Fig. 5: Proposed homology of brain components in early panarthropods.

Phylogenetic analysis situates Youti yuanshi within the AOPK clade containing Anomalocaris, Opabinia, Pambdelurion and Kerygmachela. Under our preferred model, the circumoral brain ring of cycloneuralians corresponds to the panarthropod prosocerebrum, which innervates the first appendage pair (onychophoran antennae, tardigrade stylets or euarthropod labrum). We interpret the archicerebrum as a distinct development dorsal to the prosocerebrum, associated with sensory receptors: specifically the eyes, and the dorsal projections (Kerygmachela rostral spines, tardigrade cirri, crustacean frontal filaments or anterior paired projections of stem euarthropods; homology with the anteriormost onychophoran lip papillae is plausible, but may not be parsimonious). The taxa depicted in this figure are selected in order to depict the evolutionary context of Youti; the relationships shown are recovered under all analytical conditions.