Cephaloscyllium
Encyclopedia
Cephaloscyllium is a genus
of catshark
, family
Scyliorhinidae, commonly known as swellsharks because of their ability to inflate their body 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 Ocean
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
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 1 m (3.3 ft) in length. Swellsharks prey on a variety of fishes and invertebrate
s, and are oviparous with females producing egg capsules in pairs. They are harmless and of no commercial value.
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
of Scyliorhinus
). Cephaloscyllium did not gain wide acceptance until Samuel Garman 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.
There is a long history of taxonomic confusion 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 5–8 species, along with at least 5 undescribed species in Australian waters and more in the western central Pacific and the Indian Ocean. In 2008, significant strides were made in resolving the taxonomy of Cephaloscyllium, with a revision of the genus and an increase in the number of described species to 19.
and molecular phylogenetic studies have determined that the closest relative of Cephaloscyllium is Scyliorhinus, and that these two genera and Poroderma
form the subfamily Scyliorhininae, the most basal
clade
of the order
Carcharhiniformes
. The oldest confirmed Cephaloscyllium fossil
s come from Miocene
epoch
(23.0–5.3 Ma) 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 Ma).
and tropical waters but not close to the equator
. Swellshark diversity is greatest around Australia
and in the western central Pacific, where there are multiple endemic species. 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
. One hypothesis
is that 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 are bottom-dwelling sharks that can be found from the intertidal zone
to a depth of 670 m (2,198.2 ft) on upper continental and insular slopes.
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
s and rudimentary nictitating eyelids. There is a broad ridges beneath each eye, and a spiracle
behind. The mouth is very large and wide, containing numerous small, multi-cusped teeth; the upper teeth are exposed when the mouth is closed (except in C. silasi
). There are no furrows at the corners of the mouth.
The pectoral fins are generally large and broad, and the pelvic fins are small. The two dorsal fin
s are placed far back on the body: the first dorsal fin originates behind the pelvic fin origins, while the second dorsal fin is positioned about opposite the anal fin. 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 denticles. 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 50 cm (19.7 in) long, and large species include C umbratile and C. ventriosum
, which may exceed 1 m (3.3 ft) in length.
-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 fishes, crustacean
s, and molluscs. 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, with females producing eggs two 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.
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.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of catshark
Catshark
Catsharks are ground sharks of the family Scyliorhinidae, with over 150 known species. While they are generally known as catsharks, many species are commonly called dogfish....
, family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Scyliorhinidae, commonly known as swellsharks because of their ability to inflate their body with water or air as a defense against predators. These sluggish, bottom-dwelling sharks are found widely in the tropical and temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
coastal waters of the Indian
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
and Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
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
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
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 1 m (3.3 ft) in length. Swellsharks prey on a variety of fishes and invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s, and are oviparous with females producing egg capsules in pairs. They are harmless and of no commercial value.
Taxonomy
The genus Cephaloscyllium was proposed by American ichthyologist Theodore GillTheodore Gill
Theodore Nicholas Gill was an American ichthyologist, mammalogist, malacologist and librarian.Born and educated in New York City under private tutors, Gill early showed interest in natural history. He was associated with J...
from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
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
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, preferred to keep the swellsharks within the genus Scyllium (a synonym
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
of Scyliorhinus
Scyliorhinus
Scylorhinus is a genus of catsharks in the family Scyliorhinidae.-Species:* Scyliorhinus besnardi S. Springer & Sadowsky, 1970 * Scyliorhinus boa Goode & Bean, 1896...
). Cephaloscyllium did not gain wide acceptance until Samuel Garman published "The Plagiostomia" in a 1913 volume of Memoirs of the Museum of Comparative Zoology, in which he recognized three species: C. isabellum
Draughtsboard shark
The draughtsboard shark is a species of catshark, family Scyliorhinidae, so named for its "checkerboard" color pattern of dark blotches. It is endemic to New Zealand, where it is also known as the carpet shark...
, C. ventriosum
Swellshark
The swellshark, Cephaloscyllium ventriosum, is a catshark of the family Scyliorhinidae. It is found in the subtropical eastern Pacific Ocean between latitudes 40° N and 37° S, from the surface to 460 m....
, and C. umbratile.
There is a long history of taxonomic confusion 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 5–8 species, along with at least 5 undescribed species in Australian waters and more in the western central Pacific and the Indian Ocean. In 2008, significant strides were made in resolving the taxonomy of Cephaloscyllium, with a revision of the genus and an increase in the number of described species to 19.
Phylogeny and evolution
MorphologicalMorphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
and molecular phylogenetic studies have determined that the closest relative of Cephaloscyllium is Scyliorhinus, and that these two genera and Poroderma
Poroderma
Poroderma is a genus of catshark, family Scyliorhinidae. The colour of these sharks are usually grey with dark stripes. They are found in South Africa and are nocturnal. They live preferably in shore areas, close to the bottom, to depths of 100 m. They prefer small caves and crevices. Their diet...
form the subfamily Scyliorhininae, the most basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
of the order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
Carcharhiniformes
Carcharhiniformes
The ground sharks, order Carcharhiniformes, are the largest order of sharks. With over 270 species, carcharhiniforms include a number of common types, such as the blue shark, catsharks, swellsharks, and sandbar shark....
. The oldest confirmed Cephaloscyllium fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s come from Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
epoch
Geologic time scale
The geologic time scale provides a system of chronologic measurement relating stratigraphy to time that is used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth...
(23.0–5.3 Ma) deposits in California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
, though based on the rate of DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
divergence in sharks the swellshark lineage likely dates back to the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
period
Geologic time scale
The geologic time scale provides a system of chronologic measurement relating stratigraphy to time that is used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth...
(145.5–65.5 Ma).
Distribution and habitat
Cephaloscyllium is widely distributed in the Indian and Pacific Oceans, in temperateTemperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
and tropical waters but not close to the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
. Swellshark diversity is greatest around Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
and in the western central Pacific, where there are multiple endemic species. The most far-flung members of the genus are C. sufflans
Balloon shark
The balloon shark is a species of catshark, family Scyliorhinidae, endemic to the southwestern Indian Ocean off South Africa and Mozambique. Benthic in nature, it is found over sandy and muddy flats at depths of...
off southeastern Africa, C. silasi
Indian swellshark
The Indian swellshark, Cephaloscyllium silasi, is a catshark of the family Scyliorhinidae found in the western Indian Ocean from Quilon, India and Sauqira Bay, Oman between latitudes 16° N and 10° N, from the surface to 300 m. It grows to about 36 cm in length, and can expand its body by...
off southwestern India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, C. umbratile in the northwestern Pacific, and C. ventriosum
Swellshark
The swellshark, Cephaloscyllium ventriosum, is a catshark of the family Scyliorhinidae. It is found in the subtropical eastern Pacific Ocean between latitudes 40° N and 37° S, from the surface to 460 m....
along the western coast of the Americas
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...
. One hypothesis
Hypothesis
A hypothesis is a proposed explanation for a phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose". For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...
is that Cephaloscyllium originally evolved in Australia and New Guinea
New Guinea
New Guinea is the world's second largest island, after Greenland, covering a land area of 786,000 km2. Located in the southwest Pacific Ocean, it lies geographically to the east of the Malay Archipelago, with which it is sometimes included as part of a greater Indo-Australian Archipelago...
, and subsequently dispersed outwards in a series of colonization events, eventually reaching Africa and the Americas. Cephaloscyllium species are bottom-dwelling sharks that can be found from the intertidal zone
Intertidal zone
The intertidal zone is the area that is above water at low tide and under water at high tide . This area can include many different types of habitats, with many types of animals like starfish, sea urchins, and some species of coral...
to a depth of 670 m (2,198.2 ft) 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 nostrilNostril
A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...
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
Pupil
The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In...
s and rudimentary nictitating eyelids. There is a broad ridges beneath each eye, and a spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...
behind. The mouth is very large and wide, containing numerous small, multi-cusped teeth; the upper teeth are exposed when the mouth is closed (except in C. silasi
Indian swellshark
The Indian swellshark, Cephaloscyllium silasi, is a catshark of the family Scyliorhinidae found in the western Indian Ocean from Quilon, India and Sauqira Bay, Oman between latitudes 16° N and 10° N, from the surface to 300 m. It grows to about 36 cm in length, and can expand its body by...
). There are no furrows at the corners of the mouth.
The pectoral fins are generally large and broad, and the pelvic fins are small. The two dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
s are placed far back on the body: the first dorsal fin originates behind the pelvic fin origins, while the second dorsal fin is positioned about opposite the anal fin. 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
Calcification
Calcification is the process in which calcium salts build up in soft tissue, causing it to harden. Calcifications may be classified on whether there is mineral balance or not, and the location of the calcification.-Causes:...
dermal denticles. 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
Reticulated swellshark
The reticulated swellshark, Cephaloscyllium fasciatum, is a catshark of the family Scyliorhinidae found in the western Pacific Ocean between latitudes 21° N and 28° S, at depths of between 220 and 450 m. It grows to about 42 cm in length....
and C. silasi
Indian swellshark
The Indian swellshark, Cephaloscyllium silasi, is a catshark of the family Scyliorhinidae found in the western Indian Ocean from Quilon, India and Sauqira Bay, Oman between latitudes 16° N and 10° N, from the surface to 300 m. It grows to about 36 cm in length, and can expand its body by...
, which are under 50 cm (19.7 in) long, and large species include C umbratile and C. ventriosum
Swellshark
The swellshark, Cephaloscyllium ventriosum, is a catshark of the family Scyliorhinidae. It is found in the subtropical eastern Pacific Ocean between latitudes 40° N and 37° S, from the surface to 460 m....
, which may exceed 1 m (3.3 ft) in length.
Biology and ecology
Members of the genus Cephaloscyllium are generally slow-moving, sedentary animals with an anguilliform (eelEel
Eels are an order of fish, which consists of four suborders, 20 families, 111 genera and approximately 800 species. Most eels are predators...
-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 fishes, crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s, and molluscs. 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, with females producing eggs two at a time, one in each oviduct
Oviduct
In non-mammalian vertebrates, the passageway from the ovaries to the outside of the body is known as the oviduct. The eggs travel along the oviduct. These eggs will either be fertilized by sperm to become a zygote, or will degenerate in the body...
. 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 bycatchBycatch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...
in artisanal
Artisan fishing
Artisan fishing is a term used to describe small scale low-technology commercial or subsistence fishing practices. The term particularly applies to coastal or island ethnic groups using traditional techniques such as rod and tackle, arrows and harpoons, throw nets and drag nets, and traditional...
and commercial fisheries
Commercial fishing
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 pursue fish far into the ocean under adverse conditions...
. 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.