New material of the oldest known scalidophoran animal Eopriapulites sphinx

Abstract

Eopriapulites sphinx is the oldest known scalidophoran animal and so far the only cycloneuralian body fossil from the Cambrian Fortunian Stage. The hexaradial symmetry exhibited by the arrangement of its pharyngeal teeth, coronal scalids and introvert scalids expand our knowledge on the early evolution of cycloneuralians. The holotype and only specimen is a fragment with the proboscis and the anterior trunk part preserved, but the posterior trunk part is missing. Here, we report three-dimensionally phosphatized worm trunk fragments from the same locality and horizon yielding E. sphinx. They are regarded as conspecific with E. sphinx based on co-occurrence and identical annulations, and provide key information on the trunk morphology. E. sphinx is completely reconstructed here as a long vermiform animal with densely annulated trunk and no caudal outgrowths. An updated phylogenetic analysis supports that E. sphinx is a stem-lineage derivative of Scalidophora and also indicates that the hexaradial symmetry of Eopriapulites might have evolved independently from that of Nematoida.