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Why do snakes have slits for pupils?

Why do snakes have slits for pupils? Vertical pupils are an adaptation for ambush hunting. A 2010 study at sydney university found that of 127 Australian snake species, the ones that ambushed their prey by night had vertical pupils, while those that actively chased down prey in the day had round pupils. the constriction of round pupils helps distant prey stay in focus, but it also lets in less light. Vertical pupils improve vision across a wider range of light levels, and enable the animal to detect horizontal movement more effectively. it’s also possible that vertical pupils are more camouflaged, since they break up the round outline of the eye

DO ALL FISH AND SHELLFISH CONTAIN MERCURY?

Mercury levels in the oceans have tripled since the Industrial Revolution, thanks to mining and the burning of fossil fuels. All sea creatures absorb some of this heavy metal directly, and, once it’s in the body, there’s no way of getting rid of it. The amount of mercury in fish varies between species. Long-lived predators like tuna and swordfish tend to contain the most, because they also absorb mercury from their prey and they’ve had a long time to accumulate it. The lowest levels are found in short-lived species lower down the food chain, such as oysters and shrimp.

why do some fish have colourless blood?

Antarctic icefish have colourless blood with no red blood cells and no haemoglobin, the oxygen-carrying pigment. This probably comes down to a genetic mutation, and means their blood carries 90 per cent less oxygen than red blood. They survive partly because frigid Antarctic waters are oxygen-rich. Icefish also have enormous hearts that pump huge volumes of blood around their bodies, making sure they get enough oxygen. Antifreeze in their blood stops them from freezing (the salty Southern Ocean gets down to -2°C) but, as they are so well-adapted to the cold, their future in a warming world remains uncertain.