Since their origin in the Ordovician, ostracods have radiated to several different aquatic and even semiterrestrial environments, evolving under influence of both extrinsic (ecological) and intrinsic (genetic) factors. The deep ocean does not constitute an exception to these controls, no matter how different the concept of deep-sea might be among students of Paleozoic and post-Paleozoic ostracods. Once integrated to the bathybic biotas (i.e., from bathyal to abyssal depths, including guyots), ostracods followed a particular pattern of diversification and dispersal in response to climatic and tectonic events.