Didazoonidae

Didazoonidae is a vetulicolian family within the order Vetulicolata. It is characterized by a relatively thin-walled, non-biomineralized body and a large, round anterior opening surrounded by an oral disc. It may be paraphyletic, even if the phylum Vetulicolia is monophyletic.

Description

Didazoonids have an ovoid to subquadrate anterior section divided into six subdivisions marked by five circumventing lines perpendicular to the body axis. Cowl-shaped lateral pouches appear along each side of the anterior section, coincident with the five dividing lines. The anterior opening is large, round, and surrounded by a circumventing oral disc. The posterior section has seven segments, which in some species each carry up to six annulations.

Taxonomy

Didazoonidae was erected to group Didazoon. Xidazoon. and Pomatrum, although Xidazoon has since been shown to be a junior synonym of Pomatrum. Yuyuanozoon was moved to the Didazoonidae after additional specimens illuminated more details of the anterior opening and posterior segment annulations.

Nesonektris has also been assigned to Didazoonidae by some workers, but this has not been widely accepted.

A 2024 study has found the Didazoonidae (without Nesonektris) to be a paraphyletic grade of the vetulicolians closest to crownward chordates as shown in this simplified cladogram:

Chordata	Banffia† Heteromorphus† Skeemella† Nesonektris† Vetulicolidae† Didazoon† "Didazoonidae" Pomatrum† Yuyuanozoon† Yunnanozoon† Cathaymyrus† Pikaia† Chordata (crown group)
	Banffia†

	Heteromorphus†

	Skeemella† Nesonektris† Vetulicolidae† Didazoon† "Didazoonidae" Pomatrum† Yuyuanozoon† Yunnanozoon† Cathaymyrus† Pikaia† Chordata (crown group)
	Skeemella†

	Nesonektris† Vetulicolidae† Didazoon† "Didazoonidae" Pomatrum† Yuyuanozoon† Yunnanozoon† Cathaymyrus† Pikaia† Chordata (crown group)
	Nesonektris†

	Vetulicolidae† Didazoon† "Didazoonidae" Pomatrum† Yuyuanozoon† Yunnanozoon† Cathaymyrus† Pikaia† Chordata (crown group)
	Vetulicolidae†

	Didazoon† "Didazoonidae" Pomatrum† Yuyuanozoon† Yunnanozoon† Cathaymyrus† Pikaia† Chordata (crown group)
	Didazoon†	"Didazoonidae"

	Pomatrum†

	Yuyuanozoon†

	Yunnanozoon† Cathaymyrus† Pikaia† Chordata (crown group)
	Yunnanozoon†

	Cathaymyrus† Pikaia† Chordata (crown group)
	Cathaymyrus†

	Pikaia†

	Chordata (crown group)







(total group)

An earlier study in 2014 placed vetulicolians as the sister-group to tunicates, but was unable to resolve any relationships among vetulicolians as a group:

Vetulicolia†	Vetulicola† Beidazoon† Ooedigera† Pomatrum† / Xidazoon† "Didazoonidae" Didazoon† Yuyuanozoon† Banffia† Heteromorphus† Nesonektris†
	Vetulicola†

	Beidazoon†

	Ooedigera†

	Pomatrum† / Xidazoon†	"Didazoonidae"

	Didazoon†

	Yuyuanozoon†

	Banffia†

	Heteromorphus†

	Nesonektris†


	Tunicata

Works cited

Aldridge, Richard J.; Hou, Xian-guang; Siveter, David J.; Siveter, Derek J.; Sarah E., Gabbott (2007). "The systematics and phylogenetic relationships of vetulicolians". Palaeontology. 50: 131–168. doi:. S2CID .
Chen, Ailin; Feng, Hongzhen; Zhu, Maoyan; Ma, Dongsheng; Li, Ming (2003). "A New Vetulicolian from the Early Cambrian Chengjiang Fauna in Yunnan of China". Acta Geologica Sinica. 77 (3): 281–287. doi:. S2CID .
García-Bellido, Diego C.; Lee, Michael S. Y.; Edgecombe, Gregory D.; Jago, James B.; Gehling, James G.; Paterson, John R. (2014). . BMC Evolutionary Biology. 14: 214. doi:. PMC . PMID .
Li, Yujing; Williams, Mark; Gabbott, Sarah E.; Chen, Ailen; Cong, Peiyun; Hou, Xianguang (2018). "The enigmatic metazoan Yuyuanozoon magnificissimi from the early Cambrian Chengjiang Biota, Yunnan Province, South China". Journal of Paleontology. 92 (6): 1081–1091. doi:. hdl:.
Mussini, G.; Smith, M. P.; Vinther, J.; Rahman, I. A.; Murdock, D. J. E.; Harper, D. A. T.; Dunn, F. S. (2024). . Current Biology. 34 (13): 2980–2989.e2. doi:. hdl:. PMID .
Shu, D. G.; Conway Morris, S.; Han, J.; Chen, L.; Zhang, X. L.; Zhang, Z. F.; Liu, H. Q.; Li, Y.; Liu, J. N. (November 22, 2001). "Primitive deuterostomes from the Chengjiang Lagerstätte (Lower Cambrian, China)". Nature. 414 (6862): 419–424. Bibcode:. doi:. ISSN . PMID . S2CID .