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The thresher sharks have an extreme example of this tail in which the upper lobe has evolved into a weapon for stunning prey. Bottom-dwelling sharks such as catsharks and carpet sharks have tails with long upper lobes and virtually no lower lobe. The upper lobe is held at a very low angle, which sacrifices speed for maneuverability.
Many sharks can contract and dilate their pupils, like humans, something no teleost fish can do. Sharks have eyelids, but they do not blink because the surrounding water cleans their eyes. To protect their eyes some species have nictitating membranes. This membrane covers the eyes while hunting and when the shark is being attacked.
The broadnose sevengill shark (Notorynchus cepedianus) is the only extant member of the genus Notorynchus, in the family Hexanchidae.It is recognizable because of its seven gill slits, while most shark species have five gill slits, with the exception of the members of the order Hexanchiformes and the sixgill sawshark.
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Blacknose sharks are preyed upon by larger sharks, [7] and captives have been observed to perform an apparent threat display towards encroaching divers or newly introduced members of their species. The display consists of the shark hunching its back, lowering its pectoral fins, gaping its jaws, and swimming with an exaggerated side-to-side motion.
The reality is that humans are a bigger threat to sharks than they are to us. Sharks are apex predators that keep biodiversity balanced by maintaining the species below them in the food chain.
"We have to think about it in terms of the food web that's out in the ocean: Ultimately, at the very top of that cycle of life are the sharks and if we removed the sharks, smaller fish species ...
The bluntnose sixgill shark (Hexanchus griseus), often simply called the cow shark, is the largest hexanchoid shark, growing to 18 ft (5.5 m) in length. [2] It is found in tropical and temperate waters worldwide and its diet is widely varied by region.