Paleoceanographic and evolutionary studies of planktic foraminifera depend upon an assumption that individuals in morphologically-defined species share common ecologies and evolutionary histories. We will analyze modern planktic foraminifera using multiple genes to study the phylogeny and genetic variation in this widespread group of pelagic organisms. Our objectives are to (1) estimate the genetic biodiversity of living planktic foraminifera; (2) study the geographic and water column distribution of the major genotypes of these taxa in relation to hydrographic conditions, and (3) examine the morphological and stable isotopic characteristics of the genotypes to assess their degree of ecological distinctiveness. By integrating to the genetic analyses, ecological analyses of the oceanographic data from the collected localities, as well as stable isotopic analyses of the foraminiferal shells, we will be able to test the importance of water-masses and/or depth habitat in the evolutionary history and species distribution of planktic foraminifera. Our work will help adjust morphological species concepts to better match the genetic and ecological subdivisions of natural populations. This is a crucial requirement to create realistic paleoclimatic analyses based on foraminifer distributions and paleoclimate transfer functions as well as to understand the biodiversity and evolution of pelagic organisms.