Some aquatic animals are sea turtles, jellyfish, clownfish and blue whales. These animals, which spend the majority of their lives in the water, represent several animal classes such as reptiles, invertebrates, fish and mammals respectively.
The types of aquatic animals in a given location depend on the water habitat. For instance, clownfish live in the saltwater of the Indian Ocean, Pacific Ocean and Red Sea. Another saltwater fish, the red lionfish, is native to Indo-Pacific waters, but has spread invasively throughout the Atlantic Ocean. The long-horned cowfish, a brightly colored green, yellow and blue species, also lives in the Indo-Pacific.
There are also many aquatic invertebrate animals such as the Japanese sea nettle from the Pacific Ocean and the moon jelly from the Atlantic, Pacific and Indian Oceans. These boneless animals also lack the organs such as a brain and a heart found in most animal types. Instead, they often have tentacles and are made almost entirely of water.
Many reptile species are also considered aquatic, such as the saltwater-loving sea turtles of which there are seven species still alive. They naturally inhabit tropical waters and can grow up to 2,000 pounds. They are also one of the oldest aquatic species at 110 million years in existence. The largest aquatic animal and the largest animal ever to live on Earth is the blue whale, a mammal that grows up to 100 feet long and weighs in at 200 tons or 400,000 pounds.