ABSTRACT
The organelle that we now call the contractile or pulsating vacuole (CV) was first seen by Spallanzani in 1776 and has since then been described by microscopists and protistologists in great detail. Other names associated with the CV were the water expulsion vesicle of Amoeba proteus1-2 and nephridial or excretory apparatus of protozoa.36 Most CVs are delimited by a single membrane (Figures 1 and 2). Dinoflagellates, however, have an expulsion vesicle with a double membrane, and this vesicle is called a pusule (see Figure 9).7,8 Patterson9 has done an excellent job of describing available information on the morphology, ultrastructure, and function of CVs using data from a variety of protistan sources. Examination of his bibliography indicates, however, that the overwhelming majority of CV studies were done with protozoa, and therefore most of what we know about CVs is based on that group of microorganisms. In this chapter, I propose to describe the CV of microalgae and, where possible, to emphasize any differences or similarities that may exist between the CV of algae and other eukaryotic microorganisms.
