Yang et al.—New paleoscolecid worms from early Cambrian of South China


55


Figure 4. Idealized cuticle reconstructions of Shaaxiscolex xixiangensis n. gen. n. sp. 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).


paleoscolecid worms (e.g., Cricocosmia jinningensis Hou and Sun, 1988 and Mafangscolex sinensis Hu, 2005) together with lined burrows have been collected from the Chengjiang fauna, South China (Zhang et al., 2006; Huang et al., 2014), indicating that they acted as the producers of subhorizontal burrow systems in shallow marine substrates of the Cambrian sea. On the other hand, the hints of dorsoventral differentiation of cuticular ornamentation (different morphology and/or uneven distribu- tion of the cuticular sclerites), the presence of aboral hooks, and lateral papillae and/or projection of the trunk are inferred to indicate engagement in epifaunal excursion (e.g., Müller and Hinz-Schallreuter, 1993; Zhang and Pratt, 1996; Ivantsov and Wrona, 2004; Han et al., 2007b; Maas et al., 2007; Harvey et al., 2010). As do most macroscopic compressions, paleoscolecids and


their line burrows occur invariably parallel to bedding surfaces, providing limited clue as to the original modes of life. Integral to the lifestyle, a unique individual of Shaanxiscolex xixiangensis n. gen. n. sp. obtained by splitting the longitudinal section of the rock slab, in our opinion, provides vital clues to reconstruct its


living habit, combining both vertical and horizontal spacing: the body extends obliquely to the layers of substrate at a depth of approximate 5mm, with its posterior strongly recurved (Fig. 5.1–5.3). Considering bioturbations are very common at the horizons yielding the worms (Chen and Zhang, 1987; Zhu, 2010), this fossil probably records the animal either in the process of escaping or during normal burrowing activity, captured by a depositional event. Such a burial attitude, together with the evidence that widespread, large sized, and ecologically dominanct endobenthic paleoscolecids were found living with elongate burrows (e.g., Zhang et al., 2006; Huang et al., 2014), would strongly suggest that paleoscolecids were infaunal colonizers that contributed to subvertical and oblique explora- tion of the early Cambrian substrate.


Trophic relationships.—A slender, straight digestive tract running the length of the body is essentially a conservative organization of the paleoscolecids (Conway Morris, 1997; Harvey et al., 2010), which, along with the spiny introvert, largely reflects the feeding types and strategies of the animals


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