It must distinguish between animals that can be exploited for breathing the oxygen dissolved in water and they need oxygen to breathe the air.
Aquatic animals are distributed throughout the zoological scale water being almost exclusively those of lower groups as well as sponges, polyps and echinoderms, large numbers of worms, most of all molluscs and brachiopods, and tunicates. Of arthropods that live in water, almost all crustaceans, arachnids and are rarely low number of insects that dwell therein.
Also abound among vertebrates in aquatic animals distinguished between those who live completely in the water breathing through gills like fish and all the larval forms of amphibians although the latter, in their adult forms (with pulmonary respiration) are sometimes the water com frogs and salamanders and other, land and the toad.
Other vertebrates breathe through lungs, but this is not an obstacle to have among them many aquatic species such as:
among the reptiles, many turtles, some snakes and crocodiles and alligators.
among birds, wading and large numbers of mosquitoes.
among mammals, cetaceans and pinnipeds, various rodents such as beaver, some carnivores such as otters and some elephants and a hippopotamus.
aquatic animals live in rivers, lakes and seas.
mammal aquatic animal is the dolphin, sea lions, manatees and whales, and the rest are oviparous, as the fish.
