A THREE-DIMENSIONALLY PHOSPHATIZED SCALIDOPHORAN WORM FROM THE EARLIEST CAMBRIAN PERIOD

Scalidophorans (priapulids, loriciferans, and kinorhynchs) are ecdysozoans related to nematoids and arthropods. As such, their fossil record can inform about the evolutionary history of some of the most diverse animal phyla. Cambrian scalidophorans are common in the Chengjiang and Burgess Shale biotas, but they are often preserved as two-dimensional compressions and their three-dimensional morphological reconstruction often has to be made under the guidance of living priapulids. Markuelia is a three-dimensionally phosphatized scalidophoran from Cambrian-Ordovician rocks, but it is only known as embryo fossils and its full developmental pathway is unknown. Here we report a post-embryonic fossil of the oldest known scalidophoran from the Fortunian (early Cambrian) of South China. The new fossil preserves an introvert armed with scalids, a circlet of coronal scalids, and circlets of pharyngeal teeth. Its scalids and pharyngeal teeth are hexaradially arranged, rather than in a pentaradial pattern as in living priapulids. The new fossil is resolved as a stem-group scalidophoran and can provide important insights into the body plan evolution of early ecdysozoans.