The southern right whale (Eubalaena australis) is a baleen whale, one of three species classified as right whales belonging to the genus Eubalaena. Approximately 10,000 southern right whales are spread throughout the southern part of the Southern Hemisphere. Like other right whales, the southern right whale is readily distinguished from others by the callosities on its head, a broad back without a dorsal fin, and a long arching mouth that begins above the eye. Its skin is very dark grey or black, occasionally with some white patches on the belly. The right whale's callosities appear white due to large colonies of cyamids, or whale lice. It is almost indistinguishable from the closely related North Atlantic and the North Pacific right whales, displaying only minor skull differences. It may have fewer callosities on its head than North Atlantic and more on its lower lips than the two northern species. The biological functions of callosities are unclear, although the primal role has been considered to be for protection against predators.