The early Cambrian Bushizheia yangi and head segmentation in upper stem-group euarthropods

Bushizheia yangi O'Flynn & Liu, a euarthropod from the lower Cambrian (Series 2, Stage 3) Chengjiang Konservat-Lagerst & auml;tte, possesses both raptorial frontal appendages sharing traits with stem-group euarthropods, and deuteropodan characters shared by all extant euarthropods (e.g. dorsal arthrodization and arthropodization of all limbs). Microtomography of new specimens of B. yangi shows previously unknown details of head morphology: a six-segmented head composed of an ocular segment that carries diminutive paired stalked eyes, a post-ocular segment with deutocerebral frontal appendages, and four subsequent cephalic segments each bearing a pair of appendages. The phylogenetic position of B. yangi in the euarthropod stem-group adds support to a six-segmented head being an ancestral state for Deuteropoda. This study also reports the first occurrence of possible eggs closely associated with B. yangi. The homology of raptorial frontal appendages between lower stem-group euarthropod radiodonts and deuteropods (i.e. upper stem and crown-group euarthropods) is strengthened by similarity and phylogenetic continuity between B. yangi, its likely sister taxon Kiisortoqia soperi Stein, from the Sirius Passet Konservat-Lagerst & auml;tte, and other euarthropod taxa.