This volume, 9A, contains the material on the euphausiaceans, amphionidaceans, and many of the decapods (dendrobranchiates, carideans, stenopodideans, astacidans, and palinurans). With the publication of this ninth volume in the Treatise on Zoology: The Crustacea, we depart from the sequence one would normally expect. Some crustacean groups never had a French version produced, namely, the orders Stomatopoda, Euphausiacea, Amphionidacea, and Decapoda; the largest contingent of these involved Decapoda – a group of tremendous diversity and for which we have great depth of knowledge. The organization and production of these “new” chapters began independently from the other chapters and volumes. Originally envisioned by the editorial team to encompass volume 9 of the series, it quickly became evident that the depth of material for such a volume must involve the printing of separate fascicles. These new chapters are now nearing completion, and the decision was made to begin publication of volume 9 immediately rather than wait until after volumes 3 through 8 would appear.