Question: What parts of the body are found at the anterior end and the base of the tail?
About the article "Anatomy", section "Vertebrate anatomy".

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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.
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. 
Its body is spirally coiled and darkly coloured (due to eel blood inside the nematode's intestine).
It is fusiform, tapering to both ends; anterior end of the body is bottle-shaped, while the posterior end is narrowed and conical.
The epicuticle is finely wrinkled, with a network structure, forming an irregular fine transparent coating.
The cuticle of the anterior andposterior parts of its body bear several papilla-like excrescences of a fibrous structured.
Its head end is rounded, being separated by a slight constriction in front of the nerve ring.
The entire anterior narrowed part of its body is approximately twice as long as the oesophagus.
Four dorso- and ventro-lateral papillae and two small lateral amphids are present.
The mouth is conspicuously depressed, the anterior margin of the buccal ca.psule being 0.027mm-0.030mm from the anterior extremity; the mouth opening is circular.
The buccal capsule is well sclerotised, trapezium-shaped in lateral view, its anterior rim bearing one row of 26 circular teeth.
Its oesophagus is strongly muscular and expanded at its posterior half, its lumen being triangular.
The valvular apparatus of the oesophagus is well developed.
The excretory pore is located near the junction of the oesophagus and intestine.
The intestine is dark, almost straight, broad, being narrowed at its anterior and posterior ends only.
Three conspicuously large oval unicellular rectal glands are present, one dorsal and two subventral.
The tail is conical and short.
The length of the male body is ; in females it ranges between . 
All vertebrates are built along the basic chordate body plan: a stiff rod running through the length of the animal (vertebral column or notochord), with a hollow tube of nervous tissue (the spinal cord) above it and the gastrointestinal tract below.
In all vertebrates, the mouth is found at, or right below, the anterior end of the animal, while the anus opens to the exterior before the end of the body.
The remaining part of the body continuing after of the anus forms a tail with vertebrae and spinal cord, but no gut. 
The lesser wings of the sphenoid or orbito-sphenoids are two thin triangular plates, which arise from the upper and anterior parts of the body, and, projecting lateralward, end in sharp points 1. 
The longest male and female found had a total length of respectively.
The head (top, sides, upper portion of the rostral scales and upper portions of the supralabial scales) of adults is olive, grayish or gray-brown in color.
32 to 36 maxillary teeth are present.
The upper (dorsal) coloration varies between grayish, gray-olive, brown-olive, brown and olive.
The anterior end of the dorsum is usually grayish, whereas the posterior two thirds of body and tail are brownish.
The subcaudal scales (scales below the tail) are immaculate yellow in color.
There are 2 to 10 scale rows in males and 2 to 6 in females, with a maximum of 12 scale rows at midbody.
The ventral (belly) scales number from 163 to 181.
A longitudinal ridge (keel) is present along the backs of females.
Subadults and some adults have faint whitish crossbands, which are remnants of the juvenile pattern, on the body and the tail.