The reporter learned from Northwestern University that a joint study by the Chinese and French teams has revealed a new advanced taxonomic unit of molting animals in the early Cambrian period in China, namely the wrinkled sac animal phylum, which is composed of wrinkled sac animals and Beresia, and has denied the view that wrinkled sac animals are simplified from worm like circular neural animals with terminal ports. It is reported that molting animals are the most abundant and diverse invertebrates on Earth, occupying various ecological niches on land, sea, and air. They are named after experiencing multiple molting processes during their growth and development. The body of molting animals generally consists of a head and a trunk, forming a long strip shape. The body structure of extant and known fossil molting animals suggests that the common ancestor of molting animals may have a worm like structure, and the trunk does not develop legs, with the snout located at the front end of the body (referred to as the terminal port). In recent decades, the discovery of fossilized molting animals with well-developed terminal ports throughout the entire Cambrian period, and even the earliest Cambrian period (535 million years ago), also supports this viewpoint. However, the discovery of miniature cystic molting animals with mouths but no anus in the Cambrian lucky period strata in southern Shaanxi, approximately 535 million years ago, does not support this hypothesis. The discovery of wrinkled cysticercosis suggests that in the early stages of molting animal evolution, in addition to the worm like form, there were also cystic forms. Although some paleontologists still believe that the mouth of wrinkled cysticercosis is located at the forefront of the body rather than the ventral side based on individual specimens. The above two opposing views raise several questions: is the mouth located in the abdomen or at the forefront? Which is the earliest appearance of cystic or worm like configurations? What is the body structure of the common ancestor of molting animals? Recently, a research team led by Professor Guo Junfeng from Chang'an University discovered a microfossil Beilei worm in the second Cambrian period (529 million years ago) in the Three Gorges area of Hubei Province. The length of the Beret worm ranges from 1 millimeter to 3 millimeters, as its name suggests. It has a sharp front and blunt back, low front and high back, and its overall shape resembles a Beret hat, hence its name. Its protruding curved surface covers symmetrically arranged spiny bone fragments on both sides, which are longitudinally distributed along the front and back directions of the animal. The flatter side is poorly preserved, with a large and incomplete opening visible. Morphologically, Beresia clearly belongs to bilaterally symmetrical animals. Functionally, in symmetrical benthic animals, the spiny bone fragments have a defensive effect and are mostly developed on the back. Therefore, the back is harder and easier to preserve. In addition, all symmetrical animals on both sides without exception develop their mouths. The back of the Berei worm has no mouth, so the mouth can only exist inside the incomplete opening on the abdomen. Professor Guo Junfeng from Chang'an University stated that in terms of morphology, body proportion, and distribution of bone plates, Belesia and Cystidium are very similar. However, Beresia beetles exhibit clearer dorsal and anteroposterior differentiation, such as a flatter abdomen without bone plates and fewer and more developed dorsal bone plates for defense. Obviously, the Beresia worm evolved from the wrinkled cyst worm. At present, Beresia has not directly observed the mouth, and the mouth is speculated. In future work, we hope to find direct evidence of the mouth. Han Jian, a researcher from Northwestern University, said that the results of phylogenetic analysis showed that Beresia and Cochinococcus constituted a unilineal group at least at the level of phylum - Cochinococcus, and formed a sisters group with the common ancestor of eight existing ecdysfera phyla. This result indicates that the wrinkled cysticercosis are different from the extant molting animals and may be closer to the common ancestor of molting animals. The research findings are titled "Early evolution of the ecdysozoan body plan" and published in the internationally renowned comprehensive biological journal eLife. Dr. Wang Deng from Northwestern University, Dr. Qiang Yaqin from Chang'an University, and Researcher Jean Vannier from the University of Lyon in France are the co first authors of this paper; Professor Guo Junfeng from Chang'an University and Researcher Han Jian from Northwest University are co corresponding authors. (Lai Xin She)