Xidazoon
Encyclopedia
The genus Xidazoon was erected by Shu, et al. (1999) based on fossil
s 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.
Based on a comparison of the incomplete/damaged holotype with the incomplete/damaged holotype of Pomatrum ventralis, researchers Aldridge, et al., proposed that X. stephanus was a junior synonym of P. ventralis because the anterior portions of the two 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.
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s found in the Qiongzhusi (Chiungchussu) Formation, Yu'anshan Member (Eoredlichia zone), Lower Cambrian, Haikou, (Kunming
Kunming
' is the capital and largest city of Yunnan Province in Southwest China. It was known as Yunnan-Fou until the 1920s. A prefecture-level city, it is the political, economic, communications and cultural centre of Yunnan, and is the seat of the provincial government...
), about 50 km west of Chengjiang, China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
. 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
Mouth
The mouth is the first portion of the alimentary canal that receives food andsaliva. The oral mucosa is the mucous membrane epithelium lining the inside of the mouth....
circlet. It has faint transverse
Transverse plane
The transverse plane is an imaginary plane that divides the body into superior and inferior parts. It is perpendicular to the coronal and sagittal planes....
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
Endostyle
An endostyle is a longitudinal ciliated groove on the ventral wall of the pharynx which produces mucus to gather food particles. It is found in urochordates and cephalochordates, and in the larvae of lampreys. It aids in transporting food to the esophagus. It is also called the hypopharyngeal groove...
. 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
Cuticle
A cuticle , or cuticula, is a term used for any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticles" are non-homologous; differing in their origin, structure, function, and chemical composition...
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.
Based on a comparison of the incomplete/damaged holotype with the incomplete/damaged holotype of Pomatrum ventralis, researchers Aldridge, et al., proposed that X. stephanus was a junior synonym of P. ventralis because the anterior portions of the two 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.