Facts At Your Fingertips: The living world – Living in water
Creatures that live in oceans or rivers are specially adapted to move, breathe, and feed in water.
The oceans contain a wide variety of animal life, from tiny plankton to the gigantic blue whale.
Breathing under water
Fish, such as this stingray, and many other sea creatures breathe the oxygen dissolved in water using organs called gills.
Some small creatures absorb oxygen through their skin without using gills.
Water flows in through the fish’s mouth and over the gills, which absorb oxygen from the water
Hold your breath
Sea-dwelling reptiles, such as turtles, and mammals, such as whales, do not have gills. They have to come to the surface to breathe.
Killer whales breathe through blowholes at the top of their heads. They can dive and hold their breath for up to 20 minutes.
Jet- propelled
Some invertebrates, such as an octopus, move through the water using jet propulsion.
They suck water into their bodies and force it out behind them in a strong jet that pushes them forward.
Big creatures
Because the weight of their bodies is supported by the water, animals in the oceans can grow to enormous sizes.
The biggest of them all, the blue whale, can grow to 100 ft (30 m) long and weigh over 200 tons (180 metric tons).