The vetulicolian body plan comprises two parts: a voluminous rostral (anterior) forebody, tipped with an anteriorly positioned mouth and lined with a lateral row of five round to oval-shaped openings on each side, which have been interpreted as gills (or at least orifices in the vicinity of the pharynx); and a caudal (posterior) section that primitively comprises seven body segments and functions as a tail. All vetulicolians lack preserved appendages of any kind, having no legs, feelers or even eye spots.[5] The area where the anterior and posterior parts join is constricted.[6]
Their taxonomic affinity has been uncertain; they have been considered to represent stem- and crown-grouparthropods, stem-group vertebrates,[7] and early deuterostomes (a group which as a whole includes the vertebrates, other invertebratechordates, echinoderms and hemichordates). The general scientific consensus before 2001 considered them early limbless arthropods but now considers them early deuterostomes.[8] Vetulicolian fossils examined in 2014 show the presence of notochord-like structures, and it was concluded that vetulicolians are crown-group chordates and probably related to modern tunicates.[9] Research from 2017 rather indicates vetulicolians are related to Saccorhytus, another basal deuterostome group,[10] although another study shows possibility that Saccorhytus is ecdysozoan instead of deuterostome.[11]
Cite error: There are <ref group=note> tags on this page, but the references will not show without a {{reflist|group=note}} template (see the help page).
^Dominguez, Patricio and Jeffries, Richard. (2003). Fossil evidence on the origin of appendicularians. Paper read at International Urochordate Meeting 2003. Abstract at [2] – URL retrieved June 22, 2006.