, issued in two parts, is the sixth volume in the series. Part A: Porifera through Mollusca Contents Series Preface; Preface to Volume VI; Systematic Resume of the Invertebrates; Porifera, Paul E. Fell; Cnidaria, Stanley Shostak; Platyhelminthes-Turbellaria, Mario Benazzi and Giuseppina Benazzi Lentati; Platyhelminthes-Trematoda, Roy M. Anderson; Platyhelminthes-Eucestoda, Larry S. Roberts and C. R. Kennedy; Mesozoa, Bayard H. McConnaughey; Rotifera, John J. Gilbert; Gastrotricha, M. R. Hummon and W. D. Hummon; Acanthocephala, C. R. Kennedy; Sipuncula, Mary E. Rice and John F. Pilger, Mollusca, N. W. Runham; Species Index; Subject Index. Part B: Annelida-Clitellata through Cephalochordata Contents Series Preface; Preface to Volume VI; Systematic Resume of the Invertebrates; Annelida-Clitellata, B. Christensen; Tardigrada, Roberto Bertolani; Arthropoda-Crustacea, T. J. Pandian; Arthropoda-lnsecta, J. Muthukrishnan; Pentastomida, J. Riley; Bryozoa Entoprocta, C. Nielsen; Brachiopoda, S. H. Chuang; Chaetognatha, A. Alvariño; Echinodermata: Asexual Propagation, Philip V. Mladenov and R. D. Burke; Hemichordata, J. A. Petersen; Cephalochordata, Jaypaul Azariah; Species Index; Subject Index.