126


Journal of Paleontology 92(2):115–129


sensu stricto as close relatives of extant Nematoida. Parsimony analysis (Datamatrix 4) with large sampling including extant and extinct cycloneuralians yielded 1080 MPTs (TL=338, CI=0.55, RI=0.854). The 50% majority rule consensus tree (Fig. 9.2) resolves Palaeoscolecida sensu stricto, together with some cyclo- neuralians fromBurgess Shale-type lagerstätten, as close relatives of extant Nematoida, while E. sphinx and some other early cyclo- neuralians are resolved within crown-group Priapulida. From previous and the current analyses, it is evident that the


Han et al. (2013, 2016a, b) regarded some fossil embryos


phylogenetic position of Eopriapulites is heavily influenced by the taxa included in the analyses. Eopriapulites canberesolvedasstem- lineage derivative of Scalidophora (Liu et al., 2014b; Shao et al., 2016), stem-lineage derivative of Nematoida, or even crown-group Priapulida, thus its position is heavily unstable. Based on current knowledge of the ground pattern of Scalidophora, Nematoida, and Cycloneuralia, Eopriapulites has an uncertain position and should be assigned to total-group Cycloneuralia.


Discussion


Debate about the affinity of olivooids.—Though traditionally accepted as possible coronate scyphozoans, many other hypotheses have been proposed for Olivooides and/or Quad- rapyrgites, including the echinoderm hypothesis (Chen, 2004), cubozoan cnidarian hypothesis (Han et al., 2016a, b), stem-lineage cycloneuralian hypothesis (Steiner et al., 2014), and stem lineage of Diploblastica hypothesis (Yasui et al., 2013). The echinoderm hypothesis has been criticized by many authors (e.g., Dong et al., 2013, 2016; Liu et al., 2014a) and can be effectively rejected. The discussion here focuses on the stem-lineage cycloneuralian hypothesis in light of the oldest known cycloneuralians recovered from the Fortunian Stage in recent years, and on the cubozoan hypothesis that competeswith the scyphozoan hypothesiswithin a broader cnidarian interpretation. Bengtson and Yue (1997) originally noted the similarity


between Punctatus tubes and the loricate larvae of Priapulida. Steiner et al. (2014) compared the olivooid tubes with the pre- loricate larvae of modern priapulids. Modern pre-loricate larvae of priapulids do not feed and lack an anus, but an anus is developed immediately after the second loricate larval stage (Wennberg et al., 2009). The known material assigned to olivooids lacks an anus throughout the whole ontogeny (Yasui et al., 2013; Steiner et al., 2014). Annuli are added one by one during elongation of the tubes (Liu et al., 2014a). Based on the Zhangjiagou material (Figs. 4.5, 6.11), the adults of olivooids are estimated to have reached centimeter scale with more than 50 annuli. Accordingly, if olivooids actually represented cycloneuralians, the absence of an anus would imply growth to 50 annuli requiring at least 49 separate molts without any food intake. The physiological energetics of molting requires corresponding nutrition that does not support a non-feeding larvae hypothesis. Olivooids are interpreted here as being radially symmetric, contrasting completely with the bilateral symmetry of cycloneuralians. The oldest known cycloneuralians, exemplified by Eopriapulites and Eokinorhynchus (Zhang et al., 2015; Shao et al., 2016), along with the younger Shergoldana (Maas et al., 2007) had already developed an introvert armored with scalids. Olivooids lack not only an anus, but also the specific characteristics of cycloneuralians, such as an introvert with scalids. Therefore, the stem-lineage cycloneuralian hypothesis is not supported here.


from the Kuanchuanpu Formation at the Shizhonggou section as cubozoans. This hypothesis was based on plausible internal biological structures, such as possible tentacles, frenula, oral marginal lappets, and gastric saccule-like humps, which might be more compatible with those of modern cubomedusozoans. Among these fossil embryos belonging to species of Olivooides and Quadrapyrgites, Han et al. (2016b) recognized a series of the same internal structures of embryos of Olivooides multisulcatus and described them following the terminology of modern cubomedusozoans. This methodology implies that the embryos are direct developers, and they would hatch directly into juvenile cubomedusozoans without passing a planular phase and a polypoid phase. Following this hypothesis, the hatched stages of Olivooides and Quadrapyrgites have to be regarded as stalked medusoid stages, with the periderm embracing the internal cubomedusozoans completely. The current material from the Zhangjiagou section implies that the stalked stages are continuously developed, extending from small hatchlings with only one annulus to large individuals with ∼50 annuli. Medusoid stages in a stalked lifestyle occur only in modern staurozoans, which are interpreted as the sister group of all other Medusozoa (Miranda et al., 2016). Accordingly, the cubozoan hypothesis demands that the stalked medusoid forms occurred independently twice—once in early cubozoans, such as olivooids, and once in modern staurozoans. It also demands that the all-embracing periderm occurred independently twice— once in early cubozoans, such as olivooids, and once in modern coronate scyphozoans. This is a rather un-parsimonious evolutionary scenario for early cnidarian evolution, thus is not favored here.


Series, not long after eumetazoan origin and diversification, and earlier than the first occurrence of palaeoscolecids (Cambrian Series 2). Again, Eopriapulites andMarkuelia,with their similar and seemingly plesiomorphic morphology, have been proposed to be early scalidophorans (Shao et al., 2016) or in-group scalidophorans (Dong et al., 2010). However, the current analysis indicates that at least Eopriapulites might also be a close relative of Nematoida (Fig. 9.1). The uncertain phylogenetic assignments with


Eopriapulites as an ancestral cycloneuralian.—It has previously been proposed that the ancestral cycloneuralians were macroscopic, “priapulid-like,” introvert-bearing animals. Accordingly, macro- scopic palaeoscolecids from the Burgess Shale-type lagerstätten were proposed to represent ancestral cycloneuralians or even ancestral ecdysozoans (Budd, 2001, 2003b; Harvey et al., 2010). The palaeoscolecids range from the early Cambrian to late Silurian, ca. 520–420 Ma (Harvey et al., 2010). A potential ancestor should have occurred at least no later than other members of its lineage. But based on the current data, at least three fossil cycloneuralians have occurred earlier than the earliest palaeoscolecids: Markuelia secunda Val’kov in Val’kov and Karlova, 1984 from the Pestrotsvet For- mation of Siberia (ca. 521–525 Ma); Eopriapulites sphinx and Eokinorhynchus rarus from the lower Fortunian Stage of South China (ca. 535 Ma). The occurrence of these cycloneuralians implies that the cycloneuralians should have been rooted in the Fortunian Stage, or possibly even earlier, and that the ancestral cycloneuralian/ ecdysozoan hypothesis of palaeoscolecids is challenged. Eopriapulites and Markuelia occurred in the Terreneuvian


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