Portal:Sharks
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Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorpha (or Selachii) and are the sister group to the Batoidea (rays and kin). 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 oldest confirmed modern sharks (selachimorphs) are known from the Early Jurassic, about 200 million years ago, 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 shark, which can be found in both seawater and freshwater. Sharks have a covering of dermal denticles that protects their skin from damage and parasites in addition to improving their fluid dynamics. They have numerous sets of replaceable teeth.
Several species are apex predators, which are organisms that are at the top of their food chain. Select examples include the tiger shark, blue shark, great white shark, mako shark, thresher shark, and hammerhead shark. (Full article...)
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Young velvet bellies feed mainly on krill and small bony fish, transitioning to squid and shrimp as they grow larger. There is evidence that individuals also move into deeper water as they age. This species exhibits a number of adaptations to living in the deep sea, such as specialized T-cells and liver proteins for dealing with the higher concentrations of heavy metals found there. Velvet bellies often carry a heavy parasite load. It is ovoviviparous, giving birth to litters of 6–20 young every 2–3 years. This species has virtually no commercial value but large numbers are caught as bycatch in deepwater commercial fisheries. Although its population status has not been assessed, the heavy fishing pressure throughout its range and its slow reproductive rate are raising conservation concerns.
Did you know (auto-generated)
- ... that Timo Meier became the first player in San Jose Sharks franchise history to score five goals in one game when he was 25?
- ... that the ampullae of Lorenzini enable sharks to sense electric fields?
- ... that Hixxy and Sharkey created a schism in the UK rave music scene in 1995?
- ... that "the Hurricane Shark is real"?
- ... that since 2018, IKEA's stuffed toy shark Blåhaj has become a popular Internet meme and an icon of the online transgender community?
- ... that Alexis Sharkey's last Instagram post before her murder documented her travels to Tulum, Mexico?
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More Did you know? - show different entries
- ... that the Portuguese dogfish is the deepest-living shark known, found as far down as 3,675 m (2.284 mi)?
- ... that the single known specimen of the Irrawaddy river shark was generally dismissed as an abnormal bull shark until 2005?
- ... that the green lanternshark often preys on squid and octopus much larger than itself, which it may overwhelm by attacking in packs?
- ... that the barbeled houndshark is the only shark with a spherical placenta?
- ... that the cookiecutter shark may use the absence of bioluminescence to attract prey?
General images
- Image 1The gill slits of a whale shark flaring as it expels water from its pharyngeal cavity. (from Shark anatomy)
- Image 2Postural configuration of a Gray Reef Shark as it displays agonistic behaviour, in a sculpture (from Shark agonistic display)
- Image 3Dorsal fin diagram with landmarks labeled. (from Shark anatomy)
- Image 4Lateral and cross section view of shark's red and white locomotor muscles (from Shark anatomy)
- Image 5BranchiostomaLanceolatum PioM (from Shark anatomy)
- Image 7Great white shark cages at Isla Guadalupe, Mexico (from Shark cage diving)
- Image 8A sign at Pyramid Rock Beach in Hawaii warning about a shark sighting, 2015 (from Shark tourism)
- Image 9Sharks swimming outside shark-proof cage with people inside (from Shark cage diving)
- Image 11Sharksucker (Echeneis naucrates) (from Shark agonistic display)
- Image 12A dissected view of the unique four-chambered heart of the sharkChambers: Sinus Venosus, Atrium, Ventricle, Conus Ateriosus (from Shark anatomy)
- Image 13Shark cage diving (from Shark tourism)
- Image 14The 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
- Image 15This grey reef shark demonstrates countershading, with its darker dorsal surface and lighter ventral surface. (from Shark anatomy)
- Image 16Clear agonistic behaviour observed in Great White Shark (from Shark agonistic display)
- Image 17Distribution of highly sensitive ampullae of Lorenzini across the shark's head and rostrum. (from Shark agonistic display)
- Image 18A ventral dissection of a pregnant female dogshark exposing its internal gill slits and internal spiracles. (from Shark anatomy)
- Image 19Depiction of shark anatomy including eggs, pups, and the liver (from Shark anatomy)
- Image 20In 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 21Anti-cull protesters on Perth's Cottesloe Beach in Western Australia in 2014 (from Shark culling)
- Image 22Great 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 23The major features of sharks (from Shark anatomy)
- Image 24Placoid Scale (from Shark anatomy)
- Image 25Postural elements of the agonistic display of the Gray Reef Shark (from Shark agonistic display)
- Image 26Shark Anatomy (50693674756) (from Shark anatomy)
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