Cephaloscyllium

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Cephaloscyllium
Temporal range: Miocene–Present [1]
Cephaloscyllium laticeps 1.jpg
Australian swellshark (C. laticeps)
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Order: Carcharhiniformes
Family: Scyliorhinidae
Genus: Cephaloscyllium
T. N. Gill, 1862
Type species
Scyllium laticeps
A. H. A. Duméril 1853

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 1 m (3.3 ft) in length. Swellsharks prey on a variety of fishes and invertebrates, and are oviparous, with females producing egg capsules in pairs. They are harmless and have been deemed of having no commercial value.

Contents

Taxonomy

The genus Cephaloscyllium was proposed by American ichthyologist 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. [2] [3] 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 . [2]

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. [3] 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. [3] [4] [5]

Species

There are currently 17 recognized species in this genus:

Phylogeny and evolution

Morphological and molecular phylogenetic studies have shown the closest relative of Cephaloscyllium to be Scyliorhinus, and these two genera and Poroderma form the subfamily Scyliorhininae, the most basal clade of the order Carcharhiniformes. [2] [4] The oldest confirmed Cephaloscyllium fossils come from Miocene epoch (235.3 Mya) deposits in California, [1] though based on the rate of DNA divergence in sharks, the swellshark lineage likely dates back to the Cretaceous period (145.565.5 Mya). [4]

Distribution and habitat

Cephaloscyllium is widely distributed in the Indian and Pacific Oceans, in temperate and tropical waters, but not close to the equator. Swellshark diversity is greatest around Australia 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. [4] 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. [4] Cephaloscyllium species, bottom-dwelling sharks, can be found from the intertidal zone to a depth of 670 m (2,200 ft) on upper continental and insular slopes. [3]

Description

Swellsharks (C. ventriosum) have broad, flattened heads and thick bodies. Swell Shark, San Clemente Island, California.jpg
Swellsharks (C. ventriosum) have broad, flattened heads and thick bodies.

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 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. [2]

The pectoral fins are generally large and broad, and the pelvic fins are small. The two dorsal fins 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. [2] 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 (20 in) long, and large species include C. umbratile and C. ventriosum, which may exceed 1 m (3.3 ft) in length. [4]

Biology and ecology

Members of the genus Cephaloscyllium are generally slow-moving, sedentary animals with an anguilliform (eel-like) mode of swimming. [4] 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, crustaceans, and molluscs. [6] 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 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. [2]

Human interactions

Swellsharks are harmless to humans and generally of no economic value, but are susceptible to being caught as bycatch in artisanal and commercial fisheries. [4] 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. [6]

Related Research Articles

Catshark

Catsharks are ground sharks of the family Scyliorhinidae. They are one of the largest families of sharks with around 160 species placed in 17 genera. Although they are generally known as catsharks, many species are commonly called dogfish or gato. Like most bottom feeders, they feed on benthic invertebrates and smaller fish. Catsharks are not harmful to humans.

<i>Parmaturus</i>

Parmaturus is a genus of catshark in the family Scyliorhinidae. Four species were described in 2007 and another in 2019 with more species likely to be described in the near future.

<i>Galeus</i>

Galeus is a genus of catshark, belonging to the family Scyliorhinidae, commonly known as sawtail catsharks in reference to a distinctive saw-toothed crest of enlarged dermal denticles, found along the upper edges of their caudal fins. They are found in the Atlantic, the western and central Pacific, and the Gulf of California, inhabiting deep waters at or close to the sea floor. Members of this genus are rather small, slim sharks with firm bodies and thick, rough skin. Their heads are usually fairly long and pointed, and have large mouths with well-developed furrows at the corners. They have large pectoral and anal fins, and two similar dorsal fins placed well back. Many species are ornately patterned with dark saddles and/or blotches. Sawtail catsharks feed on various invertebrates and fishes, and may be either egg-laying or live-bearing. These harmless sharks are sometimes caught as bycatch but are of minimal commercial value.

Draughtsboard shark

The draughtsboard shark is a species of catshark, and part of the 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. This shark typically reaches 1 m (3.3 ft) in length and has a thick body with a broad, flattened head and a capacious mouth. Its two dorsal fins are placed far back on the body, with the first much larger than the second.

Australian swellshark

The Australian swellshark 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 shelf down to a depth of 220 m (720 ft). Usually measuring 1 m (3 ft) long, it is a stout-bodied, broad-headed shark with a short tail and a first dorsal fin much larger than the second. It can be identified by its variegated dorsal coloration of brown or gray patches and numerous spots.

Indian swellshark

The Indian swellshark 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 taking in air or water to make it appear larger to predators.

Balloon shark

The balloon shark is a species of catshark, and part of the 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 40–600 m (130–1,970 ft). This thick-bodied species has a broad, flattened head and a short tail; its distinguishing traits include narrow, lobe-like skin flaps in front of the nostrils, and a dorsal color pattern of faint darker saddles on a light grayish background.

Blotchy swellshark

The blotchy swellshark, or Japanese swellshark, is a common species of catshark, belonging to the family Scyliorhinidae. The Blotchy swellshark is found at depths of 90–200 m (300–660 ft) in the northwestern Pacific Ocean, from Japan to Taiwan. It is benthic in nature and favors rocky reefs. Reaching 1.4 m (4.6 ft) in length, this thick-bodied shark has a broad head, large mouth, and two unequally-sized dorsal fins positioned far back past the pelvic fins. It can be identified by its dorsal coloration, consisting of seven brown "saddles" and extensive darker mottling on a light tan background. This species has often been confounded with the draughtsboard shark and the Sarawak pygmy swellshark in scientific literature.

Northern sawtail catshark

The northern sawtail catshark is a little-known species of catshark, and part of the family Scyliorhinidae, endemic to northeastern Australia. It is demersal in nature and inhabits the upper continental slope at a depth of 300–420 m (980–1,380 ft). A small, slender species growing no longer than 42 cm (17 in), the northern sawtail catshark is characterized by a series of dark, narrow saddles along its back and tail, and rows of prominently enlarged dermal denticles along the upper edge of its caudal fin and the underside of its caudal peduncle. The International Union for Conservation of Nature (IUCN) does not yet have enough information to assess its conservation status.

The whitefin swellshark is a little-known species of catshark, belonging to the family Scyliorhinidae, endemic to southeastern Australia. It is found 126–554 m (413–1,818 ft) down, on the outer continental shelf and upper continental slope. Reaching 1.1 m (3.6 ft) in length, this shark has a very thick body and a short, broad, flattened head with a large mouth. It is characterized by a dorsal color pattern of dark saddles and blotches over a brown to gray background, and light fin margins. When threatened the whitefin swellshark can inflate itself with water or air to increase its size. Reproduction is oviparous. As of 2019 The International Union for Conservation of Nature(IUCN) has assessed this species as Critically Endangered due to the significant decline of the population.

The saddled swellshark is a rare species of catshark, and part of the family Scyliorhinidae, endemic to Eastern Australia. This bottom-dwelling species is found on the outer continental shelf and upper continental slope at a depth of 115–605 m (377–1,985 ft). It is a robustly built shark with a short, broad, flattened head and a capacious mouth. Adults are patterned with saddles on a brownish or grayish background, which varies between tropical and temperate sharks; juveniles are light-colored with many spots. This shark reaches 74 cm (29 in) in length. Like other swellsharks, it can inflate itself as a defensive measure. Reproduction is oviparous.

The narrowbar swellshark is a rare species of catshark, and part of the family Scyliorhinidae, known only from two specimens collected near Flinders Reef off northeastern Australia. This species reaches at least 44.5 cm (17.5 in) in length, and has a stocky body with a short, broad head. It can be readily identified by its zebra-like dorsal color pattern of transverse brown bars on a yellowish background. Like other swellsharks, it can inflate its body as a defensive measure.

The speckled swellshark is a little-known species of catshark, and part of the family Scyliorhinidae, endemic to the waters off northwestern Australia. It occurs on the outer continental shelf and upper continental slope, at a depth of 150–455 m (492–1,493 ft). This species grows to 69 cm (27 in) long and has a stocky body and a short, broad, flattened head. As its common name suggests, its color pattern consists of many dark spots and white-spotted dark saddles and blotches on a light gray background. The juveniles are yellow with dark spots and lines, and a distinctive eyespot-like mark behind each eye. Like other swellsharks, this species can inflate itself as a defensive measure.

The Cook's swellshark is a little-known species of catshark, belonging to the family Scyliorhinidae. This shark is found in the Arafura Sea at a depth of 223–300 m (732–984 ft). It is a stocky-bodied shark with a short, broad head and a large mouth, and can be identified by the eight dark, pale-edged saddles along its grayish brown body and tail. The maximum known length of this species is 30 cm (12 in). Like other swellsharks, it can inflate itself with water or air when threatened.

Australian reticulate swellshark

The Australian reticulate swellshark is a little-known species of catshark in the family Scyliorhinidae. It is found off the coast of northwestern Australia at depths of 290–420 m (950–1,380 ft). This shark has a stocky body and a short, wide head with a capacious mouth. It is characterized by a striking dorsal color pattern of dark brown lines that trace a series of hollow saddles and narrow rings, on a light background. Like other swellsharks, this species can inflate itself when threatened. Its reproduction is oviparous.

The painted swellshark is a little-known species of catshark, belonging to the family Scyliorhinidae, found in eastern Indonesia. This species reaches a maximum known length of 72 cm (28 in), and has a thick body with a short, broad and flattened head. It is dark gray with a variegated pattern of irregular darker and lighter blotches above, and lighter below with gray blotches and speckling on the snout. Like other swellsharks, it can inflate itself as a defensive measure.

The flagtail swellshark is a little-known species of catshark, belonging to the family Scyliorhinidae, found at a depth of 480–700 m (1,570–2,300 ft) off northeastern Queensland, and possibly also nearby islands. This stout-bodied shark has a short, broad, and flattened head with a capacious mouth. Adults have a variegated brown coloration with 9–10 darker dorsal saddles and "V"-shaped blotch at the tip of the upper caudal fin lobe. Juveniles are yellow with narrow brown bars instead of saddles, and a distinctive marking between the spiracles shaped like two loops connected by a line. Like other swellsharks, this species can inflate its body when threatened.

Figaro is a genus of catshark, and part of the family Scyliorhinidae. Until 2008, Figaro was generally considered to be a subgenus of Galeus. The two known species are found off Australia, inhabiting deep, offshore waters on or near the bottom. Figaro contains small, slender, firm-bodied sharks that bear distinctive crests of enlarged, spiny dermal denticles along the dorsal and ventral edges of their short caudal fins. The caudal peduncle is relatively long, such as that the anal and caudal fins are some distance apart. In adult males, the inner margins of the pelvic fins are fused together to form a subtle "apron" over the claspers. F. boardmani is a predator of fishes, crustaceans, and cephalopods, and is oviparous; less is known about the F. striatus. Both are harmless and are of no economic importance.

References

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  3. 1 2 3 4 Schaaf-Da Silva, J.A. and D.A. Ebert (September 8, 2008). "A revision of the western North Pacific swellsharks, genus Cephaloscyllium Gill 1862 (Chondrichthyes: Carcharhiniformes: Scyliorhinidae), including descriptions of two new species". Zootaxa1872: 18.
  4. 1 2 3 4 5 6 7 8 Schaaf-Da Silva, J.A. (December 2007). A Taxonomic Revision of the North Pacific Swell Sharks, Genus Cephaloscyllium. M.Sc. Thesis, San José State University.
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