The stomochord is a flexible, hollow tube found in hemichordates.
In adults, they extend dorsally from the pharynx into the proboscis, and it communicates with the oral cavity.
[1] Stomochords were initially considered a variant of a primitive notochord, a defining feature of chordates.
However, they are now recognized to not share histological composition to that of the notochord found in chordates, lacking the fibrous sheath characteristic of a notochord.
[1] In addition, gene expression studies have failed to provide any evidence for homology between the notochord and the stomochord, or between the notochord and any hemichordate structure.