In oceanic waters the vast majority of the species of planktonic ostracods are halocyprids. They are often very abundant, numerically ranking second only to copepods in abundance in mesoplankton samples particularly in subthermocline waters. In the water column they are nearly ubiquitous, occurring almost everywhere from the surface to abyssal depths. However, at high latitudes (>50°C) they are seldom encountered in the upper 100-200m of the water column, although they are very abundant in deeper waters. For example, they are infrequently sampled in low numbers by the Continuous Plankton Recorder, which is routinely towed at 8 -10m (Williams, 1975). Their relatively small size (0.5 -> 3mm) means that despite their numerical abundance, they seldom make a substantial contribution to the overall planktonic biomass. Most of the halocyprid species are detritivores, seemingly adapted to exploit marine snow and other sinking particles.
We present a listing of the currently recognized species, including the new systematics of the ‘Metaconchoecia’ that is currently in press. In inshore waters, particularly in the tropics 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. The majority of these myodocopid species are meroplanktonic, and only enter the water column at certain stages of their life histories.