Unveiled the mystery of the origin of the posterior-mouthed animal "Earth Worm" - Prehistoric Creatures Illustrated 020 Earth Worm

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

Distribution area: China (Chengjiang biota, Yunnan Province)

The earthworm is about 20 cm long and is a primitive hindquarter discovered and named by Professor Shudgan et al. in the history of life evolution. Shu Degan dedicated his genus name to his alma mater, China University of Geosciences (Beijing), and the name honored his esteemed mentor, Academician Hao Yichun. Fossil characteristics of the earthworm: the body is clearly divided into anterior and posterior parts, the anterior part of the body is 6 segments, the mouth is wide, and the edge of the abdomen is flat. On each side of the anterior part of the body are five ovate structures representing gill sacs, each with a shroud-like opening that appears to be connected to the inside of the body. The posterior part of the body (tail) is divided into 7 segments and is broad-leaf-shaped. Internal dissection shows that the esophagus is enlarged in the anterior part of the body and has a narrow , straight ( occasionally circling ) bowel shape in the posterior part. A dark cord developing along the abdomen in the anterior part may represent its inner column. The ground worm represents a very critical link in the evolutionary history of the early proto-orzoan to hind-mouth animal lineage. Its discovery and the determination of its special place in the evolutionary tree of life allow us to initially unveil the mystery of the origin of the posterior-mouthed animals.

The basic feature of morphological anatomy of the archaea phylum is the segmentation of the body, which consists of two parts: the anterior and posterior bodies. The precursor is digestion

The anterior segment of the road (pharynx), which can be divided into the dorsal and ventral regions, is separated by the gill region consisting of 5 pairs of gill sacs; the posterior body (tail)

It is the posterior segment of the digestive tract (i.e., the intestine), the terminal anus. The vast majority of archaea consist of 7 or more body segments,

It consists of three parts, namely the central axial region and its flat dorsal and ventral lobes formed by its extension to the dorsal and ventral sides, respectively; the central axial region and the dorsal lobe and the ventral lobe

The ventral lobes maintain segmented consistency.