Cambrian euarthropod sheds light on the origin of Artiopoda body plan.

The origin and evolution of trilobated body plan of the Artiopoda, a group of epibenthic euarthropods from Cambrian Lagerstätten, remain unclear. Here we examine old and new specimens of , one of euarthropods from the Chengjiang biota, revealing new morphological details and revising its taxonomy. possesses an elongate body with a five-segmented head, a thorax with 13-15 tergites, and a three-segmented pygidium with well-defined axial region. The ventral morphology includes paired stalked eyes, one fleshy antenna pair, the following homogeneous head and thoracic appendages, each with an annular proximal-element, an articulated stenopodous branch and a lamellar flap, and the pygidial appendages solely consisting of lamellar flaps. Cladistic analyses resolved as the basal-most member of the Artiopoda, offering a hypothesis of the initial origin of trilobation in the pygidium. The new data, in conjunction with the presence of the elongated body plan across major lineages of euarthropods, suggest a convergent evolution of this trait.