The Cambrian crown-group pancrustacean Sunella chimera sp. nov. with raptorial anteriormost appendages

Cambrian records of crown-group Pancrustacea have been restricted to the taphonomic windows of microfossils, including the Orsten-type material and the small carbonaceous fragments. The macrofossil form of the Cambrian crown-group Pancrustacea has not been known. Sunella chimera sp. nov., herein reported from the Cambrian Stage 3 Chengjiang biota, displays a second appendage with a gnathal element, a mandible with a gnathal edge and an anteriorly directed setose endopod, a paragnath, a maxillule and a maxilla both with enditic protopods and setose endopods, and trunk appendages with a leaf-shaped epipod and a 5-segmented endopod, features that unambiguously indicate crown-group pancrustacean affinity. Sunella exhibits a higher degree of appendage differentiation than the Orsten taxa, and its morphologies are less deviated from the prototype of Pancrustacea compared with previously reported mandibulate and pancrustacean macrofossils with evolved loss of the second appendage and cephalic exopods. Hence, it updates our knowledge on the ground body pattern of Pancrustacea, provides key insights into the origin of this diversified lineage and offers a crucial calibration point for evolutionary study. With a unique appendicular organization that incorporates both a raptorial anteriormost appendage and pancrustacean-type biramous appendages, Sunella adds to the morphological diversity of early Pancrustacea and supports the cryptic Cambrian radiation of this lineage. Appendicular organization of the Cambrian bivalved euarthropod Sunella chimera sp. nov. indicates that it is a crown-group pancrustacean with raptorial anteriormost appendages.