We review nearly 500 years of literature on the anatomy of ocean sunfishes (Molidae) and present new findings based on our extensive anatomical studies of specimens. We document similarities and differences among the three living genera, Ranzania, Masturus, and Mola, using the organ-system approach to examine general body form and external anatomy, skeleton, muscles, integument, brain and sense organs, digestive organs, heart and circulation, respiratory system, excretory system, reproductive system, and endocrine organs. Known for centuries for basking and seemingly sluggish behavior at the water’s surface, recent tagging studies on locomotion and diving behavior show that ocean sunfishes swim over great horizontal and vertical distances in the water column at higher speeds than previously thought. We interpret the evolution of many of their unusual anatomical features in light of this new information about their natural history and behavioral ecology, which helps to explain the evolution of such an extreme
