The North Atlantic right whale has a large head which can take up ¼ of its total body length with a strongly arched mouth line. It has callosities situated on its lower head and lip, these can be pink, yellow or orange in colour due to whale lice living on them. Researchers can tell individuals apart by the shape of the callosities. They have large paddle-shaped pectoral fins and the largest testes in the world, with each teste weighing about a tonne.