Pomatrum

Xidazoon Temporal range: Lower Cambrian
Artist's concept of Xidazoon stephanus
Scientific classification
Kingdom:	Animalia
Phylum:	Vetulicolia Shu, et al. 2001
Order:	Vetulicolida Chen & Zhou 1997
Family:	Didazoonidae Shu & Han 2001
Genus:	Xidazoon Shu, Conway Morris & Zhang 1999
Species:	X. stephanus
Binomial name
Xidazoon stephanus

The genus Xidazoon was erected by Shu, et al. (1999) based on fossils found in the Qiongzhusi (Chiungchussu) Formation, Yu'anshan Member (Eoredlichia zone), Lower Cambrian, Haikou, (Kunming), about 50 km west of Chengjiang, China. It currently consists of the single species Xidazoon stephanus.

The fossils show that the body of the animal was divided into two parts. The anterior part of the body is moderately inflated, with a prominent mouth circlet. It has faint transverse divisions towards the front, but is otherwise smooth. The mouth circlet consists of about 30 plates divided into inner and outer regions. The anterior section has five structures on each side, which are interpreted as gills. A dark region running close to the ventral and posterior margins is interpreted as an endostyle. The condition of the anterior portion of the fossils suggests that it was thin-walled, i.e., that the anterior portion was largely hollow. The posterior part of the body tapers towards front and back (diamond-shaped), and is divided into seven segments covered in cuticle with three less well-defined segments at the anterior end. There are short spines at the posterior tip. The authors describe an alimentary canal with terminal openings and a rectum with what might be dilator muscles.

On account of an examination of the incomplete/damaged holotype, and comparison with the incomplete/damaged holotype of Pomatrum ventralis, researchers Aldridge, et al., proposed that X. stephanus was a junior synonym of P. ventralis on account of how the anterior portions of both species are largely identical. However, other researchers point out that, although the anterior portions may be extremely similar, the posterior portions of the carapaces differ in shape and width, and, more importantly, the tails differ greatly, in that in X. stephanus, it is composed of seven segments and leaf- or diamond-shaped, while in P. ventralis, the tail is oar-shaped, and is composed of many more segments, especially near its base.

See also

• Maotianshan shales

References

• Shu, D.-G., Conway Morris, S., Zhang, X.-L., Chen, L., Li, Y. and Han, J. 1999. A pipiscid-like fossil from the Lower Cambrian of south China, Nature, 400:746-749. (August 19, 1999). [1] - URL retrieved December 1, 2005.
• Shu, D.-G., Conway Morris, S., Han, J., Chen, L., Zhang, X.-L., Zhang, Z.-F., Liu, H.-Q., Li, Y., and Liu, J.-N. 2001. Primitive Deuterostomes from the Chengjiang Lagerstätte (Lower Cambrian, China), Nature, 414:419-424. (November 11, 2001). [2]. - URL retrieved December 2, 2005

External links

• New phylum on the block
• Once We Were Worms
• Chu, et al., Primitive Deuterostomes from the Chengjiang Lagerstätte