Ecdysozoans are a group of invertebrates that can periodically shed and replace the body epidermis. They are the most diverse and abundant taxa in the animal kingdom, and successfully occupy various ecological niches in the Earth’s biosphere. The extant Ecdysozoa contain eight phyla, which can be divided into two main groups in terms of bodyplans: one is the vermiformic Ecdysozoans showing introvert-trunk differentiation, mouth and anus; the other is the Panarthropoda bearing with segmented trunk with paired appendages. Recent studies have found that the microfossil Saccorhytida, which has a sac-like body with a ventral mouth but no anus, represent a more primitive body configuration of early molting animals. The Panarthropoda is the most advanced in comparison with vermiformic Ecdysozoans and Saccorhytida. All three body plans (sac-type, vermiformis type and limb-bearing type) emerged during the Cambrian explosion and evolved independently.