Tadpole "West Worm" of jawless fish archaeoptera - Prehistoric Creatures Illustrated 022 Issue West Worm

<h1>West Worm</h1>

Age of existence: Cambrian Second Unification 525 million ~ 500 million 20 million years ago

Distribution area: China (Chengjiang biota, Yunnan Province)

The body of the western insect is about 10 cm long and is a peculiar transition type between proto-mouthed animals and posterior-mouthed animals. First discovered by Shu Degan et al. in the Haikou area of Kunming, Yunnan Province, in March 1998, it was described and named in 1999. The genus name is short for Northwestern University.

The peculiarity of the Zebra is that its body consists of two parts, the posterior part is consistent with the proto-mouthed animal, while the anterior part is close to the pharyngeal cavity of the posterior-mouthed animal. In particular, the unique structure of the "double ring" large mouth at the front may have some connection with the North American Carboniferous jawless fish "Pipiscus". Therefore, Shu Degan and others rushed to the University of Birmingham in the United Kingdom to investigate the fossil specimens of leather fish preserved there. However, after repeated comparisons and discussions, it is still difficult to determine its biological status.

There are three possible final conclusions:

1. The Great Worm represents a branch of the primitive ancestors of jawless vertebrates, including skinfish;

2. Together with the skin fish, the Western worm forms a unique and extinct phylum;

3. The peculiar double ring mouth of the West Great Worm is a convergent structure.

Shudgan proposed the perfect hypothesis of the origin of vertebrates: prototozoa → archaea → echinoderms / hemizoans → tails → cephalozoa → vertebrates. Shudgan also summarized the 8 most convincing evidences for the archaeoptera phylum as a base taxon of posterior mouth animals:

1. Archaea have gill fissure structures with gill sacs and gill filaments;

2. The outer layer of the "shell" of the archaea is coated with a membrane, so it may be an endoskeleton derived from the mesoderm;

3. The body of the archaeoptera is divided into two parts;

4. The body of the archaeopterus still retains the segmented traits of the common ancestor of the original mouth and the post-mouth animal;

5. The "anterior mouth" of archaea indicates that they inherit the original traits of the common ancestor of the original mouth and the posterior mouth animals;

6. Archaea do not possess any of the unique proximate traits of arthropods;

7. The tadpole-like shapes of archaea and the inner column structure of their precursors suggest that they may be associated with caudal cordons;

8. In addition, the discovery and demonstration of archecyloid fossils in the Chengjiang Fossil Bank as the progenitor of echinoderms further supports the idea that the archaeoptera represents the most primitive class in the hindzumatome lineage.

Archaea represent a more primitive class of basal taxa than the steppers. The archaea phylum is the first group of animals on Earth to have a primitive gill fissure structure. It was the emergence of this key innovative structure of gill fissure that triggered a revolution in the basic metabolic effects of animals on both sides such as feeding and respiration, ushered in the birth of the posterior mouth animal lineage, thus laying the foundation for the emergence of vertebrates, including humans.