The world's largest fauna, in terms of body size, is the blue whale (Balaenoptera musculus). Blue whales are marine mammals and are considered the largest animals ever to have existed on Earth. They can reach lengths of up to 100 feet (30 meters) and weigh up to 200 tons. Blue whales primarily feed on small shrimp-like animals called krill, and they can be found in oceans around the world. Their immense size and distinctive appearance make them a fascinating species within the animal kingdom.