 The main difference between each family of mysticete is in their feeding adaptations and subsequent behaviour . Balaenopterids are the rorquals . These animals , along with the cetotheriids , rely on their throat pleats to gulp large amounts of water while feeding . The throat pleats extend from the mouth to the navel and allow the mouth to expand to a large volume for more efficient capture of the small animals they feed on . Balaenopterids consist of two genera and eight species . Balaenids are the right whales . These animals have very large heads , which can make up as much as 40 % of their body mass , and much of the head is the mouth . This allows them to take in large amounts of water into their mouths , letting them feed more effectively . <unk> have one living member : the gray whale . They are bottom feeders , mainly eating crustaceans and benthic invertebrates . They feed by turning on their sides and taking in water mixed with sediment , which is then expelled through the baleen , leaving their prey trapped inside . This is an efficient method of hunting , in which the whale has no major competitors . 
