femtoplankton

Noun

 * 1) The plankton composed of cells smaller than 0.2 micrometers.

Coordinate terms

 * megaplankton (>20cm), macroplankton (2-20 cm), mesoplankton (0.2-20mm), microplankton (20-200μm), nanoplankton (2-20μm), picoplankton (0.2-2μm), femtoplankton (<0.2μm)