The Cambrian palaeoscolecidWronascolexfrom the Shipai fauna (Cambrian Series 2, Stage 4) of the Three Gorges area, South China

Abstract

Our understanding of fossil priapulids, and in particular the palaeoscolecids, is limited owing to the rarity of preserved anterior introverts and a general absence of detailed cuticular ornament preservation in compression material. Here we describe Wronascolex yichangensis sp. nov. (Cycloneuralia, Palaeoscolecida) on the basis of overall external morphology and distinctive scleritome organization in new compressed material from the Shipai fauna, Cambrian Series 2, Stage 4 in the Three Gorges area of South China. Recurrent fine‐scale features observed in SEM analysis distinguish W. yichangensis sp. nov. from other species by its extremely closely spaced annulations, each with two rows of Hadimopanella‐type plates ranging from 37 to 62 μm in diameter but without platelets or microplates, and each plate adorned with a single circle of four to seven nodes and an occasional central node on the upper surface. Since the recent reassignment of some species from Palaeoscolex into Wronascolex, the latter genus has become a fairly diverse and cosmopolitan genus ranging from Cambrian Stage 4 to Drumian in age. However, knowledge of the sclerite pattern of Wronascolex and its associated microstructure for taxonomic purposes are still poorly understood. Since the origins of the phosphatized Hadimopanella‐type sclerites are apparently quite diverse, evaluating the biodiversity and biostratigraphic utility of Wronascolex is currently problematic.

New paleoscolecid worms from the early Cambrian north margin of the Yangtze Platform, South China

“…Whereas the occurrence of the trilobite Palaeolenus in the lower Yanwangbian Formation (e.g., Cheng et al, 1980; Chen and Zhang, 1987) indicates that the fossil horizons are generally correlated with the Canglangpuan regional stage for South China (Zhang et al, 2008) and Series 2, Stage 4 of the provisional stratigraphic scheme for the Cambrian (Peng et al, 2012). It is therefore coeval with the Shipai fauna (Zhang and Hua, 2005; Yang and Zhang, 2016) and the Guanshan biota (Luo et al, 2006; Hu et al, 2008), also from South China, as well as the Emu Bay Shale from South Australia (Paterson et al, 2008). Clearly then, the Yanwangbian assemblage is a new Burgess Shale–type biota, implying a unique faunal realm from the north margin of the Yangtze Platform during the early Cambrian.…”

“…Since macroscopic and compressed paleoscolecids collected from shales often superficially resemble one another in gross morphology (Conway Morris, 1997; Harvey et al, 2010; Yang and Zhang, 2016), the rare preservation of their cuticular ornamentations prevents straightforward comparisons with Shaanxiscolex xixiangensis n. gen. n. sp. However, the arrangement of scleritomes of S. xixiangensis is reminiscent of some previously reported paleoscolecid taxa (Fig.…”

“…and other related taxa. ( 1 ) Shaaxiscolex xixiangensis ; ( 2 ) Wronascolex yichangensis Yang and Zhang, 2016 from the Shipai Biota (Cambrian, Stage 4), South China (after Yang and Zhang, 2016); ( 3 ) Guanduscolex minor Hu et al, 2008 from the Guanshan Biota (Cambrian, Stage 4), South China (after Hu et al, 2008); ( 4 ) Paleoscolecid (SAMP 43301) under open nomenclature from the lower Cambrian Mernmerna Formation of South Australia (after Topper et al, 2010). …”

“…Many researchers, however, have suggested that paleoscolecids shared classical morphology and developmental biology with stem priapulids (Conway Morris, 1997; Huang, 2005; Han et al, 2007b; Hu et al, 2012; Wills et al, 2012), but not with panarthropods (Harvey et al, 2010), although a more robust analysis of their affinities is required for assessing the significance for ecdysozoan evolution. Furthermore, since incomplete diagnoses and undetected synonymies are common in this group, considerable problems arise in many cases when comparisons are made among morphological characters of fossils preserved in different styles and of variable quality (Conway Morris and Peel, 2010; Harvey et al, 2010; Topper et al, 2010; García-Bellido et al, 2013; Yang and Zhang, 2016).…”

“…The fossil records of compressed paleoscolecids preserving an armored terminal introvert from several Cambrian deposits (e.g., Hou and Bergström, 1994; Chen, 2004; Hou et al, 2004; Huang, 2005; Han et al, 2007b; Maas et al, 2007; Dornbos and Chen, 2008; Conway Morris and Peel, 2010; Hu et al, 2012; García-Bellido et al, 2013; Yang and Zhang, 2016) provide opportunities to constrain their taxonomies and precise affinities. Except for the frontal introvert, however, cuticle ornamentation (e.g., plates, platelets, and microplates) in compression paleoscolecids, which are the key characteristics in taxonomic purposes of the group (Conway Morris, 1997; Botting et al, 2012), are unfortunately poorly preserved.…”