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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 daggernose shark (Isogomphodon oxyrhynchus) is a little-known species of requiem shark, in the family Carcharhinidae, and the only extant member of its genus.It inhabits shallow tropical waters off northeastern South America, from Trinidad to northern Brazil, favoring muddy habitats such as mangroves, estuaries, and river mouths, though it is intolerant of fresh water.
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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.
It is typically found at depths of 90–430 m (300–1,410 ft), though at night it may move towards the surface or into shallower water. The bignose shark is plain-colored and grows to at least 2.7–2.8 m (8.9–9.2 ft) in length.
"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 ...
With his hand close to razor sharp teeth, shark expert Neil Harvey attempts tonic immobility in a large reef shark. Tonic can be induced by turning a shark upside down, but that's not the only way.