The part of the body that contains the digestive and reproductive organs; the lower part of the body in front of the cloaca; belly; that portion of the body which contains the intestine and other viscera. Ventral part of the bird. Synonym(s): belly. In picture it is referred to as belly. In crustaceans, the posteriormost region of the body which includes several segments, including the tail. Often the abdominal segments have appendages for swimming, breathing, or holding eggs. The abdomen of most true crabs is held tightly folded under the thorax, while that of shrimp and lobsters is stretched out behind the thorax. In some polychaete worms, the body behind the prostomium and peristomium is divided into two dissimilar regions, an anterior thorax and a posterior abdomen. Some may also have a tail, behind the abdomen, which has small segments with no appendages. 