The earliest-known ancestors of Recent Priapulomorpha from the Early Cambrian Chengjiang Lagerstätte

Abstract

The taxonomy of an early ancestor of Recent Priapulidae,Xiaoheiqingella peculiaris (=Yunnanpriapulus halteroformis Huang et al., 2004) from the Early Cambrian Chengjiang fossil Lagerstatte, is revised. Morphological characters comprise a pair of caudal appendages rather than a single appendage flanking the trunk end and a possible urogenital duct found inside the preanal region. An additional extremely rare fossil priapulid worm,Paratubiluchus bicaudatus gen. nov., sp. nov. is also described herein. Its diagnostic characters are: an introvert bearing 25 longitudinal rows of scalids, a distinct neck region, no annulus on the oval trunk, and a pair of caudal appendages. The proportion of body parts is similar in size to that of loricate larvae of Recent priapulids and larva-formed Palaeopriapulitidae. Taking account of the features ofXiaoheiqingella, bicaudal appendages are considered to be a synapomorphy of Priapulidae and Tubiluchidae.Paratubiluchus gen. nov. is most likely a candidate for the ancestor of the Tubiluchidae; it probably originated from a larva-formed priapulid with 25 rows of scalids, thus representing an intermediate link between the priapulids in mature-form and the priapulids with lorica.