Radiodonts, a diverse clade of early Palaeozoic stem-group euarthropods, have provided critical information for understanding the evolution of this phylum, and were important constituents of marine ecosystems. The well-known Chengjiang Lagerstätte (Cambrian Stage 3, c. 518 Ma) has yielded the highest known diversity of radiodonts of any Cambrian Konservat-Lagerstätten, and represents a crucial deposit for radiodont research. One important but generally overlooked Chengjiang radiodont taxon, previously identified as Anomalocaris sp. or Radiodont C, is herein designated as the type species of a new monotypic genus, Shucaris ankylosskelos gen. et sp. nov. based on dozens of specimens. Shucaris is distinctive for its combination of several characters, including the strong curvature of frontal appendage, presence of two pairs of endites on proximalmost claw podomere, posteriorly-inward curved endites on proximal five claw podomeres, and most strikingly the coexistence of gnathobase-like structures and oral cone. Phylogenetic analysis retrieves Shucaris as either an early diverging member of Anomalocarididae or as sister to the clade Anomalocarididae + Amplectobeluidae. Moreover, our phylogenetic analysis also supports the divergence between hurdiid and non-hurdiid radiodonts. This study not only illuminates the early diversification of radiodonts, but also contributes fresh insights into the radiodont systematics and phylogeny.

Radiodonta, Shucaris gen. nov., phylogeny, gnathobase-like structure, oral cone