A flexible, unpaired, hollow tube found in hemichordates that arises in embryonic development as an outpocketing from the roof of the embryonic gut anterior to the pharynx. In adults, they extend dorsally from the pharynx into the probiscis, and serve to communicate with the oral cavity. [ http://en.wikipedia.org/wiki/Stomochord http://www.ncbi.nlm.nih.gov/pubmed/25214631 ]