Vol. 6 edited by Arthur C. Giese, John S. Pearse, and Vicki B. Pearse.
Contents:
v. 1. Acoelomate and pseudocoelomate metazoans.--v. 2. Entoprocts and lesser coelomates.--v. 3. Annelids and echiurans.--v. 4. Molluscs: gastropods and cephalopods.--v. 5. Molluscs: pelecypods and lesser classes.--v. 6. Echinoderms and lophophorates.--v. 9. General aspects: seeking unity in diversity