An investigation of growth and segmentation of a ptychopariid trilobite Maotunia iddingsi from the middle Cambrian (Miaolingian, Drumian) Zhangxia Formation, North China is presented. This is the first time the essentially complete post-embryonic ontogenetic series from protaspid to holaspid period based on numerous articulated specimens is clearly demonstrated and reported as a ptychopariid representative. The full post-embryonic developmental sequence, which exhibited a heteronomous trunk segment condition and an unbalanced rate in segment expression and liberation during ontogeny, witnessed a marked intraspecific variation in somitogenesis and tagmosis during the life cycle. The progressive release of the trunk segments may vary at rates among different individuals, revealing a potential developmental strategy how early diversified arthropods controlled the form of the body patterning as well as the proportion of head to trunk in size during the enrollment process of its life cycle. (c) 2025 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. All rights are reserved, including those for text and data mining, AI training, and similar technologies.