The Bowhead Whale is one of the largest whales on Earth and it has the largest mouth of any creature on the Planet.

A Bowhead Whale Spy-Hopping In The Ulbansky Bay, Northwestern Okhotsk Sea (Author: Olga Shpak/Wikimedia Commons cc by-sa 3.0)
The Bowhead Whale is one of the biggest whales on earth and it’s a species belonging in the Balaenidae family. They live exclusively in the waters of the Arctic and sub-Arctic regions of the Earth.
It has a dark, stocky body, with a white patch under its lower jaw and it lacks a dorsal fin. Their heads are large, triangular, and so strong that they use them to break through thick sheets of ice in order to breath. Some Inuit hunters have even reported seeing bowhead whales breaking through up to 60 cm (24 in) of solid ice.
This whale gets its common name from its strongly bowed lower jaw and narrow upper jaw. These are filter feeders: instead of teeth, they have baleen plates for filtering prey after gulping large amounts of water. Interestingly, the bowhead whale has the largest baleen plates of any whale: about 3 m (9.8 ft).