蜕皮动物是一类能周期性蜕掉和更换身体表皮的无脊椎动物，是动物界生物多样性最高、数量最多的类群，并且成功占据了地球生物圈的各种生态位。现存的蜕皮动物包含八个门，从躯体构型上可分为两大类：其一为具吻-躯干分化、有口有肛门的、无附肢的蠕形蜕皮动物；其二为发育成对附肢型的泛节肢动物。最新研究发现，无“头-躯干分化”、外形呈囊 状、有腹部口而无肛的，保存为微体化石的皱囊动物门代表了一类早期蜕皮动物更为原始的躯体构型，而有附肢型更为先 进。三大躯体构型(囊型、蠕虫型、有附肢型)在寒武纪大爆发期间均已经出现，并独立演化。

 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.