Zhang et al.—Cambrian Fortunian scalidophoran worms in South China
the characters referring to ‘priapulid-like’ are simply those that are caracteristic for Scalidophora. Thus, E. sphinx was assigned to the stem lineage of Scalidophora (Liu et al., 2014; Shao et al., 2016). However, these stem-lineage positions might reflect the so-called ‘systematic limbo,’ indicating nothing but an uncertain position within the so-called total group (Donoghue and Purnell, 2009). Therefore, we propose that Forms A, C, and D should be assigned to total-group Scalidophora to indicate their uncertain positions within the taxon Scalidophora, as long as no more informative features supporting a further assignment are observed. A further phylogenetic analysis including at least Forms A and C must therefore await the recovery of completely preserved specimens. Form B was previously considered as scleritomes of
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found some fossils that also might be affiliated directly with early scalidophorans. Animals belonging to the stem lineage of Scalidophora, a taxon within the Cycloneuralia, molt regularly (Aguinaldo et al., 1997), and the exuviae of these early scali- dophorans can be preserved as fossils. Specimen NIGP160444 (Fig. 7.3) is preserved in a strongly distorted status, possibly being an example of an exuvia. The large spinose sclerites and the small spines are much distorted and, therefore, cannot be observed clearly. Thus, it remains somewhat uncertain whether this specimen belongs to E. rarus or to Form B. More specimens (Fig. 7.4–7.6) are recovered from the Xinli section that might represent the exuviae of early scalidophorans or co-occurring cycloneuralians. Specimen NIGP160445 (Fig. 7.4) has soft cuticle that bears annulus-like structures, whereas NIGP160446 (Fig. 7.5) is devoid of annuli but has grain-shaped cuticular textures (Fig. 7.6).
Discussion
The armor of the early scalidophoran animals sheds also light on the affinity of other coeval small shelly fossils. Zhang et al. (2015) noticed that the large spinose sclerites on Eokinorhynchus rarus and their unnamed form I are similar to disassociated small shelly fossils described as Paracarinachites spinus (Yu, 1984) (Conway Morris and Chen, 1991), different from the type material of P. spinus (Yu, 1984; Qian and Bengtson, 1989), and the small plates of their unnamed form II resemble the form Kaiyangites novoli Qian and Yin, 1984
unknown affinities or small shelly fossils. The recovery of the completely preserved specimens of Eokinorhynchus rarus sheds new light on the affinity of Form B. In fact, the small plates of Form B are densely sutured in rows (Fig. 5.1, 5.4) that resemble the arrangement of the small plates of E. rarus. Sclerites assigned to Form Bare large and spinose, similar in morphology to the large spinose sclerites of E. rarus (Fig. 3). The large spinose sclerites of Form B may have loosely covered four annuli (Fig. 5.4), and those of E. rarus cover two or at most three annuli (Zhang et al., 2015). The key difference between Form B and E. rarus is that the small plates are rectangular, lacking spines in the latter species, but long and elliptical, bearing spines, in the former. Therefore, Form B represents a scalido- phoran animal that might have close affinities with E. rarus but apparently represents a different species. Besides the five forms described in the preceding, we
(Yao et al., 2005). Therefore, Zhang et al. (2015) proposed that these disassociated small shelly fossils represented by P. spinus and K. novoli might belong to Eokinorhynchus-like scalido- phoran animals. In our materials, some disassociated small shelly fossils were also recovered from the Xinli section, with some (Fig. 7.7, 7.8) similar to the large spinose sclerites of Eokinorhynchus rarus, Form A, and Form B, some (Fig. 7.9, 7.10) similar to the small plates of Zhang and colleagues’ (2015) unnamed form II, and some (Fig. 7.11) similar to the small spines on the trunk of E. rarus, but sclerites belonging to P. spinus and K. novoli were not recovered. Despite the mor- phological similarities between these small shelly fossils and the armor on the scalidophoran animals, convergent evolution is still possible. For example, the large spinose sclerites occur on the trunk of E. rarus and Form B (i.e., some derived scalido- phoran animals within Kinorhyncha) and on the trunk of Form A and Form C. Evidently, E. rarus and Form A should be dif- ferent types of scalidophoran worms due to their very different annulation types. Thus, the large spinose sclerites may represent a convergently developed type of armor between lineages of distant affinities. This could also hold true for the remaining co-occurring small shelly fossils (Fig. 7.9–7.11). These dis- associated small shelly fossils might come from the same sca- lidophoran animals or come from different scalidophoran animals, and their exact affinity within Scalidophora remains currently unknown. An assignment more precise than being part of the taxon Scalidophora can, therefore, not be made for any of the taxa presented herein. An introvert with scalids/hooks is interpreted as an autapomorphy of either Scalidophora (Lemburg, 1995) or Cycloneuralia (Nielsen, 2012). Referring to this ‘Introverta’ hypothesis (Cycloneuralia = Introverta), the assignment must even be coarser.
Conclusions
We report scalidophoran animals from the Cambrian Fortunian Xinli section in northern Sichuan Province, South China. The specimens are fossilized in Orsten-type preservation (i.e., three- dimensionally phosphatized and soft-bodied). They can be grouped into five forms, including one form assignable to the species Eokinorhynchus rarus and four forms named in open taxonomy (i.e., Forms A, B, C, and D). E. rarus is worm-like and the body can be divided into three parts: an anterior region with introvert, a neck region, and the trunk. The trunk comprises a number of annuli that are armored with densely sutured rec- tangular plates and randomly distributed small spinose sclerites. FormAis interpreted to represent a new species. It has a densely annulated trunk with a large number of
annuli.At least five large spinose sclerites are aligned in a longitudinal row on the dorsal side. Form B is represented only by trunk fragments, but it is evidently different from E. rarus and all other coeval scalido- phoran animals in that it bears large spinose sclerites as well as trunk annuli armored with densely sutured spinose small plates that protrude into spines distally. Form C is similar in trunk morphology with Eopriapulites sphinx, i.e., with a large number of densely spaced annuli without any other ornament or struc- ture. Form D is the trunk fragment of an unknown worm-like organism. Its densely annulated trunk has a large number of annuli and a single large spinose sclerite. Forms A, C, and D are
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