Cambrian waptiid euarthropod Chuandianella from the Chengjiang biota

Chuandianella ovata, a waptiid “bivalved” arthropod occurred in strara of Cambrian Series 2 and Stage 3 (ca. 521–514.5 Ma) along the western margin of the Yangtze plate, has been reported in numerous publications, whereas many morphological features still require further investigation. Herein, based on 1459 finely preserved specimens from eight localities of the Chengjiang biota, seventeen new characteristics are described and documented, and five previously described traits are revised. In our reconstruction, the cephalon bore a pair of stalked eyes with setae along the convex margin and annuli at the basal part of the eye lobes, a median triangular sclerite, one pair of biramous antennules, and three pairs of uniramous appendages that may represent the mandibules, maxillules and maxillae, respectively. According to microtomography and fossil imaging, the thorax houses nine pairs of appendages, each identified as a quadripartite, comprising a protopodite, a reduced endopodite, flap-like setose exopodite, and annulated epipodite with numerous lamellae. This appendicular morphology provides additional evidence for the presence of exites (epipodites) in Palaeozoic arthropods. Re-examination of the trunk limbs of Cambrian euarthropods indicates that exites may be a common feature that evolved deep in arthropod phylogeny.