ABSTRACT
For the first two categories, information has generally been obtained from the study of intact whole cells and ultrathin sections, and both transmission electron microscopy (TEM) and scanning electron microscopy (SEM) have made a major contribution. For the third category of studies, information has come principally from TEM studies of sectioned material, although other specialized techniques and electron microscopes have been used. Two methods of concentrating pelagic protists are commonly used: centrifugation and filtration. Filtration is generally less disruptive to deticate cells and if used carefully it can be used for quantitative estimates of cell concentrations. Since all particles in a known volume of liquid are deposited on the membrane surface it should be possible to obtain reasonably accurate quantitative assessments of species concentrations. Advantages of preparing whole mounts for TEM are that it is a rapid and relatively easy technique and excellent for qualitative identification purposes; loaded grids can be stored for years.
