Vetulicolia is a group of bilaterian marine animals encompassing several extinct species from the Cambrian,[2] and possibly Ediacaran,[1] periods.

[6] The taxon name, Vetulicolia, is derived from the type genus, Vetulicola, which is a compound Latin word composed of vetuli "old" and cola "inhabitant".

[7] 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.

[11] From their superficially tadpole-like forms, leaf or paddle-shaped tails, and various degrees of streamlining, it is assumed that all vetulicolians discovered to date were swimming animals that spent much, if not all, of their time living in water.

[13] The phylum Vetulicolia was erected in 2001 to group the genera Vetulicola, Didazoon, and Xidazoon (later deemed a junior synonym of Pomatrum).

[14] Prior to this the class Vetulicolida had been defined in 1997 to group Vetulicola with the previously enigmatic genus Banffia due to its similar two-part construction, as well as apparent gill slits in a newly discovered specimen.

[15] Further work split Banffia into a separate class called Banffozoa, which was soon expanded to encompass similar species such as Heteromorphus.

[14] A 2024 phylogenetic analysis by Mussini and colleagues found vetulicolians to be a paraphyletic group of stem-chordates, lying outside a clade formed by Yunnanozoon, Cathaymyrus, Pikaia and crown-chordates.

If proven true, pharyngeal slits would no longer require a deuterostome placement and vetulicolians could prove to be stem protostomes that lost the post-anal tail.

[17] However, ascidian larvae have been noted to have endoderm extending to the terminal end, which could suggest that tunicates also lacked post-anal tails ancestrally.

[11] Some workers have questioned the inclusion of Banffozoa within this group due to their lack of gill slits and apparent gut diverticula, and have theorized that they may fit within Protostomia instead.

[17] Additionally, a comprehensive review of the Vetulicolia in 2007 did not find evidence of gut diverticula in their material while acknowledging the previous report regarding Banffia.