Planktonic ostracods are a neglected component of mesoplanktonic communities, despite being almost ubiquitous throughout the World's oceans. Currently the number of planktonic ostracods described from oceanic waters is 203. In addition there are 34 species of the family Thaumatocyprididae, which are predominantly either benthic or cavernicolous. We present a listing of the currently recognized species . In inshore waters, particularly in the vicinity of coral reefs, there is a great diversity of myodocopid ostracods that can be sampled in the water column especially at night. Most of these myodocopid species are not holoplanktonic, entering the water column at certain stages of their life histories. This site only covers the holoplanktonic species and does not deal with any of the neritic species.
In oceanic waters the vast majority of planktonic ostracods are halocyprids. They are often very abundant, and rank second to copepods in numerical abundance particularly in subthermocline waters. They may occur almost everywhere from the surface to abyssal depths. However, they are seldom encountered in the upper 100-200m of the water column at high latitudes (>50�), for example they are infrequently sampled by the Continuous Plankton Recorder, which is towed at 8-10m (Williams, 1975). However, their relatively small size (0.5->3mm) means their contribution to the overall planktonic biomass is usually small (<5%). Most species appear to be detritivores, seemingly adapted to exploit marine snow and other sinking particulates. The group frequently goes unreported, because there is a perception that they are difficult to identify, and so they are overlooked. This difficulty is more the result of a lack of good manuals of identification, rather than any greater intrinsic difficulty of identifying them compared with most other components of the plankton. As well as the halocyprids, there are eight very striking species of carnivorous deepwater myodocopids (i.e. Gigantocypris and Macrocypridina ) that are planktonic, but only two have been recorded from the Southern Ocean.
In preparing this atlas, we have compiled a complete inventory of published records for all known species that can be geo-positioned with reasonable accuracy. These data have been supplemented with a considerable body of unpublished data derived from material collected by Discovery Investigations mostly in the 1930's (identified by MVA). Our aim is ultimately to generate a global atlas for all the species. Here as an initial step we have focused on the species that have been recorded from the Southern Ocean . The criterion whereby we have chosen to include species is a single reliable record from south of 52�S. This reduces the number of species that are predominantly associated with low latitudes, but are advected into higher latitudes via mesoscale eddies. Other authors have used lower latitudes to delimit Southern Ocean species, for example Razouls et al. (2000) in their study of the biogeography of Antarctic copepods used 45�S as the northern limit of the Southern Ocean. Our compilation for these 47 species