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.^[1][2] It may be paraphyletic,^[3] even if the phylum Vetulicolia is monophyletic.^[4]

Didazoonidae Temporal range: Cambrian Stage 3 PreꞒ Ꞓ O S D C P T J K Pg N
Didazoon haoae Pomatrum ventralis Yuyuanozoon magnificissimi Artists' reconstructions of Didazoonids
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade?:	†Vetulicolia
Class:	†Vetulicolida
Order:	†Vetulicolata
Family:	†Didazoonidae Shu and Han in Shu et al. 2001
Type genus
†Didazoon Shu and Han in Shu et al. 2001
Genera
†Didazoon Shu and Han in Shu et al. 2001 †Pomatrum Luo and Hu, in Luo et al. 1999 †Yuyuanozoon Chen, Feng and Zhu in Chen et al. 2003 ? †Nesonektris García-Bellido et al. 2014

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.^[2]

Taxonomy

Didazoonidae was erected to group Didazoon. Xidazoon. and Pomatrum, although Xidazoon has since been shown to be a junior synonym of Pomatrum.^[1] Yuyuanozoon was moved to the Didazoonidae after additional specimens illuminated more details of the anterior opening and posterior segment annulations.^[5]

Nesonektris has also been assigned to Didazoonidae by some workers,^[6] but this has not been widely accepted.^[7][8]

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:^[3]

Chordata	Banffia† Heteromorphus† Skeemella† Nesonektris† Vetulicolidae† Didazoon† "Didazoonidae" Pomatrum† Yuyuanozoon† Yunnanozoon† 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:^[4]

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

References

1. Aldridge et al. 2007, pp. 145–146
2. Li et al. 2018, p. 1085 (Note: This paper uses different terminology for vetulicolian anatomy explained on page 1082; this page uses the more common terms regardless of source)
3. Mussini et al. 2024, pp. 6–7 (Note: The cladogram is simplified using the definition of Vetulicolidae from Li et al. 2018, cited elsewhere on this page)
4. García-Bellido et al. 2014, p. 9
5. Li et al. 2018, p. 1082
6. Li et al. 2018, p. 1084
7. "†Nesonektris García-Bellido et al. 2014". Paleobiology Database. Retrieved December 8, 2024.
8. "†family Didazoonidae Shu and Han 2001". Paleobiology Database. Retrieved December 8, 2024.

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:10.1111/j.1475-4983.2006.00606.x. S2CID 85722738.
• 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:10.1111/j.1755-6724.2003.tb00742.x. S2CID 128895860.
• García-Bellido, Diego C.; Lee, Michael S. Y.; Edgecombe, Gregory D.; Jago, James B.; Gehling, James G.; Paterson, John R. (2014). "A new vetulicolian from Australia and its bearing on the chordate affinities of an enigmatic Cambrian group". BMC Evolutionary Biology. 14: 214. doi:10.1186/s12862-014-0214-z. PMC 4203957. PMID 25273382.
• 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:10.1017/jpa.2018.18.
• Mussini, G.; Smith, M. P.; Vinther, J.; Rahman, I. A.; Murdock, D. J. E.; Harper, D. A. T.; Dunn, F. S. (2024). "A new interpretation of Pikaia reveals the origins of the chordate body plan". Current Biology. 34 (13): 2980–2989.e2. doi:10.1016/j.cub.2024.05.026. PMID 38866005.
• 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:2001Natur.414..419S. doi:10.1038/35106514. ISSN 0028-0836. PMID 11719797. S2CID 4345484.