Hundreds of millions of years ago, the very, very distant ancestors of humans, and of all land animals with backbones and four limbs, had this ability to breathe in water, but it was lost after the first creatures to breathe air began to live on earth full time.
Today, humans can only breathe in water with special equipment or in fiction with unique underwater abilities, as in the case of Aquaman.
The comics explain how the half-human, half-Atlantean hybrid Aquaman , and all of his human-looking Atlantean cousins, can breathe in the depths of the ocean thanks to “gills” that are not visible, so the details remain for to the imagination of the reader or viewer. But how exactly do real-world creatures breathe in their watery environments?
There is a large amount of dissolved oxygen in most of the planet’s seas, lakes and rivers, although our air-breathing lungs simply cannot process it. But the inhabitants of the aquatic world have developed other methods to access the oxygen in the water.
Some animals, like jellyfish, absorb oxygen from water directly through their skin. A gastrovascular cavity within their bodies serves a dual purpose: digesting food and carrying oxygen and carbon dioxide.
In fact, the first forms of microbial life on Earth that used oxygen obtained it in the same way and that is, this form of respiration probably appeared about 2.8 billion years ago.
Curiosities
Respiration through the diffusion of oxygen over the surface of the body is also found in echinoderms , a group of marine animals that includes starfish, sea urchins, and sea cucumbers.
Starfish absorb oxygen as water flows through bumps on their skin called papules, and through grooves in other structures called tube legs. However, some types of shallow-water sea cucumbers have a different type of specialized adaptation for breathing: a respiratory “tree” structure located in the body cavity near the anus. As the cucumber’s rectal opening sucks water into your body, the respiratory tree draws in oxygen and expels carbon dioxide (yes, that’s just what you’re thinking: breathe through your butt).
In fish, gills have been shown to be a successful system for respiration, using a network of blood vessels to extract oxygen from flowing water and diffuse it through the gill membranes, according to the National Oceanic and Atmospheric Administration (NOAA). ).
In most fish, the gills follow this same path. However, gills aren’t exactly a one-size-fits-all instrument. Its structure can vary from one species to another to adapt to oxygen needs. The gills of a fast swimming tuna will vary a bit from those of a crocodile, for example. Well, active predators have different gills for their greater oxygen demand.
The shape of the gills can even vary between individuals of the same species, depending on the oxygen conditions in the water where they live. Studies have shown that fish can adapt their gill morphology when their watery habitat becomes contaminated. Over time, their gill filaments become more condensed to resist contaminants in the water.
