) surface of fish, and are the lower of the only two sets of paired fins (the other being the laterally positioned pectoral fins). The pelvic fins are homologous to the hi ...

s are small. The two

s are placed far back on the body: the first dorsal fin originates behind the

origins, while the second dorsal fin is positioned about opposite the

anal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported o ...

. The first dorsal and anal fins are much larger than the second dorsal fin. The tail is short; the

caudal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...

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 scale (zoology), scales, which can also provide effective Underwater camouflage, camouflage through the us ...

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.

Distribution and habitat

''Cephaloscyllium'' is widely distributed in the Indian and Pacific Oceans, in

and

waters, but not close to the

equator The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...

. Swellshark diversity is greatest around

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

and in the west-central Pacific, where multiple

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

species are found. The most far-flung members of the genus are ''C. sufflans'' off southeastern Africa, ''C. silasi'' off southwestern

India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...

, ''C. umbratile'' in the northwestern Pacific, and ''C. ventriosum'' along the western coast of the

Americas The Americas, sometimes collectively called America, are a landmass comprising the totality of North America and South America.''Webster's New World College Dictionary'', 2010 by Wiley Publishing, Inc., Cleveland, Ohio. When viewed as a sing ...

. One

hypothesis A hypothesis (: hypotheses) is a proposed explanation for a phenomenon. A scientific hypothesis must be based on observations and make a testable and reproducible prediction about reality, in a process beginning with an educated guess o ...

states ''Cephaloscyllium'' originally evolved in Australia and

New Guinea New Guinea (; Hiri Motu: ''Niu Gini''; , fossilized , also known as Papua or historically ) is the List of islands by area, world's second-largest island, with an area of . Located in Melanesia in the southwestern Pacific Ocean, the island is ...

, 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 or foreshore is the area above water level at low tide and underwater at high tide; in other words, it is the part of the littoral zone within the tidal range. This area can include several types of habitats with various ...

to a depth of on upper continental and insular slopes.

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 ( ; ), also known as osteichthyans or commonly referred to as the bony fish, is a Biodiversity, diverse clade of vertebrate animals that have endoskeletons primarily composed of bone tissue. They can be contrasted with the Chondricht ...

es,

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s, and

mollusc Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

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

, with females producing two eggs at a time, one in each

oviduct The oviduct in vertebrates is the passageway from an ovary. In human females, this is more usually known as the fallopian tube. The eggs travel along the oviduct. These eggs will either be fertilized by spermatozoa to become a zygote, or will dege ...

. Individual eggs are enclosed in a flask-shaped capsules with tendrils at the corners that allow them to be attached to underwater structures. It has recently been documented that ''Cephaloscyllium'' can generate new organisms through parthenogenesis, which is a natural process that allows organisms to reproduce asexually, without fertilization.Feldheim, K. A., et al. "Multiple births by a captive swellshark C ephaloscyllium ventriosum via facultative parthenogenesis." ''Journal of Fish Biology'' 90.3 (2017): 1047-1053.

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 botanical subfamily names with "-oideae", and zo ...

Scyliorhininae, the most basal

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

of the

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

Carcharhiniformes. The oldest confirmed ''Cephaloscyllium''

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

s come from

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided b ...

(23–5.3 Mya) deposits in

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

, though based on the rate of

DNA Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...

divergence in sharks, the swellshark lineage likely dates back to the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

period (145.5–65.5 Mya).

Species

There are currently 17 recognized species in this genus: * '' Cephaloscyllium albipinnum''

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 come in many styles and sizes, depending on the exact job they are designed for. Common variations ...

, Motomura & W. T. White, 2008 (whitefin swellshark) * '' Cephaloscyllium cooki''

, Séret & W. T. White, 2008 (Cook's swellshark) * '' Cephaloscyllium fasciatum'' W. L. Y. Chan, 1966 (reticulated swellshark) * '' Cephaloscyllium hiscosellum'' W. T. White & Ebert, 2008 (Australian reticulate swellshark) * '' Cephaloscyllium isabellum'' Bonnaterre, 1788 (draughtsboard shark) * '' Cephaloscyllium laticeps'' A. H. A. Duméril, 1853 (Australian swellshark) * '' Cephaloscyllium pictum''

, Séret & W. T. White, 2008 (painted swellshark) * '' Cephaloscyllium sarawakensis'' Ka. Yano, A. Ahmad & Gambang, 2005 (Sarawak pygmy swellshark) * '' Cephaloscyllium signourum''

, Séret & W. T. White, 2008 (flagtail swellshark) * '' Cephaloscyllium silasi''

Talwar The talwar (), also spelled talwaar and tulwar, is a type of curved sword or sabre from the Indian subcontinent. Etymology and classification The word ''talwar'' originated from the Sanskrit Language, Sanskrit word ''taravāri'' () which means ...

, 1974 (Indian swellshark) * '' Cephaloscyllium speccum''

, Séret & W. T. White, 2008 (speckled swellshark) * '' Cephaloscyllium stevensi'' E. Clark & J. E. Randall, 2011 (Steven's swellshark) * '' Cephaloscyllium sufflans'' Regan, 1921 (balloon shark) * '' Cephaloscyllium umbratile'' D. S. Jordan & Fowler, 1903 (blotchy swellshark) * '' Cephaloscyllium variegatum''

, Séret & W. T. White, 2008 (saddled swellshark) * '' Cephaloscyllium ventriosum'' Garman, 1880 (swellshark) * '' Cephaloscyllium zebrum''

, Séret & W. T. White, 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)

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 ...

artisanal An artisan (from , ) is a skilled craft worker who makes or creates material objects partly or entirely by hand. These objects may be functional or strictly decorative, for example furniture, decorative art, sculpture, clothing, food ite ...

and

commercial fisheries Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often p ...

. 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