Body wall homologies in basal blastozoans

S. Zamora & I. Rábano (eds.), Progress in Echinoderm Palaeobiology. Cuadernos del Museo Geominero, 19. Instituto Geológico y Minero de España, Madrid. ISBN: 978-84-7840-961-7 © Instituto Geológico y Minero de España 2015 BODY WALL HOMOLOGIES IN BASAL BLASTOZOANS Bertrand Lefebvre1, Elise Nardin2 and Oldrich Fatka3 1 UMR CNRS 5276 LGLTPE, Université Lyon 1, 2 rue Raphaël Dubois, 69622 Villeurbanne cedex, France. [email protected] 2 UMR CNRS-IRD-UPS 5563 Géosciences Environnement Toulouse, Observatoire Midi-Pyrénées, 14 avenue Edouard Belin, 31400 Toulouse, France. [email protected] 3 Charles University, Institute of Geology and Palaeontology, Albertov 6, 128 43 Prague 2, Czech Republic. [email protected] Keywords: Cambrian, Blastozoa, Extraxial-Axial Theory, Echinodermata, Homology. INTRODUCTION When echinoderms first appeared in the fossil record in Cambrian Series 2, they were already diverse and widespread (Smith et al., 2013; Zamora et al., 2013a). The initial stages of their diversification are relatively well documented in both Laurentia and Gondwana (Lefebvre and Fatka, 2003; Smith et al., 2013; Zamora et al., 2013a). These two regions have yielded assemblages consisting exclusively of radially symmetrical forms: blastozoans (gogiid eocrinoids and lepidocystids), edrioasteroids and helicoplacoids. The later appearance (Cambrian Series 2 - 3 boundary) of echinoderm taxa with asymmetrical, flattened body plans (cinctans, ctenocystoids, solutans, stylophorans) coincides with a major ecological turnover (Dornbos, 2006). Finally, representatives of the five extant classes of echinoderms are not documented before the Ordovician (Paul and Smith, 1984; Guensburg and Sprinkle, 2001; Lefebvre et al., 2013). In Cambrian Series 2 and 3, the extremely wide morphological disparity exhibited by the earliest echinoderms is puzzling (e.g., spiral, pentaradiate, bilateral, asymmetric body outlines). This initial disparity can result either from a long unrecorded evolution, or from an extremely rapid diversification into highly specialised ecological niches (Ubaghs, 1975; Lefebvre and Fatka, 2003; Smith et al., 2013). Whatever its origin, the wide original disparity of the oldest echinoderms makes it particularly difficult to identify overarching homologies in all Cambrian taxa and thus, to elucidate their evolutionary relationships. In most recent phylogenies including basal echinoderms, character coding is largely dependent on theoretical assumptions and much emphasis is placed on the symmetry of body outlines (Smith, 2005, 2008; Zamora et al., 2012; Smith and Zamora, 2013; Zamora and Rahman, 2014). Non-radiate taxa are considered as necessarily primitive and forced down the trees, simply because of the choice of bilaterally symmetrical outgroups (e.g., hemichordates). The elaboration of a formal, robust cladistic analysis of early echinoderms urgently requires the identification of a set of objective characters based on well-defined homologies. In this context, the aim of this paper is to identify and discuss body wall homologies in the earliest blastozoans, based on both the now widely accepted extraxial-axial theory (EAT) and the report of a new “transitional” form from the Jince Formation (Cambrian Series 3) of Bohemia, Czech Republic. 87 Bertrand Lefebvre, Elise Nardin and Oldrich Fatka THE EXTRAXIAL - AXIAL THEORY The extraxial-axial theory (EAT) is a model providing keys to identify body wall homologies in both extant and extinct echinoderms. This model was initially defined mostly on ontogenetic and architectural criteria (Mooi et al., 1994; Mooi and David, 1998). In recent years, the validity of the EAT -at least in the five extant classes of echinodermswas confirmed by both embryologic data (David and Mooi, 1996, 1998) and Hox cluster analyses (Mooi et al., 2005; Mooi and David, 2008; David and Mooi, 2014). The EAT is now almost universally acknowledged as a robust framework for skeletal homologies in echinoderms (Peterson et al., 2000; Sprinkle and Guensburg, 2001; Hotchkiss, 2012; Sumrall and Waters, 2012; Smith and Zamora, 2013). The EAT identifies two main regions in the body wall of echinoderms: the axial and extraxial regions. In ontogeny, the axial region (AR) of the body wall derives exclusively from the larval rudiment. It is associated with the mouth and the water vascular system. The extraxial part of the body derives from the non-rudiment part of the larva. It forms the rest of the body wall, and can be subdivided into two parts: (1) the perforate extraxial region (PER), which contains several primary body openings (anus, gonopore, hydropore); and (2) the imperforate extraxial region (IER), without any primary opening. In primitive echinoderms, new extraxial elements can be added almost anywhere during growth. In recent years, a well-defined set of skeletal homologies (Universal Elemental Homology, UEH) was defined for individual plates associated with the peristomial border in derived blastozoans (Sumrall and Waters, 2012). The UEH model is largely based on axial elements and certainly provides a powerful tool to identify individual plate homologies within closely related taxa. Similar models of individual plate homologies have been proposed in other groups of Palaeozoic echinoderms. For example, homologies of individual skeletal elements of the PER were thoroughly investigated in stylophorans (Lefebvre and Vizcaïno, 1999). The identification of homologous individual skeletal elements is pivotal for inferring phylogenetic relationships among closely related taxa. However, this identification largely depends upon similarities of positions. Consequently, it cannot provide a robust framework for the comparison of the morphologically extremely diverse plate patterns of early echinoderms. LEPIDOCYSTIDS Lepidocystids (or imbricate blastozoans) are almost universally considered as basal-most blastozoans (Sprinkle, 1973; Ubaghs, 1975; Broadhead, 1982; Paul and Smith, 1984; David et al., 2000; Zamora and Smith, 2011). Lepidocystids have been documented in Cambrian Series 2 and 3 of Laurentia (Kinzercystis, Lepidocystis; Durham, 1968; Sprinkle, 1973; Paul and Smith, 1984), European peri-Gondwana (Vyscystis; Fatka and Kordule, 1990) and West Gondwana (unnamed form from Morocco; Smith et al., 2013). All lepidocystids share the same basic organisation, consisting in a flat to slightly domed oral surface, and an elongate cone-shaped aboral region (Fig. 1A; Sprinkle, 1973; Ubaghs, 1975; Paul and Smith, 1984). The oral surface of lepidocystids contains all main body orifices (anus, gonopore, hydropore and mouth), as well as the ambulacra (flooring plates and associated sheets of cover plates). Ambulacra regularly branch into free, erect portions (brachioles), which can be either straight (Kinzercystis, Lepidocystis) or coiled (Vyscystis). Polyplated interambulacral areas consist in numerous, tessellate plates bearing epispires. The aboral part of the body is entirely made of small, scale-like, imbricate plates. In both Kinzercystis and Vyscystis, the aboral region is relatively large and cone-shaped. In Lepidocystis, it is differentiated into (1) a short, expanded proximal part forming the cup-like, aboral portion of the bud-shaped test; and (2) a long, almost cylindrical, polyplated, distal stalk-like appendage. The morphology of lepidocystids can be readily interpreted using the EAT framework of body wall homologies (Fig. 2A). The oral surface of lepidocystids contains both the axial (cover plates, flooring plates, mouth) and perforate extraxial (interambulacral plates, anus, gonopore, hydropore and epispires) regions. The imbricate aboral sac, which contains neither any body orifice, nor any ambulacral element, can be identified as the IER of the body wall. The body plan of lepidocystids is indeed very close to that of other basal, pentaradial echinoderms (e.g., Camptostroma, Stromatocystites). The main difference with Cambrian edrioasteroid-like taxa consists in the presence of brachioles (apomorphy of blastozoans) in lepidocystids (Sprinkle, 1973; Ubaghs, 1975; Paul and Smith, 1984; David et al., 2000; Nardin et al., 2009a). 88 BODY WALL HOMOLOGIES IN BASAL BLASTOZOANS Figure 1. Basal blastozoans (latex casts of original specimens). A. Kinzercystis durhami Sprinkle, 1973, Kinzers Formation, Pennsylvania (holotype, MCZ 581). B. Undescribed transitional form between lepidocystids and gogiids, nov. gen., nov. sp., Jince Formation, Czech Republic (SZ 349). C. Gogia palmeri Sprinkle, 1973, Spence Shale, Langston Formation, Idaho (holotype, USNM 165418). Repositories: MCZ, Museum of Comparative Zoology, Harvard University; SZ: Narodni Museum, Prague; USNM: U.S. National Museum, Washington. GOGIID EOCRINOIDS Gogiids are universally considered as the most primitive representatives of the class Eocrinoidea (Sprinkle, 1973; Broadhead, 1982; Zamora and Smith, 2011). Eocrinoids are a paraphyletic assemblage uniting non-imbricate, basal blastozoans (Ubaghs, 1975; Smith, 1984; Paul, 1988; David et al., 2000; Nardin et al., 2009a; Zamora and Smith, 2011). The stratigraphic range of gogiid eocrinoids is restricted to the Cambrian Series 2 and 3 (Zamora et al., 2013a) of Laurentia (e.g., Gogia; Ubaghs, 1968, 1975; Sprinkle, 1973; Nardin et al., 2009b), European peri-Gondwana (e.g., Acanthocystites, Akadocrinus, Alanisicystis, Luhocrinus; Prokop, 1962; Fatka and Kordule, 1984, 1990; Prokop and Fatka, 1985; Ubaghs and Vizcaïno, 1990), West Gondwana (Alanisicystis; Smith et al., 2013) and South China (e.g., Balangicystis, Guizhoueocrinus, Sinoeocrinus; Zhao et al., 1994; Parsley and Zhao, 2006). The globular test of gogiids is entirely made of numerous, irregularly arranged tessellate plates (Fig. 1C). In most taxa (e.g., Alanisicystis, Gogia, Sinoeocrinus), ambulacra are short and restricted to the upper-most region of the test. Each ambulacral ray typically leads to a small group of free, erect brachioles occurring on the summit of a small, spoutlike projection (e.g., Gogia parsleyi, Sinoeocrinus). In gogiids, brachioles can be either straight (e.g., Akadocrinus, Gogia palmeri) or spirally coiled (e.g., Gogia spiralis, Guizhoueocrinus). The location of the anal pyramid, although variable, frequently occurs in lateral position on the test. The other main body orifices have been seldom documented in eocrinoids (e.g., hydropore in Alanisicystis; Ubaghs and Vizcaïno, 1990). Epispires can occur all over the test (e.g., Alanisicystis, Gogia spiralis), or they can be restricted to its upper half (e.g., Gogia kitchnerensis). However, the description of ontogenetic sequences in several gogiids suggests that the extension of epispires over the test is indeed variable during growth (Parsley and Zhao, 2006; Parsley, 2012; Zamora et al., 2013b; Nohejlová and Fatka, 2014). In most gogiids, the boundary between the test and the aboral appendage is relatively sharp. The morphology of the 89 Bertrand Lefebvre, Elise Nardin and Oldrich Fatka appendage is variable. In some taxa, it corresponds to a short, inflated, polyplated aboral sac (e.g., Alanisicystis). In most taxa, the appendage is a narrow, cylindrical, stem-like structure (stalk) made of numerous, irregularly arranged plates (e.g., Balangicystis, Gogia longidactylus). In Akadocrinus, the aboral appendage corresponds to a holomeric stem, made of homeomorphic columnals (Prokop, 1962; Sprinkle, 1973; Fatka and Kordule, 1991). The test of gogiids contains various structures indicating both axial (embedded parts of ambulacra) and perforate extraxial (e.g., anus) affinities (Fig. 2C; Mooi and David, 2008; Nardin et al., 2009a; Smith and Zamora 2013). This interpretation is supported by the extension of epispires all over the test in some taxa, and by the variable location of the anus. The aboral, stalk-like appendage of gogiids contains neither any primary body opening, nor elements associated with the water-vascular system. Consequently, this region is probably made of imperforate extraxial skeletal elements. If these identifications are correct, then (1) the flat to slightly domed oral surface of lepidocystids is homologous to the entire test of gogiids; and (2) the imbricate aboral sac of lepidocystids is equivalent to the stalklike appendage of gogiids. This implies that the tests of lepidocystids and gogiids are not homologous structures. INTERMEDIATE, SEMI-IMBRICATE BLASTOZOANS The Jince Formation (Cambrian Series 3, Drumian) of Bohemia (Czech Republic) yielded recently several exquisitely preserved specimens of basal blastozoans displaying a unique body plan organisation. Their globular, elongate test shows two clearly distinct regions (Fig. 1B). The upper two-thirds of the test are entirely made of numerous, adjacent plates bearing sutural epispires. At least two main body orifices (mouth and anus) occur in this region. Brachioles and ambulacral rays are mounted on a narrow spout-like oral surface. The presence of brachioles supports the identification of these fossils as blastozoans. The lower third of the test is entirely made of imbricate skeletal elements, without any epispire or any other body orifice. The aboral, imbricate part of the test is in physical continuity with the underlying, elongate, polyplated, imbricate stalk-like appendage. The unique body plan of the new blastozoan from the Jince Formation can be interpreted with the EAT (Fig. 2B). The upper (adoral) part of its test contains structures typical of both the AR (ambulacra, mouth) and the PER (anus, epispires). The lower (aboral) part of the test and the stalk-like appendage, which contain no main body orifice and no ambulacral (axial) elements, are both probably made of imperforate extraxial plates. If these identifications are correct, the aboral, imbricate portions of the new blastozoan (i.e., lower third of the test and stalk-like appendage) can be considered as homologous to both the elongate, aboral sac of lepidocystids and the stalk-like appendage of gogiids. The upper two-thirds of the test of the new form are thus equivalent to both the oral surface of lepidocystids and to the whole test of gogiids. Consequently, the morphology of the new Jince blastozoan appears in many respects as intermediate, transitional between lepidocystid and gogiid body plans. This new fossil strongly supports the view that the globose test of gogiids results from the complete devagination of the flat to slightly domed oral surface of lepidocystids. It also suggests that, correlatively, the contribution of the IER is dramatically reduced in gogiids (stalklike appendage) compared to the situation in lepidocystids (lateral walls of the test and aboral stalk). CONCLUSIONS The EAT provides a powerful tool to investigate body wall homologies in Early Palaeozoic echinoderms. The EAT indicates that the tests of lepidocystids and gogiid eocrinoids are not homologous, and should be assigned different names. Following Nardin et al. (2009a), the term “calyx” is proposed here for body capsules comprising a flat to slightly domed oral surface (or tegmen) and a large, cone-shaped aboral cup. The possession of a calyx possibly represents the plesiomorphic condition in early echinoderms, as it occurs in both basal edrioasteroid-like taxa (e.g., Camptostroma, Stromatocystites) and in basal blastozoans (lepidocystids). Following Nardin et al. (2009a), the term “theca” is proposed here for body capsules corresponding to fully devaginated tegmens. The possession of a theca is an apomorphy of non-imbricate blastozoans (gogiids and all more derived blastozoan taxa; David et al., 2000; Nardin et al., 2009a). The new Jince blastozoan represents a transitional form between lepidocystids and more derived blastozoans. This interpretation is based on its unique, intermediate body organisation, resulting from the partial devagination of the oral surface. The test of the Jince blastozoan cannot be identified as a calyx, because of the devagination of the tegmen, which constitutes not only the roof, but also a significant portion of the lateral body walls. However, the test of the Jince blastozoan cannot be identified as a theca, because contrary to the situation in gogiids, 90 BODY WALL HOMOLOGIES IN BASAL BLASTOZOANS Figure 2. Progressive devagination of oral surface in basal blastozoans. A. Lepidocystis wanneri Foerste, 1938, Kinzers Formation, Pennsylvania (reconstruction modified from Durham, 1968). B. Undescribed transitional form between lepidocystids and gogiids, nov. gen., nov. sp., Jince Formation, Czech Republic (camera-lucida drawing of specimen SZ 349). C. Gogia spiralis Robison, 1965, Wheeler Shale and Marjum Formation, Utah (reconstruction modified from Robison, 1965). Repository: SZ: Narodni Museum, Prague. Abbreviations: AR, Axial Region; PER: Perforate Extraxial Region; IER: Imperforate Extraxial Region. the devagination of the tegmen is only partial, and the aboral cup still contributes to a large part of the test. Consequently, the term “prototheca” is coined here, to describe tests characterised by a partial devagination of the tegmen and thus, intermediate in morphology between a calyx and a theca. Acknowledgements This paper is a contribution of the ANR (Agence Nationale de la Recherche) research project entitled “The Rise of Animal Life (Cambrian-Ordovician): organisation and tempo” (RALI, coord. Jean Vannier). The authors are particularly grateful to Samuel Zamora, who suggested important improvements to the final manuscript, and to Jim Sprinkle, for precious information on the morphology of lepidocystids. REFERENCES Broadhead, T.W. 1982. Reappraisal of class Eocrinoidea (Echinodermata). In Lawrence J.M. (Ed.), Echinoderms: Proceedings of the International Conference, Tampa Bay. Balkema, Rotterdam, 125-131. David, B. and Mooi, R. 1996. Embryology supports a new theory of skeletal homologies for the phylum Echinodermata. ComptesRendus de l’Académie des Sciences, Paris, Sciences de la vie, 319, 577-584. David, B. and Mooi, R. 1998. Major events in the evolution of echinoderms viewed by the light of embryology. In Mooi R. and Telford M. (Eds.), Echinoderms: San Francisco. Balkema, Rotterdam, 21-28. David, B. and Mooi, R. 2014. How Hox genes can shed light on the place of echinoderms among the deuterostomes. EvoDevo, 5, 22. David, B., Lefebvre, B., Mooi, R. and Parsley, R. 2000. Are homalozoans echinoderms? An answer from the extraxial-axial theory. Paleobiology, 26, 529-555. 91 Bertrand Lefebvre, Elise Nardin and Oldrich Fatka Dornbos, S.Q. 2006. Evolutionary palaeoecology of early epifaunal echinoderms: response to increasing bioturbation levels during the Cambrian radiation. Palaeogeography, Palaeoclimatology, Palaeoecology, 237, 225-239. Durham, J.W. 1968. Lepidocystoids. In Moore R.C. (Ed.), Treatise on Invertebrate Paleontology, Part S: Echinodermata 1(2). Geological Society of America and the University of Kansas Press, Lawrence, S631-S634. Fatka, O. and Kordule, V. 1984. Acanthocystites Barrande, 1887 (Eocrinoidea) from the Jince Formation (Middle Cambrian) of the Barrandian area. Věstník Ústředního ústavu geologického, 59, 299-302. Fatka, O. and Kordule, V. 1990. Vyscystis ubaghsi gen. et sp. nov., imbricate eocrinoid from Czechoslovakia (Echinodermata, Middle Cambrian). Věstník Ústředního ústavu geologického, 65, 315-320. Fatka, O. and Kordule, V. 1991. Akadocrinus knizeki sp. nov., gogiid eocrinoid from Czechoslovakia (Echinodermata, Middle Cambrian). Věstník Ústředního ústavu geologického, 66, 239-243. Foerste, A.F. 1938. Echinodermata. In Resser C.E. and Howell B.F. (Eds.), Lower Cambrian Olenellus zone of the Appalachians. Bulletins of the Geological Society of America, 49, 212-213. Guensburg, T.E. and Sprinkle, J. 2001. Ecologic radiation of Cambro-Ordovician echinoderms. In Zhuravlev A.Y. and Riding R. (Eds.), The Ecology of the Cambrian Radiation. Columbia University Press, New York, 428-444. Hotchkiss, F.H.C. 2012. Growth zones and extraxial-axial homologies in Asteroidea (Echinodermata). Proceedings of the Biological Society of Washington, 125, 106-121. Lefebvre, B. and Fatka, O. 2003. Palaeogeographical and palaeoecological aspects of the Cambro-Ordovician radiation of echinoderms in Gondwanan Africa and peri-Gondwanan Europe. Palaeogeography, Palaeoclimatology, Palaeoecology, 195, 73-97. Lefebvre, B. and Vizcaïno, D. 1999. New Ordovician cornutes (Echinodermata, Stylophora) from Montagne Noire and Brittany (France) and a revision of the Order Cornuta Jaekel 1901. Geobios, 32, 421-458. Lefebvre., B., Sumrall, C.D., Shroat-Lewis, R.A., Reich, M., Webster, G.D., Hunter, A.W., Nardin, E., Rozhnov, S.V., Guensburg, T.E., Touzeau, A., Noailles, F. and Sprinkle, J. 2013. Palaeobiogeography of Ordovician echinoderms. In Harper D.A.T. and Servais T. (Eds.), Early Palaeozoic Biogeography and Palaeogeography. Geological Society, London, Memoirs, 38, 173-198. Mooi, R. and David, B. 1998. Evolution within a bizarre phylum: homologies of the first echinoderms. American Zoologist, 38, 965-974. Mooi, R. and David, B. 2008. Radial symmetry, the anterior/posterior axis, and echinoderm Hox genes. Annual Review of Ecology, Evolution, and Systematics, 39, 43-62. Mooi, R., David, B. and Marchand, D. 1994. Echinoderm skeletal homologies: classical morphology meets modern phylogenetics. In David B., Guille, A., Féral J.P. and Roux M. (Eds.), Echinoderms through Time. Balkema, Rotterdam, 87-95. Mooi, R., David, B. and Wray, G.A. 2005. Arrays in rays: terminal addition in echinoderms and its correlation with gene expression. Evolution and Development, 7, 542-555. Nardin, E., Lefebvre, B., David, B. and Mooi, R. 2009a. La radiation des échinodermes au Paléozoïque inférieur, l’exemple des blastozoaires. Comptes-Rendus Palevol, 8, 179-188. Nardin, E., Almazán-Vásquez, E. and Buitrón-Sánchez, B.E. 2009b. First report of Gogia (Eocrinoidea, Echinodermata) from the EarlyMiddle Cambrian of Sonora (Mexico), with biostratigraphical and palaeoecological comments. Geobios, 42, 233-242. Nohejlová, M. and Fatka, O. 2014. Ontogenetic development of the genus Akadocrinus (Eocrinoidea, Echinodermata) from the Barrandian area, Czech Republic. In Zhan R. and Huang B. (Eds.), Extended Summary of the International Geoscience Programme IGCP Project 591 Field Workshop, August 2014, Kunming. Nanjing University Press, Nanjing, 97–98. Parsley, R.L. 2012. Ontogeny, functional morphology, and comparative morphology of Lower (Stage 4) and basal Middle (Stage 5) Cambrian gogiids, Guizhou Province, China. Journal of Paleontology, 86, 569-583. Parsley, R.L. and Zhao, Y. 2006. Long stalked eocrinoids in the basal Middle Cambrian Kaili Biota, Taijiang County, Guizhou Province, China. Journal of Paleontology, 80, 1058-1071. Paul, C.R.C. 1988. The phylogeny of the cystoids. In Paul C.R.C. and Smith A.B. (Eds.), Echinoderm Phylogeny and Evolutionary Biology. Clarendon Press, Oxford, 199-213. Paul, C.R.C. and Smith, A.B. 1984. The early radiation and phylogeny of echinoderms. Biological Reviews, 59, 443-481. 92 BODY WALL HOMOLOGIES IN BASAL BLASTOZOANS Peterson, K.J., Arenas-Mena, C. and Davidson, E.H. 2000. The A/P axis in echinoderm ontogeny and evolution: evidence from fossils and molecules. Evolution & Development, 2, 93-101. Prokop, R.J. 1962. Akadocrinus nov. gen., a new eocrinoid from the Cambrian of the Jince area (Eocrinoidea). Sborník Státního geologického Ústavu Československé Republiky, 27, 31-39. Prokop, R. J. and Fatka, O. 1985. Luhocrinus monicae gen. et sp. nov. (Eocrinoidea) from the Middle Cambrian of Bohemia. Věstník Ústředního ústavu geologického, 60, 231-234. Robison, R.A. 1965. Middle Cambrian eocrinoids from western North America. Journal of Paleontology, 39, 355-364. Smith, A.B. 1984. Classification of the Echinodermata. Palaeontology, 27, 431-459. Smith, A.B. 2005. The pre-radial history of echinoderms. Geological Journal, 40, 255-280. Smith, A.B. 2008. Deuterostomes in a twist: the origins of a radical new body plan. Evolution and Development, 10, 493-503. Smith, A.B. and Zamora, S. 2013. Cambrian spiral-plated echinoderms from Gondwana reveal the earliest pentaradial body plan. Proceedings of the Royal Society, Series B: Biological Sciences, 280, 2013197. Smith, A.B., Zamora, S. and Alvaro, J.J. 2013. The oldest echinoderm faunas from Gondwana show that echinoderm body plan diversification was rapid. Nature Communications, 4, 1385. Sprinkle, J. 1973. Morphology and Evolution of Blastozoan Echinoderms. Special Publication of Comparative Zoology Harvard University, Cambridge, Mass., 284 pp. Sprinkle, J. and Guensburg, T.E. 2001. Growing a stalked echinoderm within the Extraxial-Axial Theory. In Barker M.F. (Ed.), Echinoderms 2000. Swets & Zeitlinger, Lisse, 59-65. Sumrall, C.D. and Waters, J.A. 2012. Universal Elemental Homology in glyptocystitoids, hemicosmitoids, coronoids and blastoids: steps towards echinoderm phylogenetic reconstruction in derived Blastozoa. Journal of Paleontology, 86, 956-972. Ubaghs, G. 1968. Eocrinoidea. In Moore R.C. (Ed.), Treatise on Invertebrate Paleontology. Part S: Echinodermata 1(2). Geological Society of America and the University of Kansas Press, Lawrence, S455-S495. Ubaghs, G. 1975. Early Paleozoic echinoderms. Annual Review of Earth and Planetary Sciences, 3, 79-98. Ubaghs G. and Vizcaïno, D. 1990. A new eocrinoid from the Lower Cambrian of Spain. Palaeontology, 33, 249-256. Zamora, S. and Rahman, I.A. 2014. Deciphering the early evolution of echinoderms with Cambrian fossils. Palaeontology, 57, 11051119. Zamora, S. and Smith, A.B. 2011. Cambrian stalked echinoderms show unexpected plasticity of arm construction. Proceedings of the Royal Society, Series B: Biological Sciences, 279, 293-298. Zamora, S., Rahman, I.A. and Smith, A.B. 2012. Plated Cambrian bilaterians reveal the earliest stages of echinoderm evolution. PlosOne, 7, e38296. Zamora, S., Lefebvre, B., Alvaro, J.J., Clausen, S., Elicki, O., Fatka, O., Jell, P., Kouchinsky, A., Lin, J.P., Nardin, E., Parsley, R.L., Rozhnov, S.V., Sprinkle, J., Sumrall, C.D., Vizcaïno, D. and Smith, A.B. 2013a. Cambrian echinoderm diversity and palaeobiogeography. In Harper D.A.T. and Servais T. (Eds.), Early Palaeozoic Biogeography and Palaeogeography. Geological Society, London, Memoirs, 38, 157-171. Zamora, S., Darroch, S. and Rahman, I.A. 2013b. Taphonomy and ontogeny of early pelmatozoan echinoderms: a case study of a massmortality assemblage of Gogia from the Cambrian of North America. Palaeogeography, Palaeoclimatology, Palaeoecology, 377, 62-72. Zhao, Y.L., Huang, Y.Z. and Gong, X.Y. 1994. Echinoderm fossils of Kaili Fauna from Taijian, Guizhou. Acta Palaeontologica Sinica, 33, 305-331. 93