Speciation in the open ocean

Species inhabiting the open oceans generally occupy broad distribution ranges, extending from parts of ocean basins to entire oceans1. Such oceanic species are accepted as monospecific because of their tendency to be dispersed across great distances by ocean currents. Indeed, there are few known examples of cryptic diversity among species in the oceanic environment2. We have now found large, localized genetic differences within a circumglobal, monotypic species of deep-sea fish. This shows that cryptic allopatric lineages can and have split without discernible barriers, suggesting that there might have been a serious underestimation of oceanic biological diversity.