Sperm Whale - It is the 3rd largest whale and the largest toothed whale. It is also known as common cachalot. It is the only member of genus physeter with a length of 16 m which can expand to 20.5 m; its head is one third of its body. It is the deepest diving mammal and can plunge 3km deep into water to catch its prey. Not only this, the mammal is the known to be producer of loudest sound under water as its echolocation can be loud as 230 db underwater.