Wobbegong is the common name given to the 12 species of carpet shark in the family Orectolobidae. They are found in shallow temperate and tropical waters of the western Pacific Ocean and eastern Indian Ocean, chiefly around Australia and Indonesia, although one species (the Japanese wobbegong, Orectolobus japonicus) occurs as far north as Japan.

The word wobbegong is thought to come from an Australian Aboriginal language and means shaggy beard, referring to the growths around the mouth of the shark.

Wobbegongs are bottom-dwelling sharks, spending much of their time resting on the sea floor. Most species have a maximum length of 1.25 m, but the largest, the spotted wobbegong, Orectolobus maculatus, and banded wobbegong, Orectolobus halei, reach about 3 m in length.

Wobbegongs are well camouflaged by a symmetrical pattern of bold markings resembling a carpet. Because of this striking pattern, wobbegongs and their close relatives are often referred to as carpet sharks.

The camouflage is improved by the presence of small, weed-like whisker lobes surrounding the wobbegong’s jaw, which help to camouflage it and act as sensory barbs. Wobbegongs make use of their camouflage to hide among rocks and catch smaller fish that swim too close, typical of ambush predators. Wobbegongs also have powerful jaws with needle-like teeth to assist in catching reef fish and other sharks for food. The blood cells of several species of wobbegongs have been described.

Wobbegongs are generally not considered dangerous to humans but have attacked swimmers, snorkelers, and scuba-divers, who inadvertently come close to them. The Australian Shark Attack File contains more than 50 records of unprovoked attacks by wobbegongs and the International Shark Attack File has 31 records, none of them fatal. Wobbegongs have also bitten surfers. Wobbegongs are very flexible and can easily bite a hand holding their tail. They have many small but sharp teeth and their bite can be severe, even through a wetsuit; having bitten, they have been known to hang on and can be very difficult to remove.

The Hemiscylliidae are a family of sharks in the order Orectolobiformes, commonly known as longtail carpet sharks and sometimes bamboo sharks. They are found in shallow waters of the tropical Indo-Pacific.

They are relatively small sharks, with the largest species reaching no more than 121 cm in adult body length. They have elongated, cylindrical bodies, with short barbels and large spiracles. As their common name suggests, they have unusually long tails, which exceed the length of the rest of their bodies. They are sluggish fish, feeding on bottom-dwelling invertebrates and smaller fish. Bamboo sharks make noises such as popping and sucking when feeding, clicking jaws when handled as a stress signal and hissing by expelling water from their gills.

Chiloscyllium

This genus is distinguished by a relatively long snout with subterminal nostrils. The eyes and supraorbital ridges are hardly elevated. The mouth is closer to the eyes than to the tip of the snout, with lower labial folds usually connected across the chin by a flap of skin. The pectoral and pelvic fins are thin and not very muscular. No black hood on the head or large black spot on the side is present (though juveniles often are strongly marked with dark spots/bars).

Hemiscyllium

This genus is confined to tropical waters of Australia, Papua New Guinea, and Indonesia, but an individual from this genus, possibly representing an undescribed species, has been photographed at the Seychelles. They have short snouts with the nostrils placed almost at the tip, and well-elevated eyes and supraorbital ridges. The mouth is closer to the tip of the snout than the eyes, and lacks the connecting dermal fold across the chin. The pectoral and pelvic fins are thick and heavily muscular. Either a black hood on the head or a large black spot on the sides of the body is present.

The Ginglymostomatidae are a cosmopolitan family of carpet sharks known as nurse sharks, containing four species in three genera. Common in shallow, tropical, and subtropical waters, these sharks are sluggish and docile bottom dwellers. They are the most abundant species of shark found in shallow coastal waters. Nurse sharks typically attack humans only if directly threatened.

Description

The largest species, called simply the nurse shark Ginglymostoma cirratum, may reach a length of 4.3 m; the tawny nurse shark Nebrius ferrugineus is somewhat smaller at 3.2 m, and the short-tail nurse shark Pseudoginglymostoma brevicaudatum is by far the smallest at just 75 cm in length. The first of the three species may reach a weight of 110 kg. Yellowish to dark brown in colour, nurse sharks have muscular pectoral fins, two spineless dorsal fins (the second of which is smaller) in line with the pelvic and anal fins, and a tail exceeding one quarter the shark’s body length.

The mouth of nurse sharks is most distinctive; it is far ahead of the eyes and before the snout (subterminal), an indication of the bottom-dwelling (benthic) nature of these sharks. Also present on the lower jaw are two fleshy barbels, chemosensory organs that help the nurse sharks find prey hidden in the sediments. Behind each eye is a very small, circular opening called a spiracle, part of the shark’s respiratory system. The serrated teeth are fan-shaped and independent; like other sharks, the teeth are continually replaced throughout the animal’s life.

Habits

Nurse sharks are nocturnal animals, spending the day in large inactive groups of up to 40 individuals. Hidden under submerged ledges or in crevices within the reef, the nurse sharks seem to prefer specific haunts and return to them every day. By night, the sharks are largely solitary; they spend most of their time searching through the bottom sediments in search of food. Their diet consists primarily of crustaceans, molluscs, tunicates, and other fish, particularly stingrays.

Nurse sharks are thought to take advantage of dormant fish, which would otherwise be too fast for the sharks to catch; although their small mouths limit the size of prey items, the sharks’ large throat cavities are used as a sort of bellows valve. In this way, nurse sharks are able to suck in their prey. Nurse sharks are also known to graze algae and coral.

Reproduction

The mating season runs from late June to the end of July. All nurse sharks are aplacental viviparous, meaning the eggs develop and hatch within the body of the female, where the hatchlings develop further until live birth occurs. The gestation period is six months, with a typical litter of 30–40 pups. The mating cycle is biennial, as 18 months are needed for the female’s ovaries to produce another batch of eggs. The young nurse sharks are born fully developed at about 30 cm long in Ginglymostoma cirratum. They possess a spotted coloration that fades with age.

Sand sharks are mackerel sharks of the family Odontaspididae. They are found worldwide in temperate and tropical waters. The family contains two species in a single extant genus (Odontaspis), as well as several extinct genera. The genus Carcharias was formerly included in the family.

The body tends to be brown with dark markings in the upper half. These markings disappear as they mature. Their needle-like teeth are highly adapted for impaling fish, their main prey. Their teeth are long, narrow, and very sharp with smooth edges, with one and on occasion two smaller cusplets on either side. Sand sharks have a large second dorsal fin.

Location and origins

The name sand shark comes from their tendency to migrate toward shoreline habitats, and they are often seen swimming around the ocean floor in the surf zone; at times, they come very close to shore. They are often found in warm or temperate waters throughout the world’s oceans, except the eastern Pacific. They also frequent the Mediterranean and Adriatic Seas at depths from 20 to 200 m and sometimes more.

Behavior

The sand shark has a unique hunting strategy. It is able to gulp air from above the surface and collect the air in its stomach. This enables it to become buoyant and approach its prey virtually motionless. During the day, the sand shark stays mostly inactive, but at night, it becomes active and resumes hunting activities. Its staple is small fish, but it eats crustaceans and squid, as well. It occasionally hunts in shivers (groups), and has even been known to attack full fishing nets.

Reproduction

Sand sharks only develop two embryos, one in each uterus. The largest and strongest embryos consume their siblings in the womb (intrauterine cannibalism) before each surviving pup is born. It has one of the lowest reproduction rates of all sharks and is susceptible to even minimal population pressure, so it is listed as vulnerable and is protected in much of its range.

Attacks on people

Sand sharks are not known to attack humans. If a person were to provoke a sand shark, it may retaliate defensively. Sand sharks are generally not aggressive, but harass divers who are spearfishing. In North America, wreck divers regularly visit the World War II shipwrecks to dive with the sharks that make the wrecks their home.

The Lamnidae are the family of mackerel sharks known as white sharks. They are large, fast-swimming predatory fish found in oceans worldwide, though they prefer environments with colder water. The name of the family is formed from the Greek word lamna, which means “fish of prey”, and was derived from the Greek legendary creature, the Lamia.

These sharks have pointed snouts, spindle-shaped bodies, and large gill openings. The first dorsal fin is large, high, stiff and angular or somewhat rounded. The second dorsal and anal fins are minute. The caudal peduncle has a couple of less distinct keels. The teeth are gigantic. The fifth gill opening is in front of the pectoral fin and spiracles are sometimes absent. They are powerful, heavily built sharks, sometimes weighing nearly twice as much as other sharks of comparable length from other families. Many sharks in the family are among the fastest-swimming fish, although the massive great white shark is slower due to its large size.

Carcharodon

The great white shark (Carcharodon carcharias), also known as the white shark, white pointer, or great white, is a large shark. It is closely related to the mako sharks, the porbeagle, and the salmon shark. It is a robustly built species with a grayish upperside and a white underside. The white shark is one of the largest living shark and fish species, though it is still smaller than the whale shark and basking shark. It has about 300 triangular, serrated teeth that are continuously replaced. Its massive, fatty liver can reach over a quarter of its body weight, providing buoyancy and storing energy. The species is partially warm-blooded, an adaptation that allows it to remain active in colder waters.

White sharks inhabit tropical and temperate ocean waters around the world and can be found both near coasts and in the open ocean. Populations are most concentrated at the Pacific and Atlantic sides of North America and in the waters of southern Africa and Oceania. They are a highly migratory species, traveling between the coast and the open ocean and even between continents. The white shark preys on marine mammals such as seals and dolphins, as well as squid and fish, including other sharks. It also scavenges whale carcasses. Though normally an apex predator, the species is sometimes preyed on by orcas. White sharks are generally solitary, but may gather in aggregations, particularly at feeding sites. They may communicate and establish dominance hierarchies with body language. The species reproduces with pups hatching from eggs inside the female before being born live. Juvenile white sharks typically inhabit shallower water and are limited to feeding on smaller prey.

The white shark has a fearsome reputation among the public. In reality, white sharks normally do not prey on humans, and the majority of bites are due to curiosity or possibly mistaken identity. Many attempts have been made to keep the species in captivity, but specimens either ended up dying or being released. White shark aggregations have attracted tourists who may view them from boats or from inside shark cages.

Isurus

Mako sharks are predatory mackerel sharks of the genus Isurus (meaning “equal tail”). They are largely pelagic, and are fast, predatory fish capable of swimming at speeds of up to 50 km/h. They occur at depths of 50–250 m. When hunting, they are capable of powerful leaps above the water surface. They feed primarily on bony fishes, sea turtles, other marine animals, and cephalopods. Both mako sharks are sexually dimorphic, with females being larger than males, and are large sharks. Both species of mako shark are classified as “Endangered” by the IUCN.

Reproduction is viviparous, with females producing litters of up to 18 pups measuring 70–120 cm at birth.

Lamna

Lamna is a genus of mackerel sharks in the family Lamnidae, containing two extant species: the porbeagle (Lamna nasus) of the North Atlantic and Southern Hemisphere, and the salmon shark (Lamna ditropis) of the North Pacific.

The total length of representatives of this genus ranges from 2 to 3.5 m, with a body mass of 25–31 kg. Males are somewhat smaller than females. The head is conical, and the mouth is large, with 25–31 rows of teeth. The eyes are large and positioned on the upper part of the head. There are five gill slits. The body is robust. One anal fin is present, along with one or two dorsal fins. The pectoral fins are broad. Coloration is bluish or brown on the back and sides, with a lighter underside marked by numerous dark spots.

Mackerel sharks inhabit generally shallow waters, down to a maximum depth of about 650 m, and may form small groups. They are capable of tolerating low temperatures, down to −15 to −18 °C. Their diet consists mainly of small to medium-sized bony fishes.

Sexual maturity in males occurs between 2 and 12 years of age, while females typically mature earlier. These sharks are ovoviviparous, with females giving birth to litters of 2–5 pups measuring 40–75 cm in length. Life expectancy is up to about 65 years.

Thresher sharks are large mackerel sharks of the family Alopiidae found in all temperate and tropical oceans of the world; the family contains three extant species, all within the genus Alopias.

Despite being active predatory fish, thresher sharks do not appear to be a threat to humans.

Although occasionally sighted in shallow, inshore waters, thresher sharks are primarily pelagic; they prefer the open ocean, characteristically preferring water 550 m and less. Common threshers tend to be more prevalent in coastal waters over continental shelves. Common thresher sharks are found along the continental shelves of North America and Asia of the North Pacific, but are rare in the Central and Western Pacific. In the warmer waters of the Central and Western Pacific, bigeye and pelagic thresher sharks are more common. A thresher shark was seen on the live video feed from one of the ROVs monitoring BP’s Macondo oil well blowout in the Gulf of Mexico. This is significantly deeper than the 500 m previously thought to be their limit. A bigeye has also been found in the western Mediterranean, and so distribution may be wider than previously believed, or environmental factors may be forcing sharks to search for new territories.

Anatomy and appearance

Named for their exceptionally long, thresher-like heterocercal tail or caudal fins (which can be as long as the total body length), thresher sharks are active predators; the tail is used as a weapon to stun prey. The thresher shark has a short head and a cone-shaped nose. The mouth is generally small, and the teeth range in size from small to large. By far the largest of the three species is the common thresher, Alopias vulpinus, which may reach a length of 6.1 m and a mass of over 500 kg. The bigeye thresher, Alopias superciliosus, is next in size, reaching a length of 4.9 m; at just 3 m, the pelagic thresher, Alopias pelagicus, is the smallest.

Thresher sharks are fairly slender, with small dorsal fins and large, recurved pectoral fins. With the exception of the bigeye thresher, these sharks have relatively small eyes positioned to the forward of the head. Coloration ranges from brownish, bluish or purplish gray dorsally with lighter shades ventrally. The three species can be roughly distinguished by the primary color of the dorsal surface of the body. Common threshers are dark green, bigeye threshers are brown and pelagic threshers are generally blue. Lighting conditions and water clarity can affect how any one shark appears to an observer, but the color test is generally supported when other features are examined.

Diet

The thresher shark mainly feeds on schooling pelagic fish such as bluefish, juvenile tuna and mackerel, which they are known to follow into shallow waters, as well as squid and cuttlefish. Crustaceans and occasionally seabirds are also eaten. The thresher shark stuns its prey by using its elongated tail as a whipping weapon.

Behavior

Thresher sharks are solitary creatures that keep to themselves. It is known that thresher populations of the Indian Ocean are separated by depth and space according to sex. Some species however do occasionally hunt in a group of two or three contrary to their solitary nature. All species are noted for their highly migratory or oceanodromous habits. When hunting schooling fish, thresher sharks are known to “whip” the water. The elongated tail is used to swat smaller fish, stunning them before feeding. Thresher sharks are one of the few shark species known to jump fully out of the water, using their elongated tail to propel them out of the water, making turns like dolphins; this behavior is called breaching.

Reproduction

No distinct breeding season is observed by thresher sharks. Fertilization and embryonic development occur internally; this ovoviviparous or live-bearing mode of reproduction results in a small litter (usually two to four) of large well-developed pups, up to 150 cm at birth in thintail threshers. The young fish exhaust their yolk sacs while still inside the mother, at which time they begin feasting on the mother’s unfertilized eggs; this is known as oophagy.

Thresher sharks are slow to mature; males reach sexual maturity between seven and thirteen years of age and females between eight and fourteen years in bigeye threshers. They may live for 20 years or more.

The bullhead sharks are members of the genus Heterodontus, the only members of the family Heterodontidae and only living members of the order Heterodontiformes. All are relatively small, with the largest species reaching just 1.65 m in maximum length. They are bottom feeders in tropical and subtropical waters.

The Heterodontiforms appear in the fossil record in the Early Jurassic. The oldest fossils of the modern genus date to the Late Jurassic. Despite the very ancient origins of this genus and its abundance in the fossil record, phylogenetic evidence indicates that all extant species in the genus arose from a single common ancestor that survived the Cretaceous-Paleogene extinction, with diversification into modern species only starting around the mid-Eocene.

Description

Bullhead sharks have tapered bodies, with most species reaching around 70–130 cm in length. Their bodies vary in colour, including shades of grey, brown, and red and pale colours, and are covered in a variety of patterns, including spots and stripes. They have blunt, proportionally large heads with relatively small mouths and large nostrils, with pronounced ridges above their eyes. They have two dorsal fins, both substantial in size, the first larger than the second, each of which has a rigid fin spine at the front, along with an anal fin. The tail fin is also large, with upper and lower lobes separated by a notch. Bullhead sharks have differentiated teeth, with cusped grasping teeth at the front of the mouth, and flattened teeth at the back of the mouth. Their egg cases have a spiral colarettes running along their length.

Ecology

Bullhead sharks live in coastal littoral environments, generally shallower than 100 m, and are usually primarily active at night. Bullhead sharks ingest prey via suction feeding. They feed on invertebrate prey, including both hard prey such as crustaceans and sea urchins, and soft bodied prey such as octopuses, as well as predating on fish. They use their flattened teeth at the back of the mouth to crush hard-shelled prey and fish. Juveniles generally take softer prey than adults. The sharp fin spines provide a deterrent to being consumed by predators.

Bullhead shark egg cases are shaped like an auger, with two spiral flanges. This allows the egg cases to become wedged in the crevices of rocky sea floors, where the eggs are protected from predators; however, some bullhead sharks deposit their eggs on sponges or seaweed. Hatchlings are considered large for sharks, reaching over 14 cm in length by the time they leave the egg case. Bullhead shark eggs typically hatch after 7 to 12 months, depending on the species. The female Japanese bullhead shark has been known to deposit their eggs in one location along with other females, called a “nest”. The egg case of the Mexican hornshark features a tendril and more rigid flanges, suggesting that egg case design of this species primarily involves anchoring with tendrils rather than wedging into crevices.

This is one of the largest families of sharks, with over 45 species distributed worldwide in warm and temperate coastal seas. Most species occur in continental and insular waters, from the shoreline and intertidal to the outermost shelf, often close to the bottom, with many in sandy, muddy and rocky inshore habitats, enclosed bays and near river-mouths. A few deepwater species range down continental slopes to great depths, possibly exceeding 2,000 m. Many are endemic with a very restricted distribution.

Houndsharks are small- to medium-sized sharks with two medium to large spineless dorsal fins, the base of the first dorsal fin positioned well ahead of the pelvic-fin bases, and an anal fin. They have horizontally oval eyes with nictitating eyelids. Nasoral grooves are absent, and the anterior nasal flaps are not barbel-like (except in Furgaleus). The mouth is long, angular or arched, and extends past the front of the eyes. Labial furrows range from moderate to very long. The caudal fin lacks a strong lower lobe and does not exhibit lateral undulations along its dorsal margin. Some genera (e.g., Mustelus) are difficult to distinguish without vertebral counts, and several species remain undescribed.

Some species are highly active and swim almost continuously, while others are capable of resting on the bottom; many swim close to the seabed. Activity patterns vary, with some species being primarily diurnal and others nocturnal.

Houndsharks are viviparous, either with or without a yolk-sac placenta, and produce litters ranging from 1–2 up to 52 pups. They feed mainly on benthic and midwater invertebrates and bony fishes; some species primarily consume crustaceans, others mainly fishes, and a few specialize on cephalopods. None are known to feed on birds or mammals.

The hammerhead sharks are a group of sharks that form the family Sphyrnidae, named for the unusual and distinctive form of their heads, which are flattened and laterally extended into a cephalofoil (a T-shape or “hammer”). The shark’s eyes are placed one on each end of this T-shaped structure, with their small mouths directly centered and underneath. Most hammerhead species are placed in the genus Sphyrna, while the winghead shark is placed in its own genus, Eusphyra. Many different—but not necessarily mutually exclusive—functions have been postulated for the cephalofoil, including sensory reception, manoeuvering, and prey manipulation. The cephalofoil gives the shark superior binocular vision and depth perception, as well as increased surface area for electrocreceptors.

Hammerheads are found worldwide, preferring life in warmer waters along coastlines and continental shelves. Unlike most sharks, some hammerhead species will congregate and swim in large schools during the day, becoming solitary hunters at night.

Hammerhead shark species vary in length and weight. The largest species, the great hammerhead, has an average length of 4 m and weight of 230 kg. The smallest species, the bonnethead shark, can reach 1.5 m in length and 10.8 kg in weight. One specimen caught off the Florida coast in 1906 weighed over 680 kg. They are usually light gray and have a greenish tint. Their bellies are white, which allows them to blend into the background when viewed from below and sneak up to their prey. Their heads have lateral projections that give them a hammer-like shape. While overall similar, this shape differs somewhat between species; examples are: a distinct T-shape in the great hammerhead, a rounded head with a central notch in the scalloped hammerhead, and an unnotched rounded head in the smooth hammerhead.

Hammerheads have disproportionately small mouths compared to other shark species. Some species are also known to form schools. In the evening, like most other sharks, they become solitary hunters. National Geographic explained that hammerheads can be found in warm, tropical waters, but during the summer, they begin a mass migration period in search of colder waters.

Cephalofoil

The hammer-like shape of the head may have evolved at least in part to enhance the animal’s vision. The positioning of the eyes, mounted on the sides of the shark’s distinctive hammer head, allows 360° of vision in the vertical plane, meaning the animals can see above and below them at all times. They also have an increased binocular vision and depth of visual field as a result of the cephalofoil. The shape of the head was previously thought to help the shark find food, aiding in close-quarters maneuverability, and allowing sharp turning movement without losing stability. The unusual structure of its vertebrae, though, has been found to be instrumental in making the turns correctly, more often than the shape of its head, though it would also shift and provide lift. From what is known about the winghead shark, the shape of the hammerhead apparently has to do with an evolved sensory function. Like all sharks, hammerheads have electroreceptory sensory pores called ampullae of Lorenzini. The pores on the shark’s head lead to sensory tubes, which detect electric fields generated by other living creatures. By distributing the receptors over a wider area, like a larger radio antenna, hammerheads can sweep for prey more effectively.

Reproduction

Reproduction occurs only once a year for hammerhead sharks, and usually occurs with the male shark biting the female shark violently until she agrees to mate with him. The hammerhead sharks exhibit a viviparous mode of reproduction with females giving birth to live young. Like other sharks, fertilization is internal, with the male transferring sperm to the female through one of two intromittent organs called claspers. The developing embryos are at first sustained by a yolk sac. When the supply of yolk is exhausted, the depleted yolk sac transforms into a structure analogous to a mammalian placenta (called a “yolk sac placenta” or “pseudoplacenta”), through which the mother delivers sustenance until birth. Once the baby sharks are born, they are not taken care of by the parents in any way. Usually, a litter consists of 12 to 15 pups, except for the great hammerhead, which gives birth to litters of 20 to 40 pups. These baby sharks huddle together and swim toward warmer water until they are old and large enough to survive on their own.

In 2007, the bonnethead shark was found to be capable of asexual reproduction via automictic parthenogenesis, in which a female’s ovum fuses with a polar body to form a zygote without the need for a male. This was the first shark known to do this.

Diet

Hammerhead sharks eat a large range of prey such as fish (including other sharks), squid, octopus, and crustaceans. Stingrays are a particular favorite, with the positioning of their (comparatively) smaller, crescent-shaped mouths underneath their T-shaped heads allowing for skilled skate, ray, and flounder hunting, among other seafloor-dwellers. These sharks will often be found swimming above the sand along the bottom of the ocean, stalking their prey. Their unique heads are further utilized as a tool (or weapon) if hunting rays and flatfishes; the shark uses its head to pin down and briefly stun the prey, and only eats once their quarry is clearly weakened and in shock. The great hammerhead, tending to be larger and more aggressive to its own kind than other hammerheads, occasionally engages in cannibalism, eating other hammerhead sharks, including mothers consuming their own young. In addition to the typical animal prey, bonnetheads have been found to feed on seagrass, which sometimes makes up as much as half their stomach contents. They may swallow it unintentionally, but they are able to partially digest it. At the time of discovery, this was the only known case of a potentially omnivorous species of shark (since then, whale sharks were also found to be omnivorous).

Relationship with humans

According to the International Shark Attack File, humans have been subjects of 17 documented, unprovoked attacks by hammerhead sharks within the genus Sphyrna since AD 1580. No human fatalities have been recorded. Most hammerhead shark species are too small to inflict serious damage to humans.

The great and the scalloped hammerheads are listed on the World Conservation Union’s (IUCN) 2008 Red List as endangered, whereas the smalleye hammerhead is listed as vulnerable. The status given to these sharks is as a result of overfishing and demand for their fins, an expensive delicacy.

Scyliorhinidae is a family of sharks, one of a few families whose members share the common name catsharks, belonging to the order Carcharhiniformes, the ground sharks. Although they are generally known as catsharks, some species can also be called dogfish due to previous naming. However, a dogfish may generally be distinguished from a catshark as catsharks lay eggs while dogfish have live young, as well as the fact that dogfish lack an anal fin. Like most bottom feeders, catsharks feed on benthic invertebrates and smaller fish. They are not harmful to humans. The family is paraphyletic, containing several distinct lineages that do not form a monophyletic group.

Anatomy and appearance

Scyliorhinidae catsharks may be distinguished by their elongated, cat-like eyes and two small dorsal fins set far back. Most species are fairly small, growing no longer than 80 cm; a few, such as the nursehound (Scyliorhinus stellaris) can reach 1.6 m in length. Most of the species have a patterned appearance, ranging from stripes to patches to spots.

The sonic hedgehog dentition expression is first found as a bilateral symmetrical pattern and is found in certain areas of the embryonic jaw. Sonic hedgehog (a secreted protein that, in humans, is encoded by the SHH gene) is involved in the growth and patterning of different organs. Every 18–38 days the teeth are replaced as is a common characteristic of the developmental process of sharks.

The “swell sharks” of the genus Cephaloscyllium have the curious ability to fill their stomachs with water or air when threatened, increasing their girth by a factor of one to three.

Some catsharks, such as the chain catshark (Scyliorhinus retifer) are biofluorescent.

Distribution

Scyliorhinidae catsharks are found around seabeds in temperate and tropical seas worldwide, ranging from very shallow intertidal waters to depths of 2,000 m or more. They are usually restricted to small ranges. Juvenile and adult chain catshark (Scyliorhinus retifer) live on the soft or rocky bottom of the Atlantic from Massachusetts to Nicaragua. Adults tend to live on the soft, sandy bottoms possibly due to their need of egg deposition sites.

Behaviour

Scyliorhinidae includes species that do not undergo long distance migrations because they are poor swimmers. Due to being nocturnal, some species sleep close together in crevices throughout the day and then go hunting at night. Some species such as the small-spotted catshark (Scyliorhinus canicula), are sexually monomorphic and exhibit habitat segregation, where males and females live in separate areas; males tend to live in open seabeds, while females tend to live in caves. Some species of catsharks may deposit egg cases in structured habitats, which may also act as nurseries for the newly hatched sharks.

Reproduction

Scyliorhinidae includes many species of catsharks, that like the chain catshark (Scyliorhinus retifer), are oviparous and lay eggs in tough egg cases with curly tendrils at each end, known as “mermaid’s purses”, for protection, onto the seabed. Almost a year is needed for a catshark to hatch from the egg. Instead of laying the eggs and letting them sit for a year, some species of catsharks hold onto the eggs until a few months before the shark hatches. Some catsharks exhibit ovoviviparity, aplacental viviparous, by holding onto the embryos until they are completely developed and then give live birth. Some species of catsharks mate by biting and holding the female’s pectoral fins and wrestle her into a mating position.