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An aquatic animal is an animal, either vertebrate or invertebrate, which lives in water for most or all of its life. Some examples of invertebrates are coelenterates. This phylum consists of jellyfish, anemones, corals, and hydras. Another type of invertebrate aquatic animal is the annelids which are segmented worms. There are three different classes they are polychaetes, oligochaetes, and hirudinea. It may breathe air or extract its oxygen from that dissolved in water through specialised organs called gills, or directly through its skin. Natural environments and the animals that live in them can be categorized as aquatic (water) or terrestrial (land). Animals that move readily from water to land and vice versa are referred to as amphibians. When animals live in water, they have special adaptations to help them survive in an aquatic habitat. The more time the animal spends in the water the quicker they adapt to their new habitat. There are numerous ways that an aquatic animal can adapt to their habitat. The term aquatic can in theory be applied to animals that live in either freshwater (freshwater animals) or saltwater (seawater animals). However, the adjective marine is most commonly used for animals that live in saltwater, i.e. in oceans, seas, etc. Invasive aquatic animals require a water habitat, but do not necessarily have to live entirely in water. Aquatic animals (especially freshwater animals) are often of special concern to conservationists because of the fragility of their environments. Aquatic animals are subject to pressure from overfishing, destructive fishing, marine pollution and climate change. -------------------------------------------------
Air breathing aquatic animals
In addition to water breathing animals, e.g., fishes, mollusks etc., the term "aquatic animal" can be applied to air-breathing aquatic or sea mammals such...