Small, aloricate ciliates with equivalent spherical cell diameters <20 µm (biovolume <4,000 µm3) compose, on average, 4–57% of the total biomass of heterotrophic (apochlorotic) nanoplankton in diverse marine systems. Biomass production of nanoplanktonic ciliates in a southeastern U.S. estuary was also a significant part of the total production of heterotrophic...