Portal:Sharks

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Sharks are a group of elasmobranch cartilaginous fishes characterized by a ribless endoskeleton, dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to the head. Modern sharks are classified within the division Selachii^{[page needed]} and are the sister group to the Batomorphi (rays and skates). Some sources extend the term "shark" as an informal category including extinct members of Chondrichthyes (cartilaginous fish) with a shark-like morphology, such as hybodonts. Shark-like chondrichthyans such as Cladoselache and Doliodus first appeared in the Devonian Period (419–359 million years), though some fossilized chondrichthyan-like scales are as old as the Late Ordovician (458–444 million years ago). The earliest confirmed modern sharks (Selachii) are known from the Early Jurassic around 200 million years ago, with the oldest known member being Agaleus, though records of true sharks may extend back as far as the Permian.

Sharks range in size from the small dwarf lanternshark (Etmopterus perryi), a deep sea species that is only 17 centimetres (6.7 in) in length, to the whale shark (Rhincodon typus), the largest fish in the world, which reaches approximately 12 metres (40 ft) in length. They are found in all seas and are common to depths up to 2,000 metres (6,600 ft). They generally do not live in freshwater, although there are a few known exceptions, such as the bull shark and the river sharks, which can be found in both seawater and freshwater, and the Ganges shark, which lives only in freshwater. Sharks have a covering of placoid scales (denticles) that protects the skin from damage and parasites in addition to improving their fluid dynamics. They have numerous sets of replaceable teeth.

Several shark species are apex predators, which are organisms that are at the top of their food chain with select examples including the bull shark, tiger shark, great white shark, mako sharks, thresher sharks and hammerhead sharks. Some sharks are filter-feeding planktivores, such as the whale shark and basking shark, which are among the largest fish ever lived. (Full article...)

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The tawny nurse shark, Nebrius ferrugineus, is a species of nurse shark, family Ginglymostomatidae, and the only extant member of the genus Nebrius. It is found widely along coastlines in the Indian and Pacific Oceans, preferring reefs, sandy flats, and seagrass beds from very shallow water to a depth of 70 m (230 ft). With a cylindrical body and a broad, flattened head, the tawny nurse shark is quite similar in appearance to the nurse shark (Ginglymostoma cirratum) of the Americas, from which it can be distinguished by its pointed-tipped dorsal fins and narrow, sickle-shaped pectoral fins. The maximum recorded length is 3.2 m (10.5 ft).

Nocturnal animals, tawny nurse sharks tend to spend the day resting in piles of two dozen or more individuals inside caves or under ledges. At night, they are active-swimming predators that use a powerful suction force to extract prey from inside holes and crevices. The diet of the tawny nurse shark consists mainly of octopus, though they also take other invertebrates, small bony fishes, and rarely sea snakes. This species is ovoviviparous, meaning the embryos hatch from egg capsules inside the mother. It is the only carpet shark in which the embryos are oophagous, feeding on eggs produced by the mother while inside the uterus. The litter size may be as small as one or two, based on the large size of near-term embryos.

Compared to the nurse shark, the tawny nurse shark has a more placid disposition and will often allow divers to touch and play with it. However, it should be accorded respect due to its powerful jaws and sharp teeth. This species is caught by commercial fisheries across most of its range for meat, fins, liver oil, leather, and fishmeal. It is also esteemed as a game fish off Queensland, Australia, and is known for its habit of spitting water in the faces of its captors. The World Conservation Union has assessed this species as Vulnerable.

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... that Hixxy and Sharkey created a schism in the UK rave music scene in 1995?
... that a shark cost a competitor a silver medal in the spearfishing event at the 2014 Micronesian Games?
... that the parasitic copepod Driocephalus cerebrinoxius burrows into the brains of sharks through their noses?

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Credit: Terry Goss

The great white shark is an exceptionally large lamniform shark found in coastal surface waters in all major oceans.

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... that male Arabian carpetsharks competing for a mate have been known to bite the claspers of their rivals?
... that the porbeagle has been known to "play" with kelp fronds, pieces of wood, and fishing floats?
... that the blind shark and the bluegrey carpetshark close their eyes when taken out of the water?
... that male Arabian carpetsharks competing for a mate have been known to bite the claspers of their rivals?
... that the whitefin, Cook's, Australian reticulate, spotted, leopard-spotted, painted, flagtail, speckled, saddled, and narrowbar swellsharks were all scientifically described in 2008, more than doubling the number of species in the genus Cephaloscyllium?

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General images

The following are images from various shark-related articles on Wikipedia.

Image 1Placoid Scale (from Shark anatomy)
Image 2Postural elements of the agonistic display of the Gray Reef Shark (from Shark agonistic display)
Image 3The whale shark, the world's largest fish, is classified as Endangered.

Binding legislation and harvest management strategies... are urgently needed to address the disproportionate impact of fisheries on cartilaginous fishes.

– IUCN global study 2010

(from List of threatened sharks)
Image 4Sharksucker (Echeneis naucrates) (from Shark agonistic display)
Image 5Great white shark cages at Isla Guadalupe, Mexico (from Shark cage diving)
Image 6Great white shark at Isla Guadalupe, Mexico, August 2006. Animal estimated at 11–12 feet (3.3 to 3.6 m) in length, age unknown. (from Shark tourism)
Image 7A 14-foot (4.3 m), 1,200-pound (540 kg) tiger shark caught in Kāne'ohe Bay, Oahu, in 1966
Image 8Distribution of highly sensitive ampullae of Lorenzini across the shark's head and rostrum. (from Shark agonistic display)
Image 9Shark Anatomy (50693674756) (from Shark anatomy)
Image 10White shark cage diving near Gansbaai in South Africa (2015) (from Shark cage diving)
Image 11A ventral dissection of a pregnant female dogshark exposing its internal gill slits and internal spiracles. (from Shark anatomy)
Image 12Sharks swimming outside shark-proof cage with people inside (from Shark cage diving)
Image 13This grey reef shark demonstrates countershading, with its darker dorsal surface and lighter ventral surface. (from Shark anatomy)
Image 14Depiction of shark anatomy including eggs, pups, and the liver (from Shark anatomy)
Image 15In a milestone decision in 2013, CITES prohibited international trade in the fins of the scalloped hammerhead (pictured) and four other shark species. (from List of threatened sharks)
Image 16Postural configuration of a Gray Reef Shark as it displays agonistic behaviour, in a sculpture (from Shark agonistic display)
Image 17Dorsal fin diagram with landmarks labeled. (from Shark anatomy)
Image 18Branchiostoma lanceolatum (from Shark anatomy)
Image 19A dissected view of the unique four-chambered heart of the sharkChambers: Sinus Venosus, Atrium, Ventricle, Conus Ateriosus (from Shark anatomy)
Image 20The gill slits of a whale shark flaring as it expels water from its pharyngeal cavity. (from Shark anatomy)
Image 21Anti-cull protesters on Perth's Cottesloe Beach in Western Australia in 2014 (from Shark culling)
Image 22Lateral and cross section view of shark's red and white locomotor muscles (from Shark anatomy)
Image 23Shark cage diving (from Shark tourism)
Image 24Clear agonistic behaviour observed in Great White Shark (from Shark agonistic display)
Image 25The major features of sharks (from Shark anatomy)
Image 26A sign at Pyramid Rock Beach in Hawaii warning about a shark sighting, 2015 (from Shark tourism)

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Topics

Shark · Outline of sharks

Shark orders

Carcharhiniformes (groundsharks) · Cladoselachiformes (extinct) · Eugeneodontida (extinct) · Heterodontiformes (bullhead sharks) · Hexanchiformes (most primitive sharks) · Hybodontiformes (extinct) · Iniopterygia (extinct) · Lamniformes (mackerel sharks) · Orectolobiformes (carpet sharks and relatives) · Pristiophoriformes (sawsharks and relatives) · Squaliformes (gulper sharks, bramble sharks, lantern sharks, rough sharks, sleeper sharks, dogfish sharks and relatives) · Squatiniformes (angel sharks) · Symmoriida (extinct) · Xenacanthida (also known as Xenacantiformes, extinct)

Major species