Materials included in this article were originally prepared for the book "South Atlantic Zooplankton" (D. Boltovskoy, ed.), a ca. 2,000 pages guide on the identification and distribution of 30 zooplanktonic groups to be published in 1989 by Backhuys Publishers, The Netherlands. Permission of the publisher for electronic reproduction of this chapter in PE is acknowledged. Thanks are due to the many colleagues and publishers which kindly allowed using their published and unpublished illustrations for this work, and especially to Neil Swanberg, Petrus van de Paverd, Amy Weinheimer, and Cathy Nigrini for providing several of the photographs included. Critical reviews by Cathy Nigrini, Stanley Kling and Amy Weinheimer, as well as comments by Roger Anderson, Brian O’Connor, Luis O'Dogherty, William Riedel, and Annika Sanfilippo, were helpful for improving earlier vesions of the manuscript. This work was partly financed by grants from the University of Buenos Aires (UBA EX-040), from the Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina (CONICET PID-BID 0366), and from the Agencia Nacional de Promoción Científica y Tecnológica, Argentina (BID/OC-AR-PMT-PICT0395).