Editing Sipuncula (section)

===Digestive system===
The [[digestive tract]] of sipunculans starts with the esophagus, located between the introvert retractor muscles. In the trunk the intestine runs posteriorly, forms a loop and turns anteriorly again. The downward and upward sections of the gut are coiled around each other, forming a [[double helix]]. At the termination of the gut coil, the [[rectum]] emerges and ends in the [[anus]], located in the anterior third of the trunk. Digestion is [[Extracellular digestion|extra-cellular]], taking place in the lumen of the intestine. A rectal caecum, present in most species, is a blind ending sac at the transition between intestine and rectum with unknown function. The anus is often not visible when the introvert is retracted into the trunk.<ref name=IZ/>