Euplotes daidaleos ≤2,500: Halteria viridis ≤700 cells/ml
||Esteban GF, Fenchel T, Finlay BJ. Mixotrophy in ciliates. Protist. 2010 Dec161(5):621-41. doi: 10.1016/j.protis.2010.08.002 p.631 left column bottom paragraphPubMed ID20970377
||B.J. Finlay, S.C. Maberly, G.F. Esteban Spectacular abundance of ciliates in anoxic water:contribution of symbiont photosynthesis to host respiratory oxygen requirements FEMS Microbiol Ecol, 20 (1996), pp. 229-235 link
||P.631 left column bottom paragraph: "In some ciliates, oxygenic photosynthesis of the algal endosymbionts creates a source of oxygen, especially so under low light levels (Reisser 1987). The freshwater ciliates Euplotes daidaleos and Halteria viridis are a text–book example of such O2 evolving syntrophic associations. Both ciliate species harbour symbiotic Chlorella (Fig. 1). The cytoplasm of H. viridis also harbours green particles (unidentifiable under light microscopy) that, although their ultrastructure has not been investigated, resemble sequestered chloroplasts (Fig. 1). During warm summers, these two ciliate species alone can reach abundances of 2,500 and 700 cells per ml, respectively (primary source). Such peak of abundance in their vertical distribution in the stratified water column occurs at a depth where dissolved oxygen is not detectable. The phototrophic endosymbionts, by producing oxygen, seem to enable E. daidaleos and H. viridis to survive at greater depths than they would otherwise be able to do."