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Old Medusozoan from the Kuanchuanpu

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Old Medusozoan from the Kuanchuanpu [Palaeontology, 2017, pp. 1–15] ANATOMY AND AFFINITIES OF A NEW 535-MILLION-YEAR-OLD MEDUSOZOAN FROM THE KUANCHUANPU FORMATION, SOUTH CHINA by XING WANG1,2 ,JIANHAN1,*, JEAN VANNIER2,QIANGOU3,4, XIAOGUANG YANG1,KENTAROUESUGI5, OSAMU SASAKI6 and TSUYOSHI KOMIYA7 1Early Life Institute & Department of Geology, State Key Laboratory of Continental Dynamics, Northwest University, 229 Taibai Road, Xi’an, 710069, China; [email protected] 2UMR 5276 du CNRS, Laboratoire de geologie de Lyon: Terre, Planetes, Environnement, Universite Lyon 1, B^atiment GEODE, 2, rue Rapha€el Dubois, Villeurbanne, 69622, France 3Early Life Evolution Laboratory, School of Earth Sciences & Resources, University of Geosciences, Beijing, 100083, China 4Department of Zoology, University of Kassel, Kassel, 34132, Germany 5Japan Synchrotron Radiation Research Institute (JASRI) 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo Japan 6Tohoku University Museum, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai, Japan 7Department of Earth Science & Astronomy, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, 153-8902, Japan *Corresponding author Typescript received 10 April 2017; accepted in revised form 30 June 2017 Abstract: We describe here Sinaster petalon gen. et sp. pockets. Although Sinaster cannot be straightforwardly nov., a new embryonic form from the c. 535 million-year- assigned to any crown-group within Medusozoa, the pres- old Kuanchuanpu Formation of South China (Ningqiang, ence of marginal lappets and endodermal lamellae suggests Shaanxi Province). The excellent three-dimensional, phos- that it is closer to Cubozoa and Scyphozoa than to any other phatic preservation of these microfossils allowed us to use group of modern cnidarians. The tentative placement of x-ray microtomographic techniques to make accurate recon- Sinaster within the stem-group Cubozoa is justified by the structions of their internal structures and to compare their presence of a velarium supported by a frenulum. The cubo- anatomy point-by-point with that of extant cnidarians and zoan affinities of Sinaster are also supported by cladistic other animal groups. Sinaster petalon has anatomical features analysis. typical of extant Medusozoa (Cnidaria), such as coronal muscles, perradial and adradial frenula, interradial septa, Key words: Cnidaria, Cubozoa, Early Cambrian, embryo, accessory septa, gonad-lamellae, tentacle buds and perradial Kuanchuanpu Formation, periderm. T HE small shelly fossil (SSF) assemblages of the Kuan- organisms (Chen & Dong 2008; Han et al. 2010, 2013, chuanpu Formation of South China (Shaanxi Province; 2016a, 2017b, c; Dong et al. 2013). Steiner et al. (2004) Fortunian Stage, Terreneuvian Series, c. 535 Ma) contain described a scyphopolyp with many filamentous tentacles, abundant skeletal elements (He 1987; Qian 1999) but also Han et al. (2010) the earliest sea-anemone-like cnidarian remarkably preserved soft-bodied organisms such as embry- and Dong et al. (2013) a possible ephyra-like medusa onic and larval stages of cnidarians (Conway Morris & Chen with pentaradial symmetry. The oldest representatives of 1992; Bengtson & Yue 1997; Steiner et al. 2004; Dong et al. Cubozoa (box jellyfish) were also discovered in the Kuan- 2013, 2016; Han et al. 2013, 2016a), ecdysozoans (Liu et al. chuanpu Formation (Han et al. 2013). The exquisite 2014; Zhang et al. 2015) and also possible meiobenthic preservation of their septal structures allowed unprece- deuterostomes (Han et al. 2017a ). These exceptional fossils dented detailed comparisons with their modern counter- provide key information on the early stages of animal evolu- parts (Han et al. 2013, 2016a, b; Toshino et al. 2015). Liu tion near the Ediacaran–Cambrian boundary and before the et al. (2014) and Zhang et al. (2015) described two min- Cambrian Explosion sensu stricto. ute scalidophoran worms, which provide insight into the Recent studies using scanning electron microscopy early evolution of ecdysozoans, a major animal clade that (SEM) and x-ray microtomography (XTM) provide very rapidly became dominant in the later Cambrian marine detailed morphological information on these early ecosystems exemplified by the Chengjiang biota. © The Authors. doi: 10.1111/pala.12320 1 Palaeontology published by John Wiley & Sons Ltd on behalf of The Palaeontological Association. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. 2 PALAEONTOLOGY Although the anatomy of many of these early cnidari- Cubomedusa and Scyphomedusa are used here to desig- ans and ecdysozoans has been reconstructed in detail, nate the medusoid stages of Cubozoa and Scyphozoa. important aspects of their palaeobiology, taphonomy, sys- tematics and phylogeny remain poorly understood or Abbreviations. aal, adradial apertural lobe; af, adradial debated, especially their cycle of development from furrow; afl, adradial fold lappet; afr, adradial frenulum; embryo to adult, their taxonomy and their phylogenetic as, accessory septum; cg, coronal groove; cl, claustrum; relationships to extant groups (Dong et al. 2013, 2016; crm, circumferential muscle; cs, coronal stomach; Han et al. 2013). Numerous forms have been kept in en + pe, egg envelope + periderm; eu, exumbrella; g, open nomenclature in order to avoid potential problems gonad; gl, gonad-lamella; go, gastric ostium; icp, interra- of synonymy until additional specimens can be obtained. dial corner pillar; if, interradial furrow; is, interradial sep- One of the most studied forms, Olivooides Qian, 1977 tum; ln, lappet node; mb, manubrium; ml, marginal (see Bengtson & Yue 1997 for a reconstructed develop- lappet; mp, mesogonial pockets; pal, perradial apertural mental cycle), is a spherical organism with an external lobe; pfl, perradial fold lappet; pfr, perradial frenulum; stellate ornament that is assumed to represent the embry- ph, phacellus; pp, perradial pocket; rc, radial canal; sf, onic stage of a larger tubular animal from the same local- septal funnel; sn, septal nodes; sp, suspensorium; stl, stel- ity that has been described as Punctatus (Bengtson & Yue late ornaments; su, subumbrella; tb, tentacular bud; ve, 1997; Yue & Bengtson 1999a, b; Yao et al. 2011, fig. 3b1). velarium; *, perradius; ?, interradius. Recent studies (Dong et al. 2013; Han et al. 2013) have also revealed that Olivooides-like fossils had a pentaradial anatomy as evidenced by the connection of the gastric MATERIAL AND METHOD septa (mesenteries) to the double-layered body wall and the arrangement of tentacles and gonad lamellae. As a Fossil specimens were obtained by acetic acid maceration whole, this body plan is comparable to that of some of phosphatic limestones from the Kuanchuanpu Forma- extant medusozoans such as cubomedusozoans (Han tion (Qian 1999) and picked under a binocular micro- et al. 2013) or scyphomedusozoans (Dong et al. 2013, scope. Two specimens (ELISN 89-107 and ELISN 115-39) 2016). The symmetry of these embryonic fossils is domi- were examined under SEM and then investigated with nantly pentamerous, but some of them are tetraradial computed x-ray microtomography (XTM) at Tohoku (Han et al. 2016b) as in the vast majority of extant University, Japan, and the synchrotron of Spring-8 in cnidarians. Although the Olivooides-like cnidarians from Hyogo, Japan. SEM and XTM (Tohoku University, Japan) the Kuanchuanpu biota are prehatched embryos with vir- were both used to image the external and internal features tually the same overall external morphology as Olivooides, of the best preserved specimens (Wang et al. 2017, appen- they display a greater variety of internal structures. We dices 1, 2). Selected specimens were further examined describe here a new genus and species, Sinaster petalon using synchrotron radiation at Spring-8 in Hyogo, Japan. gen. et sp. nov., based on exceptionally well-preserved Thousands of images of virtual thin-sections (Figs 2, 5) prehatched embryos from the Kuanchuanpu Formation. through each specimen were acquired at a resolution of Although Sinaster resembles Olivooides-like fossils in its 1004 9 1004 pixels (XTM) and 1920 9 1920 pixels (syn- overall shape, its internal structures clearly distinguish it chrotron XTM). XTM data were processed using V.G. from other co-occurring embryos. Studio 2.2 Max in order to enhance contrast between key internal anatomical features by using artificial colours and to generate detailed three-dimensional reconstructions of TERMINOLOGY AND ORIENTATION OF the microscopic fossils (Figs 3–4, 6–7). Cladistic analysis EMBRYONIC MEDUSOZOANS was carried out using PAUP* v. 4.0 b10 (Swofford 2003). The unweighted analysis of the data matrix (Wang et al. The terminology used here is that of previous works on 2017, appendix 3) containing 104 unordered characters Cambrian and extant cnidarians (Hyman 1940; Thiel taken from Marques & Collins (2004), Van Iten et al. 1966; Werner 1973; Thomas & Edwards 1990; Gershwin (2006a) and Han et al. (2016c). & Alderslade 2006; Han et al. 2013, 2016a, b). All specimens are deposited at the Early Life Institute The definition of the meridian plane in these specimens (ELI), Northwest University, Xi’an, Shaanxi Province, follows Han et al. (2013, 2016a, b). We follow the current China. This material and microtomography data are classification of Cnidaria into the Class Anthozoa and the available on
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