Scyliorhinidae

Diversity

The family Scyliorhinidae is the largest shark family, with at least 15 genera and over 100 species. Their common name, catsharks, likely derives from their elongated, cat-like eyes, although their scientific name is based on the Greek words, “Scylla,” meaning “a shark,” and “rhinos,” meaning “nose.” Some members of Scyliorhinidae are also commonly known as dogfish. Members of this family tend to be small, usually less than 1 m long, and are harmless to humans. Most catsharks live in seas above the upper continental slope, a location that makes it difficult to observe these sharks and collect specimens. Therefore, much information about catsharks remains to be discovered.

Geographic Range

Catsharks occur in warmer seas around the globe. Many species of catshark are endemic to certain locations, for example seas off Australia or South Africa. Some, such as Apristurus laurussoni , venture into the Arctic Ocean, but most live between 40 degrees north and south latitudes. Catsharks, along with other members of the order Carcharhiniformes , make up the majority of sharks in many tropical and warm temperate seas.

• Biogeographic Regions
• nearctic nearctic
  • native native
• palearctic palearctic
  • native native
• oriental oriental
  • native native
• ethiopian ethiopian
  • native native
• neotropical neotropical
  • native native
• australian australian
  • native native
• oceanic islands oceanic islands
  • native native
• arctic ocean arctic ocean
  • native native
• indian ocean
  • native native
• atlantic ocean atlantic ocean
  • native native
• pacific ocean pacific ocean
  • native native
• mediterranean sea
  • native native

• Other Geographic Terms
• cosmopolitan cosmopolitan

Habitat

Catsharks most frequently live near the bottom, ranging from shallow intertidal zones to depths of more than 2000 m. Many occur along continental and insular slopes, and this deepwater habitat makes many catsharks difficult to observe and collect. Near Australia, catsharks have been observed inhabiting ledges and caves, seagrass or kelp beds, coastal reefs, and both sandy and rocky bottoms. Some catsharks (members of Parmaturus and probably Cephalurus ) are able to live in benthic habitats tolerable to few other fishes: enlarged branchial (gill) regions enable them to survive very low oxygen levels, high temperatures, and high salinity.

• Habitat Regions
• temperate temperate
• tropical tropical
• saltwater or marine saltwater or marine

• Aquatic Biomes
• benthic benthic
• coastal coastal

• Other Habitat Features
• intertidal or littoral intertidal or littoral

Physical Description

Catsharks (family Scyliorhinidae) are small sharks. Most are less than 80 cm long, but some, i.e. Scyliorhinus stellaris , attain a length of at least 1.6 m. The bodies of catsharks are fusiform (cylindrical, tapering at the ends) to slightly depressed. The snout may be short or elongated, and sometimes forms a bell shape when seen from above or below. This family has elongated, catlike eyes situated high on the sides of the head. They possess rudimentary nictitating lower eyelids. These membranes, essentially a third eyelid, can cover the exposed portion of the eye, since, as in all sharks, the upper and lower eyelids of catsharks cannot completely cover the eyeball. Catsharks have moderately large spiracles, or respiratory openings, and five pairs of gill slits. Teeth are small and multicuspid, with 40 to 111 rows of teeth in each jaw. In some cases the rear teeth are comblike. In various species of catshark from at least seven genera, females and adult males have different tooth shape. This is called sexual heterodonty, and it occurs most strongly in smaller species of catshark. Adult males in these cases tend to have much larger teeth than females or immature males, and larger, higher, and differently-shaped cusps. One researcher suggests that the modifications of the teeth in adult males may contribute to their ability to grasp a female during courtship. In all catsharks, the base of the first dorsal fin is opposite or behind the base of the first pelvic fin. There are two dorsal fins, both without spines. Anal and caudal fins are also present. Catsharks may be a plain color ranging from grayish to dark brown, or may have color patterns of blotches, spots, or saddles. Like other sharks, catsharks are covered with placoid scales. All sharks have a valvular intestine, and in catsharks the valve has a conicospiral shape, with between five and 21 turns.

• Other Physical Features
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike
• sexes shaped differently

Development

Catsharks begin life inside spindle-shaped egg cases known to beachcombers as “mermaids’ purses.” In most cases the embryo develops, inside its egg case, within the mother’s uterus until it is almost ready to hatch. Then the mother deposits the egg on the sea bottom or other surface. Long, curling tendrils extend from each of the four corners of an egg case to help secure it to the substrate. Slits in the tendrils allow water to flow through the egg case. The young catshark continues to develop until it hatches, looking like a miniature adult. Hatching time ranges from less than a month to more than a year. There is no larval stage. In about 10% of catsharks, from the genera Galeus , Halaelurus , and Cephalurus , the embryo completes its entire development inside the mother and is born directly into the sea. Male carcharhinids, including catsharks, have reached sexual maturity when their clasper (male organ for internally fertilizing a female) cartilages have become calcified and rigid, rather than small, soft, and flexible as in immature males. The presence of large ovaries with follicles marks adulthood in females.

Reproduction

Only a few species of elasmobranch (subclass including all sharks and rays) fishes have been observed during courtship and mating. However, sharks have a system that involves internal fertilization, and elasmobranch fishes have relatively complex endocrine (hormonal) systems. Based on knowledge of other vertebrates with similar systems, it is likely that females signal to males through chemical or behavioral cues to indicate when their hormonal state is appropriate for mating. Some female sharks have been observed behaving in specific ways prior to mating, followed by passive behavior during copulation that permits the biting and grasping behavior of the male. It is likely that some catsharks participate in this pattern. Mating in some sharks lasts for 15 to 20 minutes, but specific information regarding length of copulation in catsharks was not found. In order to inseminate the female, the male inserts into her one of his two claspers, organs that are grooved extensions of the rear bases of the pelvic fins. In most catsharks the clasper groove is covered by soft tissue, forming a tunnel down which semen travels into the female. In at least one species of catshark, Scyliorhinus canicula , the female is able to store sperm for delayed insemination.

At least 90% of known catsharks are oviparous, meaning they lay eggs. Many of these catsharks produce eggs all year, with seasonal increases in the number of females laying eggs. Most catsharks have a system called single oviparity, in which an egg develops inside each oviduct and is deposited outside the female, remaining attached to the substrate until it hatches. Hatching time may be less than a month or nearly a year. At least one species of Galeus and four species of Halaelurus have multiple oviparity. In this case several eggs develop in each oviduct, and hatching time tends to be shorter (23 to 36 days in Halaelurus lineatus ). Catshark egg cases, made from a keratin-like collagen, tend to be rectangular in shape, with rounded sides and narrow ends. Tendrils from each corner help anchor the egg to the substrate. A special gland in the female, unique to elasmobranchs and known as the oviducal, nidamental, or shell gland, produces the egg case.

Although egg cases provide a tough protective shield, developing embryos inside them are still vulnerable to predation. Some sharks have evolved a system called ovoviviparity or aplacental viviparity to protect their young until a later stage of development. It is estimated that oviparity evolved into viviparity at least 18 times within Chondrichthyes (class that includes sharks). Ovoviviparous sharks give birth to live young, and a few members of Scyliorhinidae (from the genera Galeus , Halaelurus , and Cephalurus ) fall into this category. In this system, the egg is retained inside the uterus, and the young catshark develops there until it is born directly into the sea and can swim away like a miniature adult. Only one young at a time develops within the uterus. Some ovoviviparous sharks secrete a uterine fluid that supplements the nutrition the developing young receives from the egg. No information was found to verify whether or not ovoviviparous catsharks share this characteristic.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• year-round breeding year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • internal internal
• ovoviviparous ovoviviparous
• oviparous oviparous

No parental care has been observed in catsharks. Female catsharks contribute extensively to the survival of offspring by protecting them internally during development and even producing secretions that provide nutrition.

• Parental Investment
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female

Lifespan/Longevity

No specific information was found regarding lifespan in Scyliorhinidae. Sharks in general, however, tend to mature slowly and be long-lived.

Behavior

Catsharks are relatively slow-moving and non-migratory. Observers have noted that some catsharks in Asymbolus and Cephaloscyllium are nocturnal. Others, like sawtail sharks , appear to group according to sex. One genus within Scyliorhinidae, swell sharks , can swallow air or water to inflate immensely. There is no evidence that any catsharks display territoriality, which may be due to the fact that most food sources for sharks are difficult to defend.

• Key Behaviors
• natatorial natatorial
• diurnal diurnal
• nocturnal nocturnal
• motile motile
• sedentary sedentary
• solitary solitary

Communication and Perception

Catsharks, like other elasmobranchs , have a high sensitivity to electric fields created by the movement of water, of other fishes, and even the movement of the earth. In experiments Scyliorhinus canicula , for example, demonstrated sensitivity to extremely low voltage gradients. In principle, sharks can use this sense to navigate according to the earth’s magnetic fields, and to detect prey. The special receptors used for this mode of perception are called the ampullae of Lorenzini, distributed around the shark’s head. Catsharks, like all other fishes, sense their environment hydrodynamically through the lateral line, a series of pores connecting a complex internal canal system with the outside water. They also possess, like other elasmobranchs , pit organs that lie between the bases of scales and add to information provided by the lateral line. Members of the family Scyliorhinidae are raptorial predators, and therefore have keen senses of hearing, taste, and smell that help them sense and find food sources. Experiments on species of Scyliorhinidae suggest that the pineal gland in the brain may serve as a keen light sensor that cues the fish’s behavior to periodic changes in light.

• Communication Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical
• electric electric

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical
• electric electric
• magnetic magnetic

Food Habits

Small fish and invertebrates make up the diet of most catsharks. Some swellsharks, for example Cephaloscyllium ventriosum ( see image ), are sluggish bottom feeders that prey on dead or sleeping fish or crustaceans. Others have more active tactics to capture prey. For example, pyjama sharks , ( see image ) hide among squid eggs; they wait for the parent squid to become accustomed to a shark among its eggs, then devour the squid when it returns.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore
  • molluscivore molluscivore
  • scavenger scavenger

Predation

The most obvious anti-predator tactic among catsharks is that of the swell sharks , who are able to expand themselves enormously by swallowing air or water. All sharks are home to various parasites, especially in the skin, digestive system, and gills. Catsharks fall victim to predators even inside their tough, leathery egg cases, which are eaten by a variety of organisms from snails to possibly whales. Researchers have observed holes made by boring organisms in the egg cases of various species, including Cephaloscyllium ventriosum .

Ecosystem Roles

Catsharks occur around the globe in warm temperate seas, and therefore are a consistent predator on populations of squid, crustaceans, cephalopods, and small fishes. Catsharks, especially smaller specimens, provide food for other families of sharks and other large fishes.

Economic Importance for Humans: Positive

Some catsharks, for example Scyliorhinus in European seas, are important for fisheries. Deepwater species like some members of Apristurus have oil-rich livers but are not currently considered of commercial value. In general, humans capture and eat sharks around the world, but no significant commercial use was described for catsharks in particular. Some of the larger catsharks, like Scyliorhinus stellaris , are considered sport fish. Other species, like Scyliorhinus canicula , have been used for dissection in British educational institutions.

• Positive Impacts
• food food

Economic Importance for Humans: Negative

Catsharks are harmless to humans. One species, Cephaloscyllium laticeps , apparently can be a nuisance to lobster fishermen in parts of Australia when it enters lobster traps.

Conservation Status

Sharks in general are vulnerable to overfishing. They grow and mature slowly, and the size of the adult population closely determines the number of young produced, due to their “slow” reproductive strategy of investing a great deal of energy in relatively few young over a lifetime. As of 2001, one species of catshark was listed as vulnerable (facing a high risk of extinction in the wild), and eight species of catshark were listed as near threatened (approaching vulnerable status). Twenty species were listed as data deficient, meaning that not enough information has been collected to assess whether or not the species is threatened. These species may be threatened, however, especially if their geographic range is limited and few specimens have been found for data collection.

Other Comments

The earliest known fossils of catsharks date from the Upper Jurassic of Germany. Scyliorhinidae is the oldest group within the order Carcharhiniformes.

Additional Links

Encyclopedia of Life

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Monica Weinheimer (author), Animal Diversity Web.

References

Bleckmann, H., M. Hofmann. 1999. Special Senses. Pp. 300-328 in Sharks, Skates, and Rays . Baltimore, MD: The Johns Hopkins University Press.

Caira, J., C. Healy. 2004. Elasmobranchs as Hosts of Metazoan Parasites. Pp. `523-552 in Biology of Sharks and Their Relatives . Boca Raton, FL: CRC Press.

Compagno, L. 1988. Sharks of the Order Carcharhiniformes . Princeton, NJ: Princeton University Press.

Compagno, L. 1999. Systematics and Body Form. Pp. 1-19 in Sharks, Skates, and Rays . Baltimore, MD: The Johns Hopkins University Press.

Cox, D., T. Koob. 1993. Predation on elasmobranch eggs. Pp. 117-126 in The Reproduction and Development of Sharks, Skates, Rays, and Ratfishes . Dordrecht, The Netherlands: Kluwer Academic Publishers.

Froese, R., D. Pauly. 2004. "FishBase" (On-line). FishBase World Wide Web electronic publication. Accessed August 23, 2004 at http://www.fishbase.org/ .

Hamlett, W., T. Koob. 1999. Female Reproductive System. Pp. 398-443 in Sharks, Skates, and Rays . Baltimore, MD: The Johns Hopkins University Press.

Hamlett, W. 1999. Male Reproductive System. Pp. 444-470 in Sharks, Skates, and Rays . Baltimore, MD: The Johns Hopkins University Press.

Heithaus, M. 2004. Predator-Prey Interactions. Pp. 487-522 in Biology of Sharks and Their Relatives . Boca Raton, FL: CRC Press.

Helfman, G., B. Collete, D. Facey. 1997. The Diversity of Fishes . Malden, MA: Blackwell.

Last, P., J. Stevens. 1994. Sharks and Rays of Australia . Australia: CSIRO.

Last, P., J. Stevens. 1998. Sharks, Rays, and Chimaeras. Pp. 60-69 in Encyclopedia of Fishes – second edition . San Diego, CA: Academic Press.

Liem, K., A. Summers. 1999. Muscular System: Gross Anatomy and Functional Morphology of Muscles. Pp. 93-114 in Sharks, Skates, and Rays . Baltimore, MD: The Johns Hopkins University Press.

Moyle, P., J. Cech. 2004. Fishes: An introduction to ichthyology – fifth edition . Upper Saddle River, NJ: Prentice-Hall, Inc..

Musick, J., M. Harbin, L. Compagno. 2004. Historical Zoogeography of the Selachii. Pp. 33-78 in Biology of Sharks and Their Relatives . Boca Raton, FL: CRC Press.

Nelson, J. 1994. Fishes of the World – third edition . New York, NY: John Wiley and Sons.

Pratt, H. 1993. The storage of spermatozoa in the oviducal glands of western North Atlantic sharks. Pp. 139-149 in The Reproduction and Development of Sharks, Skates, Rays, and Ratfishes . Dordrecht, The Netherlands: Kluwer Academic Publishers.

The World Conservation Union, 2003. "IUCN 2003" (On-line). 2003 IUCN Red List of Threatened Species. Accessed August 23, 2004 at http://www.redlist.org/ .

Wheeler, A. 1975. Fishes of the World, an Illustrated Dictionary . New York, NY: Macmillan.

Wourms, J., L. Demski. 1993. The reproduction and development of sharks, skates, rays, and ratfishes: introduction, history, overview, and future prospects. Pp. 1-19 in The Reproduction and Development of Sharks, Skates, Rays, and Ratfishes . Dordrecht, The Netherlands: Kluwer Academic Publishers.