Shao et al.—Fortunian cnidarians and cycloneuralians in South China
Scalidophora or Nematoida imply that Eopriapulites has characters that are shared with both Scalidophora and Nematoida (i.e., with the stem of Cycloneuralia). This is very similar to the younger Sher- goldana australiensis, which also has been assigned to total group Cycloneuralia. The specific character combination of the only known but exceptionally 3D-preserved specimen of this species, has both nematoid and scalidophoran characters, implying an assign- ment outside any in-group. An assignment to Nematoida or Scali- dophora can even be ruled out based on its well-known morphology (Maas et al., 2007). A new hypothesis proposed here is that Cycloneuralia might
have originated in the Fortunian small shelly faunas rather than in the early Cambrian macrobenthos, implying that the ancestral cycloneuralians should have been microscopic, vermiform, intro- vert-bearing, and have characters more like Eopriapulites sphinx. Previous studies have shown that Markuelia might be more basal than Eopriapulites (Shao et al., 2016), implying that pentaradially symmetric arrangements of introvert scalids occurred earlier than hexaradially symmetric forms. Therefore, the last common ancestor of Cycloneuralia might have possessed an introvert with internally hollow and pentaradially arranged introvert scalids. Internally hol- low and pentaradially arranged introvert scalids may have been inherited by the last common ancestor of Scalidophora and possibly also by the lineage leading to modern Nematoida, therefore might have been lost autapomorphically early in this lineage.
Conclusions
The Fortunian Zhangjiagou Lagerstätte has yielded three- dimensionally phosphatized microfossils of radiate animals and cycloneuralians. Radiate animals include embryos of Olivooides multisulcatus, Olivooides mirabilis,and Pseudooides prima,as well as putative hatched stages of O. multisulcatus, O. mirabilis, Hexaconularia sichuanensis,and Quadrapyrgites quadratacris. These radiate animals represent the diversification of cnidarians in the Fortunian Stage. Cycloneuralians are represented by Eopriapulites sphinx and trunk fragments possibly related with Eokinorhynchus rarus (Zhang et al., 2015, their unnamed forms I and II).
important information on the early diversification of cnidarians and cycloneuralians. Based on these fossils, we propose (1) cnidarians have a high diversity in the Fortunian Stage of South China, and symmetry patterns include biradial (Pseudooides and Hexaconularia), triradial (Anabarites), tetraradial (Quad- rapyrgites), and pentaradial (Olivooides and Qinscyphus Liu, Shao, and Zhang in Liu et al., 2017) symmetry; (2) P. prima might be the embryonic stage of the co-occurring H. sichua- nensis, with the biradial symmetry as a possible uniting feature; (3) the adults of Olivooides and Quadrapyrgites might have had a length exceeding 1 cm with more than 50 annuli on the post- embryonic surface, and the unusually large specimens of Oli- vooides and Quadrapyrgites can refute the non-feeding larvae hypothesis for Olivooides and Quadrapyrgites; (4) because of the lack of convincing internal soft-part anatomy, Olivooides and Quadrapyrgites might better be assigned to coronate scy- phozoans, with the all-embracing periderm as a key uniting feature; and (5) the cycloneuralians, and possibly the ecdy- sozoans or nemathelminths, might have originated in the
These exceptionally preserved microfossils provide
127
Fortunian small shelly faunas as part of the meiofauna rather than in the macrobenthos, with their ancestors being similar in morphology with Eopriapulites sphinx. As a consequence, ancestral cycloneuralians might have possessed pentaradially arranged and internally hollow introvert scalids. Such scalids may have been inherited by the last common ancestors of Sca- lidophora and Nematoida, used originally exclusively or mainly for locomotion, but were lost early in the crown-group of the Nematoida. The final important point is that Cambrian cycloneuralians
cannot all be treated simply as “priapulids” as pointed out by Maas et al. (2007) and Maas (2013) because such an assignment is not justified by any characters. Again, following Maas (2013), we emphasize that the morphology of Cambrian cycloneur- alians, including Eopriapulites sphinx, does not give any hint that Cycloneuralia is the sister taxon of Panarthropoda, as indi- cated by the Ecdysozoa hypothesis.
Acknowledgments
This work was supported by the National Natural Science Foun- dation of China (41572007, 41572009), the State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (173121), the Youth Innovation Promotion Association, Chinese Academy of Sciences (2016283), Quality Project of Chang’an University (0012-310600161000, 0012-310627171808), College Students’ Innovative Entrepreneurial Training Program of Chang’ an University (201710710062, 201710710063, 201710710240, 0012-310600161000, 0012-310627171808) and The Tenth “Challenge Cup” Competition of Chang’ an University (C-P-B-2, C-P-B-6, C-P-B-8). Two anonymous referees provided careful revisions and constructive suggestions to this paper. Jisuo Jin and Brock Glenn provided careful technical edits and language
polishing.Correspondence should be addressed toHZ(hqzhang@
nigpas.ac.cn) or YL (
stotto@163.com).
Accessibility of Supplementary Data
Data available from the Dryad Digital Repository: https://doi. org/10.5061/dryad.1cn6b
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