post-abdomen

from The Century Dictionary.

• noun A posterior abdominal part of the body in any way distinguished, as in an insect or a crustacean; in mollusks, the postanal part or region of the body; in ascidians, the prolongation of the abdomen beyond the alimentary canal. The tail of a scorpion, or the telson of a king-crab, is a postabdomen. See cut under Pedipalpi.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Zoöl.) That part of a crustacean behind the cephalothorax; -- more commonly called abdomen.