Introduction and Progress in the Last Half Century

Abstract

The history of ciliate systematics has been divided into fi ve periods: (1) the Age of Discovery; (2) the Age of Exploitation; (3) the Age of Infraciliature; (4) the Age of Ultrastructure; and (5) the Age of Refi nement. Progress in each of these periods arose through an interaction of technology and conceptual views. For example, refi ned silver staining techniques revealed the law of desmodexy of the ciliate cortex and enabled the development of comparative morphogenetics in the Age of Infraciliature. Electron microscopy was essential for the conceptual notion of levels of organization below the cell and provided the impetus for the structural conservatism hypothesis in the Age of Ultrastructure. In this latter age, the foundations for the current classifi cation system have been laid. Gene sequencing has provided the next technological innovation, which has enabled testing and revising our views on relationships in the current Age of Refi nement. Major differences between the scheme presented herein with its two subphyla and 11 classes and other competing schemes are briefl y discussed.