An aquatic animal is an animal, either vertebrate or invertebrate, which lives in water for most or all of its life. Meaning they were born with or without a spine. 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.