Liu et al.—Upper Cambrian cycloneuralians from South China


95


Figure 7. Austroscolex sinensis new species from the Furongian Bitiao Formation of Wangcun section. (1) NIGP160457; (2) holotype, NIGP160456; (3) enlargement of area in rectangle in (1); (4) enlargement of area in rectangle in (2). (1, 2) Scale bar = 500 µm; (3) scale bar = 128 µm; (4) scale bar = 59 µm.


Eopriapulites likely represents an ancestral form of cycloneur- alians. If we accept Eopriapulites as a potential ancestral cycloneuralian, the last common ancestor of the Cycloneuralia, and even of the Ecdysozoa, might have been microscopic and possessed an introvert with internally hollow scalids. This character was retained by the last common ancestor of Scalidophora and by the last common ancestor of Nematoida, but got lost secondarily in crown-group Nematoida.


Discussion


The Wangcun section is an ideal place to test the possible rela- tionship between the fossil embryo Markuelia and palaeoscolecids


because they co-occurred in the key horizon (Fig. 1.2). Markuelia was previously proposed to be a direct developer (Dong et al., 2004), but this is difficult to verify due to the lack of fossils representing the postembryonic or free-living stages (Haug et al., 2009). Huang et al. (2006) proposed that Markuelia might be a palaeoscolecid, but this was challenged by Duan et al. (2012) because of the distinct anatomies of the two taxa. For example, Markuelia fossils uniformly have three pairs of tail spines (Dong et al., 2010), whereas palaeoscolecids have only one or two pairs of tail spines (Duan et al., 2012). Palaeoscolecids are ornamented with plates, platelets, and microplates on the trunks, whereas Markuelia has few trunk ornamentations. The debate cannot be resolved with confidence because palaeoscolecids are represented


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