An exceptionally preserved euarthropod with unique feather-like appendages from the Chengjiang biota

Micro-CT scanning of the Cambrian euarthropod Chuandianella ovata reveals unprecedented three-dimensional soft-part details. It has an elongate uniramous antennule and a short uniramous second appendage, followed by ten homonomous biramous appendages, each comprising a short paddle-shaped exopod and a unique feather-like endopod with at least 27 podomeres each of which bears a long blade-like endite with a short terminal seta. Based on its carapace and previously known soft-part anatomy C. ovata was compared with the Burgess Shale mandibulate euarthropod Waptia. However, Waptia has recently been shown to bear specialized head appendages that are interpreted as a mandible and maxillula, posterior to which are four appendages each with five-segmented endopods. In contrast, we interpret Chuandianella as an 9upper9 stem-group euarthropod that possessed neither a differentiated mandible nor a maxillula. Chuandianella further demonstrates that early Cambrian 9upper9 stem-group euarthropods were experimenting with a range of different limb arrangements and morphologies.