The class Somasteroidea and its significance among early Asterozoa (Echinodermata)
Abstract
Many specimens of the echinoderm subphylum Asterozoa from the Mediterranean Gondwanan Ordovician of France and Morocco have been compiled from many collections, the composite including representation of all four asterozoan classes. While providing a basis for survey of early asterozoan history, the large fauna remains geographically and environmentally localized, and therefore it does not depict Ordovician Asterozoa globally. Overall uniformity of expression has led to widespread agreement on the composition of the subphylum Asterozoa; however, consensus has not been reached on recognition of a precursor (or sister-group) that can clearly advance interpretation of early asterozoan history, a vacancy contributing to differing evaluations in the literature. Based on survey of early skeletal asterozoans, the class Somasteroidea Spencer, 1951 is considered stemward at the subphylum level. Presence of adaxial virgalia (an ontogenetically lengthening series of ossicles, i.e., of discrete virgals) extending laterally from each axial is considered necessary and sufficient for exemplar assignment to the Somasteroidea. Varied adaxial evolutionary histories provide the first steps toward interpretation, recognition, and classification of derived asterozoan lineages. The Somasteroidea is known from seven genera, all reviewed with emphasis on the Mediterranean representatives. The Chinianasteridae Spencer and Villebrunasteridae Fell are recognized at the subfamilial level, and the new subfamily Ophioxenikosinae n. subfam. is described. Recognition of ordinal-level taxonomic subdivisions of the class Somasteroidea is not deemed justified. The two genera Ampullaster Fell, 1963b and Cantabrigiaster Hunter & Ortega-Hernández, 2021 here are considered valid.
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Comptes Rendus Palevol est une revue en flux continu publiée par les Publications scientifiques du Muséum, Paris et l’Académie des sciences, Paris Comptes Rendus Palevol is a fast track journal published by the Museum Science Press, Paris and the Académie des sciences, Paris Les Publications scientifiques du Muséum publient aussi / The Museum Science Press also publish: Adansonia, Geodiversitas, Zoosystema, Anthropozoologica, European Journal of Taxonomy, Naturae, Cryptogamie sous-sections Algologie, Bryologie, Mycologie. L’Académie des sciences publie aussi / The Académie des sciences also publishes: Comptes Rendus Mathématique, Comptes Rendus Physique, Comptes Rendus Mécanique, Comptes Rendus Chimie, Comptes Rendus Géoscience, Comptes Rendus Biologies. Diffusion – Publications scientifiques Muséum national d’Histoire naturelle CP 41 – 57 rue Cuvier F-75231 Paris cedex 05 (France) Tél. : 33 (0)1 40 79 48 05 / Fax : 33 (0)1 40 79 38 40 [email protected] / https://sciencepress.mnhn.fr Académie des sciences, Institut de France, 23 quai de Conti, 75006 Paris. © This article is licensed under the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/) ISSN (imprimé / print) : 1631-0683/ ISSN (électronique / electronic) : 1777-571X Directeurs De la publication / Publication directors : Gilles Bloch, Président du Muséum national d’Histoire naturelle Étienne Ghys, Secrétaire perpétuel de l’Académie des sciences réDacteurs en chef / editors-in-chief : Michel Laurin (CNRS), Philippe Taquet (Académie des sciences) assistante De réDaction / assistant editor : Adenise Lopes (Académie des sciences ; [email protected]) Mise en page / Page layout : Audrina Neveu (Muséum national d’Histoire naturelle ; [email protected]) révisions linguistiques Des textes anglais / english language revisions : Kevin Padian (University of California at Berkeley) réDacteurs associés / associate editors (*, took charge of the editorial process of the article/a pris en charge le suivi éditorial de l’article) : Micropaléontologie/Micropalaeontology Lorenzo Consorti (Institute of Marine Sciences, Italian National Research Council, Trieste) Paléobotanique/Palaeobotany Cyrille Prestianni (Royal Belgian Institute of Natural Sciences, Brussels) Anaïs Boura (Sorbonne Université, Paris) Métazoaires/Metazoa Annalisa Ferretti* (Università di Modena e Reggio Emilia, Modena) Paléoichthyologie/Palaeoichthyology Philippe Janvier (Muséum national d’Histoire naturelle, Académie des sciences, Paris) Amniotes du Mésozoïque/Mesozoic amniotes Hans-Dieter Sues (Smithsonian National Museum of Natural History, Washington) Tortues/Turtles Walter Joyce (Universität Freiburg, Switzerland) Lépidosauromorphes/Lepidosauromorphs Hussam Zaher (Universidade de São Paulo) Oiseaux/Birds Jingmai O’Connor (Field Museum, Chicago) Paléomammalogie (mammifères de moyenne et grande taille)/Palaeomammalogy (large and mid-sized mammals) Grégoire Métais (CNRS, Muséum national d’Histoire naturelle, Sorbonne Université, Paris) Paléomammalogie (petits mammifères sauf Euarchontoglires)/Palaeomammalogy (small mammals except for Euarchontoglires) Robert Asher (Cambridge University, Cambridge) Paléomammalogie (Euarchontoglires)/Palaeomammalogy (Euarchontoglires) K. Christopher Beard (University of Kansas, Lawrence) Paléoanthropologie/Palaeoanthropology Aurélien Mounier (CNRS/Muséum national d’Histoire naturelle, Paris) Archéologie préhistorique (Paléolithique et Mésolithique)/Prehistoric archaeology (Palaeolithic and Mesolithic) Nicolas Teyssandier (CNRS/Université de Toulouse, Toulouse) Archéologie préhistorique (Néolithique et âge du bronze)/Prehistoric archaeology (Neolithic and Bronze Age) Marc Vander Linden (Bournemouth University, Bournemouth) référés / reviewers : https://sciencepress.mnhn.fr/fr/periodiques/comptes-rendus-palevol/referes-du-journal couverture / cover : Holotype of Cantabrigiaster fezouataensis, UCBL-FSL 424 961. Credits: photo by Emmanuel Robert. Comptes Rendus Palevol est indexé dans / Comptes Rendus Palevol is indexed by: – Cambridge Scientific Abstracts – Current Contents® Physical – Chemical, and Earth Sciences® – ISI Alerting Services® – Geoabstracts, Geobase, Georef, Inspec, Pascal – Science Citation Index®, Science Citation Index Expanded® – Scopus®. Les articles ainsi que les nouveautés nomenclaturales publiés dans Comptes Rendus Palevol sont référencés par / Articles and nomenclatural novelties published in Comptes Rendus Palevol are registered on: – ZooBank® (http://zoobank.org)
449 COMPTES RENDUS PALEVOL • 2025 • 24 (23) © Publications scientifiques du Muséum et/and Académie des sciences, Paris. www.cr-palevol.fr Daniel B. BLAKE Department of Earth Sciences and Environmental Change, University of Illinois, 3081 NHB, 1301 West Green Street, 61801 Urbana, IL (United States) [email protected] Bertrand LEFEBVRE Université Claude Bernard Lyon 1, CNRS, LGL-TPE, 2 rue Raphaël Dubois, F-69622 Villeurbanne cedex (France) [email protected] (corresponding author) Submitted on 23 March 2025 | Accepted on 31 May 2025 | Published on 4 November 2025 The class Somasteroidea and its significance among early Asterozoa (Echinodermata) urn:lsid:zoobank.org:pub:C15073D3-DE34-4FB0-97BE-C261F05C0342 Blake D. B. & Lefebvre B. 2025. — The class Somasteroidea and its significance among early Asterozoa ( Echinodermata). Comptes Rendus Palevol 24 (23): 449-487. https://doi.org/10.5852/cr-palevol2025v24a23 ABSTRACT Many specimens of the echinoderm subphylum Asterozoa from the Mediterranean Gondwanan Ordovician of France and Morocco have been compiled from many collections, the composite including representation of all four asterozoan classes. While providing a basis for survey of early asterozoan history, the large fauna remains geographically and environmentally localized, and therefore it does not depict Ordovician Asterozoa globally. Overall uniformity of expression has led to widespread agreement on the composition of the subphylum Asterozoa; however, consensus has not been reached on recognition of a precursor (or sister-group) that can clearly advance interpretation of early asterozoan history, a vacancy contributing to differing evaluations in the literature. Based on survey of early skeletal asterozoans, the class Somasteroidea Spencer, 1951 is considered stemward at the subphylum level. Presence of adaxial virgalia (an ontogenetically lengthening series of ossicles, i.e., of discrete virgals) extending laterally from each axial is considered necessary and sufficient for exemplar assignment to the Somasteroidea. Varied adaxial evolutionary histories provide the first steps toward interpretation, recognition, and classification of derived asterozoan lineages. The Somasteroidea is known from seven genera, all reviewed with emphasis on the Mediterranean representatives. The Chinianasteridae Spencer and Villebrunasteridae Fell are recognized at the subfamilial level, and the new subfamily Ophioxenikosinae n. subfam. is described. Recognition of ordinal-level taxonomic subdivisions of the class Somasteroidea is not deemed justified. The two genera Ampullaster Fell, 1963b and Cantabrigiaster Hunter & Ortega-Hernández, 2021 here are considered valid. KEY WORDS Somasteroidea, Asterozoa, Ordovician, morphological evolution, new subfamily.
450 COMPTES RENDUS PALEVOL • 2025 • 24 (23) Blake D. B. & Lefebvre B. INTRODUCTION A large and diverse specimen array of Asterozoa recovered from the Ordovician of France and Morocco has enabled reevaluation of aspects of early subphylum diversification (Blake & Lefebvre 2024; Glass etal. 2024). Reevaluation continues here with survey of the class Somasteroidea Spencer, 1951, the survey beginning with the following perspectives, some tendentious. The subphylum Asterozoa as compiled by Ubaghs (1953) and Spencer & Wright (1966) is accepted as monophyletic. Interpretations are based on the fossil record; enduring debates surrounding significance of early development of extant taxa (e.g. Fell 1948; Smith 1984) are not treated. The earliest-known skeletal asterozoans are earliest Ordovician (Tremadocian). Ambiguous trace fossils suggest Cambrian occurrence of at most only lightly calcified representatives (Alpert 1976; Mikulás 1992). The abrupt diversity of the earliest asterozoans is consistent with an interpretation of clade diversifications prior to first appearances in the fossil record (e.g. Erwin etal. 2011). Asterozoan derivation is controversial in the literature. Two potential ancestral or sister-group candidates, the Edrioasteroidea Billings, 1858 (e.g. Dean Shackleton 2005) and the Crinoidea Miller, 1821 (e.g. Fell 1963a; Hunter & OrtegaHernández 2021) have been favored. Additionally, problematic Camptostroma Ruedemann, 1933, has been selected (Smith & Jell 1990). Alternatively, no known Cambrian or other Early Ordovician echinoderm is similar enough to any asterozoan as to provide a well-supported sister-group (e.g. Blake 2013), “acceptable” meaning that the requisite changes between the sister-group designate and known early asterozoans are great enough as to be considered at least as likely to mislead as to usefully guide. Fundamental differences among Camptostroma, early Edrioasteroidea, and early Crinoidea serve to exemplify uncertainties. Evaluations do not reject the nominates, rather they argue that supporting data are inadequate. The Somasteroidea is accepted as stemward in the subphylum. Known somasteroids are few, at least in part because of epifaunal habits and delicate construction, the limitations hindering interpretations. Guidelines for specimen assignment are needed. Presence of proximally-lengthening virgalia is necessary and sufficient for specimen assignment to the Somasteroidea. Presence of two to four virgal derivatives extending laterally from each axial is necessary and sufficient for specimen assignment to the Stenuroidea. Potential for phylogenetic complexities within these designated limitations are recognized; however, use is considered justified by the present state of knowledge while providing objective points of departure for future evaluations. Representatives of both the Asteroidea de Blainville, 1830 and Ophiuroidea Gray, 1840 have a single adaxial virgal derivative, the so-called adambulacral of asteroids and lateral of ophiuroids. As emphasized by Spencer (19141940, 1951; also Glass etal. 2024), assignment of many early exemplars at the class level is difficult thereby requiring use of additional criteria. Most important but not categorical, ophiuroid axials and commonly upright plate-like adaxials are laterally aligned, and an ambulacral furrow is absent, whereas an ambulacral furrow is developed among asteroids, the axials partially to fully displaced onto the aboral surface of approximately equidimensional adaxials. Partial displacement with broad furrows is characteristic of more stemward asteroids with full displacement onto the aboral adaxial surface and relatively narrow furrows characterizing the more derived (Blake 2018). Adaxial expressions of a number of problematic genera are variously uncertain and ambiguous (e.g. Blake 2000, 2007, 2014, 2024). RÉSUMÉ La classe Somasteroidea et son importance au sein des premiers astérozoaires (Echinodermata). L’Ordovicien de France et du Maroc (Province méditerranéenne) a livré des assemblages particulièrement abondants et diversifiés d’échinodermes comprenant notamment des représentants des quatre classes d’astérozoaires. Ce matériel permet d’analyser comment se sont déroulées les premières étapes de la diversification de ce sous-phylum dans les mers australes du domaine péri-gondwanien. Dès leur apparition dans le registre fossile, les astérozoaires partagent un certain nombre d’apomorphies qui permettent de les identifier sans hésitation. Cette grande uniformité pose par contre le problème de leur origine et de l’identification d’un groupe-frère au sein des échinodermes. L’examen des plus anciens restes connus d’astérozoaires suggère que la classe Somasteroidea Spencer, 1951 occupe une position basale à l’échelle du sous-phylum. Les somastéroïdes sont caractérisés par la possession de plaques virgales adaxiales qui s’étendent latéralement depuis chaque axiale. L’analyse de l’expression très variable de ces adaxiales chez les somastéroïdes permet de décrypter une histoire évolutive complexe conduisant aux patterns plus dérivés observés dans les trois autres classes. Les somastéroïdes ne sont connus que par sept genres, dont six proviennent de l’Ordovicien inférieur à moyen de la Province méditerranéenne. Différentes sous-familles sont identifiées au sein des Chinianasteridae et des Villebrunasteridae, dont une est nouvelle (Ophioxenikosinae n. subfam.). Les genres Ampullaster Fell, 1963b et Cantabrigiaster Hunter & Ortega-Hernández, 2021 sont ici reconnus comme valides. MOTS CLÉS Somasteroidea, Asterozoa, Ordovicien, évolution morphologique, sous-famille nouvelle.
451 Somasteroidea and early Asterozoa COMPTES RENDUS PALEVOL • 2025 • 24 (23) Skeletal development, taxonomy, and history of the subphylum Asterozoa have been treated by a number of authors (Agassiz 1877; Viguier 1879; Spencer 1951; Ubaghs 1953; Fell 1963a; Spencer & Wright 1966; Dean Shackleton 2005; Blake 2013, 2018; Blake & Guensburg 2015; Gladwell 2018; Villier etal. 2018; Blake & Hotchkiss 2022). Figures 1 through 14 illustrate somasteroid morphology based on earlier reconstructions (Figs 1; 12A, C, E) and photographic documentation (Figs 2-11; 12B, D, F-14). Problematic specimens (Fig. 14) exemplify diversity while illustrating complexities of incomplete preservation. TERMINOLOGY The aboral surface is directed toward the water column, the oral surface, toward the substrate. The primary skeleton forms the body wall. The accessory skeleton includes the spines, spinelets, granules, and pedicellariae seated on all primary ossicles except axials. Accessories are not a part of the primary skeleton. Axial (ambulacral a synonym) ossicles form a double series along the axis of the arm. Podial basins of most asterozoans, although commonly more or less obscured in preservation, are either approximately shared between successive axials (Figs 2B, C; 3C; 4A, B; 7E; 8D, F), or the basin lies almost entirely on one side of the transverse ridge (Figs 10-12). Interpretation of axial shape can be ambiguous in part because of incomplete preservation and in part because of integrated series deflection accompanying preservation. A few axials are enlarged, asymmetrical, and contain portions of multiple basins rather than only a shared basin on each side of the transverse ridge (Figs 1B; 6B, C); no suggestion of fusion of discrete ossicles has been recognized, and therefore interpretation is that the configuration represents a single ossicle, termed compound, rather than the product of ontogenetic fusion of more than one ossicle. The unpaired terminal is at the arm tip, presence generally difficult to verify among fossils, especially so among somasteroids. Mouth-angle ossicles are the proximal-most paired ossicles of the axial series; an unpaired ossicle, the torus (dental plate of Dean Shackleton (2005: char. 148, a synonym) is found on the oral side of the pair of some stem-group asterozoans. The adaxial skeleton as treated herein consists of the full linear series abutting each axial and directed abradially. In the Somasteroidea, each ossicle of the series is termed a “virgal”, a single series a “virgalium”, and multiple series “virgalia”. In the Stenuroidea, virgalia were phylogenetically reduced to one or three “embedded virgals” and an “outer virgal” and reduced to the “adambulacral” of the Asteroidea and the “lateral” of Ophiuroidea. The remainder of the skeleton is extraxial. The body can be edged by a single or double series of more or less clearly differentiated marginal ossicles. Because the term “marginal” has been broadly applied within echinoderms with unclear implications of homology, the genetically neutral term ambital framework was proposed (Blake 2013). A single marginal series has been judged to be homologous throughout stem-group asteroids, it recognized as inferomarginal. All skeletal components “above” or seaward of the inferomarginals for convenience are referred to as aboral, including any superomarginal and intermarginal series, and in some taxa, the madreporite. The axillary (odontophore) typically is a more or less clearly differentiated unpaired ossicle, among Paleozoic asteroids typically external and aligned with the inferomarginal series at the interbrachial midline. Abactinal ossicles are aboral to the marginal series; see discussion below under Abactinals. A medial disk centrale can be recognized in some exemplars, it enclosed by a ring of more or less differentiated ossicles, a primary circlet or aboral ring. Midarm ossicles can be enlarged and/or otherwise differentiated to form a carinal series, and in many asteroids, lateral differentiated abactinal series or adradialia are aligned with midarm carinals. A hydropore or madreporite provides opening to the water-vascular system (edited from Blake & Lefebvre 2024). AbbreviAtions Institutional abbreviations AA Université Cadi Ayyad, Marrakesh; MBB Musée du Biterrois, Béziers; MHNN Muséum d’Histoire naturelle, Nantes; MNHN Muséum national d’Histoire naturelle, Paris; NMP Národní Muzeum, Prague; PRI Prairie Research Institute, University of Illinois, Urbana-Champaign; UCBL-FSL Collections de paléontologie, Université Claude Bernard Lyon 1, Villeurbanne; YPM Yale Peabody Museum, Yale University. Other abbreviation MAO mouth-angle ossicles. TAPHONOMY AND OCCURRENCES For the most of geologic history, authors have recognized two classes (or subclasses) of the subphylum Asterozoa, the Asteroidea and Ophiuroidea, but reasoning and outcomes surrounding class subdivisions have differed (for Paleozoic occurrences, see Spencer 1914-1940, 1951; Ubaghs 1953; Fell 1963a, b; Spencer & Wright 1966; McKnight 1975; Smith & Jell 1990; Dean 1999; Mooi & David 2000; Dean Shackleton 2005; Blake 2013, 2018, 2024; Blake & Guensburg 2015; Villier etal. 2018). Usage here of a four-fold subphylum partitioning (Blake 2013, 2024) does not argue finality but rather serves in part to emphasize the diversity and complexity of the earliest asterozoans, an interpretation indirectly exemplified by usage of “plesion” categories (Dean Shackleton 2005) and recognition of genera left unassigned at the class level (Blake 2000, 2014; Blake etal. 2020). The many proportionately small skeletal elements of asterozoans are seated in soft tissues, and therefore individuals are readily disrupted and destroyed with death and decay (e.g. Brett etal. 1997; Gorzelak & Salamon 2013; Fraga & Vega 2024). Specimen remains are all but inevitably incomplete in various ways. Essentially planar, only one surface of many or most specimens is available, and even if both part and coun-
452 COMPTES RENDUS PALEVOL • 2025 • 24 (23) Blake D. B. & Lefebvre B. terpart remain, the margins of curved and partially collapsed disks and arms typically are variably obscured. If the specimen is essentially intact, accessories hide primary skeletal elements, and morphological and positional details of abutted ossicles and internal ossicular surfaces are incompletely available. Ossicular detail is readily lost with outcrop weathering. The relatively abundant and diverse Mediterranean Gondwanan fauna partially inverts the more usual difficulties, the fossils including many very fragmentary specimens demanding ongoing reevaluation of taxon limits. Although initially not recognized at a higher taxonomic level, somasteroid fossils were first described from Early Ordovician Montagne Noire localities of the south of France (Thoral 1935) and the Middle Ordovician of Czech Republic (Spencer 1951). This limited distribution was broadened with description of Ophioxenikos Blake & Guensburg, 1993, from the Floian of Nevada, United States, and reports of somasteroids in the Lower Ordovician Fezouata Shale of the Anti-Atlas, Morocco (Lefebvre etal. 2016). Markedly different environmental settings are represented. The Czech, French, and Moroccan specimens were all collected from high latitude Mediterranean Gondwanan siliciclastic sequences interpreted as deposited in relatively distal, cool, and presumably relatively quiet waters, below storm wave-base (Vizcaïno & Lefebvre 1999; Lefebvre 2007; Lefebvre etal. 2016, 2022). The equatorial Laurentian source outcrop of the only specimen of Ophioxenikos consists of interbedded calcisiltites alternating with calcarenites, some of the latter preserved as megaripples extending into mounds, the outcrop interpreted as deposited in shallow, warm waters. No other fossils were recovered from the small outcrop of the Ophioxenikos specimen. No definitive data are available to determine which geography and morphological expressions more closely reflect the stemward somasteroid condition, although Ophioxenikos is younger. Archegonaster Jaekel, 1923 and Ophioxenikos have been reviewed in some detail (Spencer 1951; Smith & Jell 1990; Dean Shackleton 2005; Blake & Guensburg 2015) and treatment here is limited. Geological context and paleo environmental conditions associated with occurrences of Early Ordovician somasteroids from the Montagne Noire (southern France) and the Anti-Atlas (Morocco) are summarized below. In part seeking to more broadly document somasteroid diversity, Ampullaster Fell, 1963b, and Cantabrigiaster Hunter & Ortega-Hernández, 2021, are recognized here, although previously challenged. MontAgne noire In southern France, the Montagne Noire yielded the most abundant and diverse assemblage of somasteroids in the world (over 30 specimens belonging to four taxa). The available material is the result of over 150 years of sampling mostly in the surroundings of Caunes-Minervois (Aude), FélinesMinervois (Hérault) and Saint-Chinian (Hérault). This material is deposited in the paleontogical collections of the Musée du Biterrois, Béziers (Griffe collection), the Muséum national d’Histoire naturelle, Paris (Courtessole-Griffe, and Vizcaïno collections), and the Université Claude Bernard Lyon 1, Villeurbanne (Lignières, Marty, Monceret, Thoral, Villebrun, and Vizcaïno collections). In the Montagne Noire, the Lower Ordovician corresponds to an almost continuous sedimentary succession comprising the uppermost part of the Val d’Homs/La Gardie Formation, as well as the overlying La Dentelle, Saint-Chinian, La Maurerie, Cluse de l’Orb, Foulon and Landeyran formations (Courtessole etal. 1981, 1983, 1985, 1988; Vizcaïno etal. 2001; Vizcaïno & Álvaro 2003; Lefebvre etal. 2023). This succession records two large scale regressive-transgressive cycles, with the alternation of proximal, sandstone-dominated units (La Dentelle and Cluse de l’Orb formations) and distal, shale and siltstonedominated units (Saint-Chinian and Landeyran formations), separated by transitional facies and lithologies (Val d’Homs/ La Gardie, La Maurerie, and Foulon formations) (Vizcaïno etal. 2001; Tortello etal. 2006). Biostratigraphy of the Lower Ordovician of the Montagne Noire relies primarily on trilobites (Vizcaïno & Álvaro 2003), with rare additional data based on agnostids (Tortello etal. 2006) and conodonts (Serpagli etal. 2007). The Val d’Homs/ La Gardie Formation is a 60 to 300 m thick unit consisting mainly of shales and intercalated limestones. This formation has yielded both typical Furongian (late Cambrian) brachiopods, echinoderms and trilobites (Feist & Courtessole 1984; Ubaghs 1998) and, in its uppermost levels, a typical early Tremadocian trilobite assemblage (Proteuloma geinitzi trilobite Zone; Vizcaïno & Álvaro 2003). This suggests that the Cambrian-Ordovician boundary occurs within the upper part of the Val d’Homs/La Gardie Formation. The overlying sandstones of the La Dentelle Formation are azoic (Vizcaïno etal. 2001). The next unit, the Saint-Chinian Formation, is over 500 m thick and consists primarily of shales and fine siltstones, with numerous levels of fossiliferous siliceous concretions. The age of the lower part of the Saint-Chinian Formation is particularly well-constrained based on its diverse trilobite (Shumardia pusilla trilobite Zone; Vizcaïno & Álvaro 2003), agnostid (Tortello etal. 2006) and conodont faunas (Serpagli etal. 2007), all indicating a middle Tremadocian age (Paltodus deltifer conodont Zone; for global correlation, see e.g. Bergström etal. 2009; Goldman etal. 2020). The long suspected late Tremadocian age of the middle (Euloma filacovi trilobite Zone) and upper parts (base of the Taihungshania miqueli trilobite Zone) of the Saint-Chinian Formation was confirmed by their particularly diverse agnostid assemblages (Tortello etal. 2006). The occurrence of typical early Floian agnostid taxa in the overlying, particularly thick (900 m) La Maurerie Formation suggests that the Tremadocian-Floian boundary more or less coincides with the transition between the Saint-Chinian and La Maurerie formations (Tortello etal. 2006; Van Iten & Lefebvre 2020; Lefebvre etal. 2023). The age of the three overlying units is less constrained, and relies solely on trilobite assemblages suggesting a mid Floian age for the Cluse de l’Orb (Colpocoryphe maynardensis Zone) and Foulon (Neseuretus (N.) arenosus Zone) formations, and a late Floian age for the Landeyran Formation (Apatokephalus incisus and Hangchungolithus primitivus zones) (Van Iten & Lefebvre 2020; Lefebvre etal. 2023).
453 Somasteroidea and early Asterozoa COMPTES RENDUS PALEVOL • 2025 • 24 (23) The four somasteroid taxa Ampullaster ubaghsi Fell, 1963b, Chinianaster levyi Thoral, 1935, Thoralaster spiculiformis Dean Shackleton, 2005 and Villebrunaster thorali Spencer, 1951were found in siliceous concretions of the middle part of the SaintChinian Formation (Euloma filacovi Zone; Vizcaïno & Lefebvre 1999; Vizcaïno etal. 2001). In the Montagne Noire, these levels have yielded the most abundant and diverse assemblage of the whole Lower Ordovician succession (Vizcaïno etal. 2001). Faunas are dominated by trilobites, but they also comprise numerous annelids (machaeridians), brachiopods, conulariids, graptolites, hyolithids, and molluscs (bivalves, cephalopods, gastropods, rostroconchs, tergomyans) (Thoral 1935; Capéra etal. 1978; Babin etal. 1982; Courtessole etal. 1983; Vidal 1996a; Vizcaïno etal. 2001; Vizcaïno & Álvaro 2003; Kröger & Evans 2011; Van Iten & Lefebvre 2020). The middle part of the Saint-Chinian Formation has also yielded one of the most diverse late Tremadocian echinoderm assemblages in the world (Vizcaïno & Lefebvre 1999; Sprinkle & Guensburg 2004; Lefebvre etal. 2013). This assemblage is dominated by unattached epibenthic taxa, well-adapted to the life on soft siliciclastic substrates: primarily cornute and mitrate stylophorans, but also asterozoans (somasteroids, stenuroids), glyptocystitid rhombiferans and solutans (Vizcaïno & Lefebvre 1999; Lefebvre & Fatka 2003). Crinoids, edrioasteroids and eocrinoids are also present, but they represent minor components of benthic communities (Vizcaïno & Lefebvre 1999; Lefebvre & Fatka 2003). The preservation of nearly complete, articulated to slightly disarticulated echinoderm skeletal remains is suggestive of quiet, relatively distal (shelf) environmental conditions, below storm wave base (Vizcaïno & Lefebvre 1999; Lefebvre 2007). Chinianaster levyi also occurs in siliceous concretions of the uppermost part of the Saint-Chinian Formation (base of the Taihungshania miqueli Zone; Vizcaïno & Lefebvre 1999; Vizcaïno etal. 2001). These late Tremadocian levels have also yielded particularly diverse marine assemblages, dominated by trilobites, associated with brachiopods, conulariids, graptolites, hyolithids, machaeridians and molluscs (Vizcaïno etal. 2001). Although less diverse than in the underlying Euloma filacovi Zone (e.g. glyptocystitids and stenuroids are absent), echinoderms still represent a major component of epibenthic assemblages (Vizcaïno & Lefebvre 1999; Vizcaïno etal. 2001). In these levels, cornutes and kirkocystid mitrates are the most abundant echinoderm taxa. Taphonomic and environmental conditions are similar to those of the E. filacovi Zone (Vizcaïno & Lefebvre 1999; Vizcaïno etal. 2001). Anti-AtlAs In the Anti-Atlas (Morocco), the first specimens of Early Ordovician somasteroids were collected in the early 2000s (Van Roy etal. 2010; Lefebvre etal. 2016). In the last 20 years, intensive scientific and commercial sampling in this region yielded several dozens of specimens, with c. 50 of them deposited in the paleontological collections of the Museum of Comparative Zoology, Cambridge, Massachusetts (United States), the Prairie Research Institute, Champaign, Illinois (United States), the Université Claude Bernard Lyon 1, Villeurbanne (France), the Université Cadi Ayyad, Marrakesh (Morocco), and the Yale Peabody Museum, New Haven, Connecticut (United States). However, in spite of a high number of available specimens, taxonomic diversity remains lower than in the Montagne Noire, with a single somasteroid described so far (Cantabrigiaster fezouataensis Hunter & Ortega-Hernández, 2021 [Hunter & Ortega-Hernández 2021; Blake & Hotchkiss 2022]). Most specimens deposited in public collections were collected in the Ternata plain, c. 15 to 30 km N of Zagora, although their precise locality and stratigraphic position are often approximative. Somasteroids belonging to the Prairie Research Institute come from Jbel Kissane (Agdz area), about 68 km NW of Zagora. In the Agdz and Zagora areas, the c. 900 m thick Lower Ordovician deposits are unconformably overlying the Guzhangian (middle Cambrian) sandstones of the Tabanite Group (Destombes etal. 1985; Martin etal. 2016a). In the Anti-Atlas, the Lower Ordovician succession is traditionally subdivided into the Lower Fezouata, Upper Fezouata, and Zini formations (Destombes etal. 1985; Álvaro etal. 2022). All together, these three units record a single long-term eustatic cycle, with the maximum flooding surface coinciding more or less with the boundary between the Lower and Upper Fezouata formations (Destombes etal. 1985; Vidal 1996b; Lefebvre etal. 2016; Vaucher etal. 2016). In the Agdz and Zagora areas, in the absence of the iron-rich glauconitic bed which marks the limit between the Lower and Upper Fezouata formations, these two units are generally considered as forming together the Fezouata Formation, consisting of c. 850 m of fine siltstones (Lefebvre etal. 2016, 2018; Martin etal. 2016a; Vaucher etal. 2016, 2017). The overlying black sandstones of the Zini Formation represent the proximal-most deposits of the Lower Ordovician succession (Vaucher etal. 2016, 2017). They are unconformably overlain by the Darriwilian shales of the Tachilla Formation (Dapingian gap; Destombes etal. 1985). Biostratigraphy of the Lower Ordovician succession in the Central Anti-Atlas is well-constrained, and based on conodonts (Lehnert etal. 2016), graptolites (Destombes 1960; Gutiérrez-Marco & Martin 2016; Martin etal. 2016a), and palynomorphs (acritarchs and chitinozoans; Elaouad-Debbaj 1984, 1988; Nowak etal. 2016). Ages obtained from these different taxonomic groups can be readily compared with other regions, therefore allowing correlation of the Moroccan deposits with the international time scale (Lefebvre etal. 2018). The lowermost 250 m of the Fezouata Formation (earlmiddle Tremadocian, Anisograptus matanensis to Aorograptus victoriae graptolite zones; Gutiérrez-Marco & Martin 2016) have yielded depauperate, low-diversity assemblages (Destombes etal. 1985; Lefebvre etal. 2016). In marked contrast, the overlying 150 m are extremely fossiliferous and comprise the c. 70 m thick interval, where most taxa of the late Tremadocian Fezouata Biota were collected (Sagenograptus murrayi graptolite Zone; Van Roy etal. 2010; Lefebvre etal. 2016, 2018; Martin etal. 2016a; Saleh etal. 2020a, 2021, 2024). This interval yielded extremely abundant and diverse fossil remains, comprising not only taxa with a recalcitrant
454 COMPTES RENDUS PALEVOL • 2025 • 24 (23) Blake D. B. & Lefebvre B. organic skeleton (graptolites) or mineralized hard parts (bivalves, brachiopods, cephalopods, conulariids, echinoderms, gastropods, hyolithids, machaeridians, ostracods, rostroconchs, tergomyans, and trilobites), but also a wealth of more lightly skeletonized organisms seldom preserved in the fossil record (e.g. aglaspidids, demosponges, eurypterids, lobopodians, marrellomorphs, paleoscolecids, radiodonts, xyphosurans) (Destombes etal. 1985; Botting 2007, 2016; Vinther etal. 2008, 2017; Van Roy etal. 2010, 2015; Van Roy & Briggs 2011; Kröger & Lefebvre 2012; Ebbestad 2016; GutiérrezMarco & Martin 2016; Lefebvre etal. 2016; Martí Mus 2016; Martin etal. 2016b; Polechová 2016; Van Iten etal. 2016; Drage etal. 2023; Laibl etal. 2023; Potin etal. 2023; Candela etal. 2024; Lustri etal. 2024). Echinoderms are one of the major components of the late Tremadocian Fezouata Biota (Lefebvre etal. 2016). All specimens of the somasteroid Cantabrigiaster fezouataensis were apparently collected in this c. 70 m thick interval (with the limitation of approximative locality information, when the material was acquired from local fossil traders). Echinoderm assemblages are dominated by epibenthic, vagrant taxa, primarily cornute stylophorans, along with glyptocystitid rhombiferans, mitrates, somasteroids, and solutans (Lefebvre & Botting 2007; Lefebvre etal. 2016; Hunter & Ortega-Hernández 2021; Dupichaud etal. 2023). Eocrinoids can be also locally abundant (Allaire etal. 2017), while permanently attached taxa (crinoids, diploporitans, edrioasteroids) are extremely rare (Sumrall & Zamora 2011; Lefebvre etal. 2016). The preservation of echinoderms illustrating various stages of decay, some of them with exceptionally preserved soft parts (Lefebvre etal. 2019; Saleh etal. 2023), implies their burial by occasional distal storm deposits in an otherwise quiet, distal (shelf) environment. No soft parts have been observed so far in C. fezouataensis; putative carbonaceous films observed in podial basins of some specimens are the result of latex casting (Saleh etal. 2020b). In the Agdz-Zagora area, the upper part of the Fezouata Formation (early-late Floian, Cymatograptus? protobalticus Zone to “Azygograptus interval”; Gutiérrez-Marco & Martin 2016; Lefebvre etal. 2018) consists of micaceous siltstones, with some siliceous concretion-bearing levels, and towards the top of this unit, more and more frequent and thicker intercalated sandstone beds (Vaucher etal. 2016, 2017). Within this 400 m thick succession, exceptional preservation has been recorded in a narrow, c. 50 m thick interval (Baltograptus? jacksoni Zone, mid Floian; Lefebvre etal. 2018). However, lightly sclerotized taxa are far less numerous and diverse than in the late Tremadocian Fezouata Biota (Lefebvre etal. 2018; Saleh etal. 2024). In the Central Anti-Atlas, Floian assemblages are dominated by brachiopods, molluscs and trilobites, along with conulariids, echinoderms, graptolites, hyolithids, and ostracods (Destombes etal. 1985; Kröger & Lefebvre 2012; Ebbestad 2016; Gutiérrez-Marco & Martin 2016; Lefebvre etal. 2016; Martin etal. 2016b; Polechová 2016; Van Iten etal. 2016; Candela etal. 2024). In the upper part of the Fezouata Formation, echinoderm assemblages are dominated by various epibenthic taxa adapted to life on soft, siliciclastic substrates: primarily eocrinoids (e.g. Balantiocystis), as well as glyptocystitid rhombiferans, solutans, and stylophorans (Chauvel 1966, 1971; Lefebvre etal. 2016; Saleh etal. 2022; Dupichaud etal. 2023). Crinoids and edrioasteroids are rare (Donovan & Savill 1988; Sumrall & Zamora 2011; Lefebvre etal. 2016). Somasteroid remains are also present, in both siltstones and siliceous concretions; however, their preservation hinders so far any more precise taxonomic identification (Lefebvre etal. 2016). INTERPRETING THE SOMASTEROIDEA: REVIEW OF THE LITERATURE To emphasize the evolution of interpretation, citations are chronological and authors recur. Titles not specifically addressing the Somasteroidea but nevertheless germane are included. Spencer 1914-1940. — Nearly all named Paleozoic asterozoan genera were surveyed, the author finding exemplar morphology converged back in time such that many genera could not be assigned at the (sub)class level. Rather than strict usage of Linnaean terminology, eight subdivisions termed “Sections” were recognized. The somasteroids Archegonaster and Chinianaster Thoral, 1935 were not included. Spencer 1919. — The new genus Platanaster Spencer, 1919 was described from the Late Ordovician and assigned with Palasteriscus Stürtz, 1886 from the Early Devonian to the new family Platanasteridae Spencer, 1919. Familial recognition emphasized a shared flattened form in which the adambulacral ossicles are broad, their alignment with the ambulacral ossicles yielding a shallow ambulacral groove, these expressions emphasized in an interpretation of asterozoan origins (Fell 1963a). The Platanasteridae was not assigned at the class level. Jaekel 1923. — Archegonaster was recognized in a brief study encompassing the morphological diversity of Asterozoa. Archegonaster was found to combine a primitive internal construction with an external form comparable to that of the living asteroid Goniaster Agassiz, 1836. Spencer 1927. — The family Archophiactinidae was recog - nized for three genera, these poorly known and not assigned to subclass but judged “nearly related to primitive Asterozoa” and “lying near root genera which gave rise to some of the Palaeozoic Ophiuroidea” (p. 360). Thoral 1935. — Chinianaster was recognized, its unique nature among asterozoans not clearly identified. Spencer 1951. — The author’s last sole-authorship title. Interpretations summarized in the abstract included recognition of the Somasteroidea, it interpreted as “the first stages in the differentiation of a starfish” (p. 87), the term “starfish” used as a collective for all Asterozoa. Three subclasses were recognized, the Ophiuroidea, Asteroidea, and the exclusively Early and Middle Ordovician Somasteroidea. Use of “subclass” rather than “class” was not discussed; however, in Spencer (1914-1940), affinities of many genera, whether asteroid or ophiuroid, were found to be indeterminate thereby seemingly implying differences between groups were not of a level that warranted class-level recognition.
455 Somasteroidea and early Asterozoa COMPTES RENDUS PALEVOL • 2025 • 24 (23) All somasteroids were assigned to a single new order “Goniactinida”. Two new familial concepts were recognized, the Chinianasteridae Spencer, 1951 for Chinianaster and thennew Villebrunaster Spencer, 1951, and the Archegonasteridae limited to Archegonaster. Linnaean terms below the subclass level were cited, the earlier “Section” usage abandoned. Function was stressed (p. 87): “grouping of the starfish adopted here is based on the activities of the arms, especially during feeding”, the asteroid arm “from the beginning is adapted for a carnivorous diet of large food” whereas for ophiuroids, feeding depended on “small food in or near the sea bottom”, the “primitive” representatives with a “burrowing habit”. The Somasteroidea was thought to include the earliest asterozoan occurrences (Tremadocian, the others Arenig [Floian]) representing the “first stages in the differentiation of a starfish”. Comparisons with extant crinoids were provided. Although many photographs were included, details are obscure, the reader referred to diagrammatic reconstructions, some calling for reevaluation (e.g. below on Spencer 1951: fig. 7). The diagnostic characters of the Somasteroidea (p. 91) stressed presence of only two oral-surface ossicular types, the “ambulacralia” and rows of “interambulacralia” (or “virgalia”). The latter were found “especially characteristic”, although nevertheless “entirely wanting” among “later genera”, the “later” not clearly identified. The “ambulacralia” also were found to be “characteristic”. The aboral skeleton, “when present”, was described as a reticulate meshwork of multiradiate ossicles. For the Asteroidea, the order Platyasterida was recognized for the Platanasteridae. Two new orders of Ophiuroidea were recognized and distinguished based on presence of “vertebrae”, the Stenurida in which “vertebrae” were lacking, and the Ophiurida, in which they are present. “Vertebrae” was not clearly defined for the Stenurida; however, the laterals “usually” occur as a double series, these termed “laterals” and “sublaterals”. Historically, it was noted that starfish had “arrived in a series of transgressions which began in the Tremadocian”, the use of “arrive” seemingly implying earlier occurrences elsewhere, although a broader reading might argue a phylogenetic “arrival”. Villebrunaster was judged a suspension feeder, a habit that served to connect it with a “probably ciliary pelmatozoan ancestor” (p. 91). The potential for ciliary feeding was discussed (p. 96). Ubaghs 1953. — In a comprehensive survey of early asterozoans, morphology was reviewed and the taxonomic subdivisions of Spencer (1951) retained (p. 813). Three families (Archegonasteridae, Archophiactinidae, Chinianasteridae) were assigned to the Somasteroidea. In a diagrammatic reconstruction (fig. 64, p. 837), Paleozoic and post-Paleozoic asterozoans were separated and somasteroids were assigned a stemward positioning. Many subdivisions were recognized; however, no direct linkages between those of the Paleozoic and the post-Paleozoic were proposed. Fell 1963a. — In a detailed series of contributions including 1963a, Fell hypothesized a phylogenetic sequencing in which the Crinoidea were seen as ancestral to the Asterozoa. Interpretation focused on inferred “growth gradients” in which so-called lateral gradients represented by the pinnules of the crinoid arm evolved into the laterally radiating virgalia of somasteroids, the latter in Fell’s terminology, “metapinnules”. The living asteroid genus Platasterias Gray, 1871 was reassigned to the Somasteroidea and envisioned as transitional to derived asterozoans. Virgalia in turn transitioned to the longitudinal growth gradients of the Asteroidea, first the fossil Platanasteridae, next the extant Luidiidae, finally to more derived asteroids (Fell 1963a: 391, 395, table 1, fig. 7). A parallel sequencing was envisioned for the Ophiuroidea. In an extended and detailed discussion, the “sublateral” of stenuroids represent a first phase as the ancestral virgalia progressed to the single lateral of derived ophiuroids (Fell 1963a: 403, 410, table 2). Fell 1963b. — A new Ordovician somasteroid Ampullaster was proposed (Fell 1963b), and it and Villebrunaster Spencer were assigned to the new Villebrunasteridae. Philip 1965. — The broader conclusion of Fell (1963a), the proposed derivation of the Asterozoa from the Crinoidea, was rejected. Relationships between extant asterozoans and Ordovician somasteroids were not discussed. Spencer & Wright 1966. — In a summary discussion, Wright noted that a classification of asterozoans of all ages had been outlined but not completed prior to the 1954 passing of Spencer. The chapter was completed by Wright emphasizing the thinking of Fell, including interpretation of extant Platasterias as a surviving somasteroid. In a cautionary phrasing, however, Fell’s derivation of somasteroids from crinoids only “seems to be true” (p. 31). Expanding on the earlier two-fold subdivision of the somasteroid oral skeleton (“ambulacralia” and “interam - bulacralia” Spencer 1951), a seminal three-fold subdivision – “axial”, “adaxial”, and “extraxial” – was proposed, it providing a descriptive classification while also drawing attention to issues surrounding the interpretation of homologies among skeletal series. Somasteroids, asteroids, and ophiuroids were recognized as subclasses of the class Stelleroidea Lamarck, 1816 somasteroids ancestral to the other two (e.g. fig. 38). The Villebrunasteridae (for Villebrunaster, Ampullaster), the monogeneric Platasteriidae, and Archophiactinidae were retained as families of Somasteroidea. Among asteroids, the Palasteriscidae (for Platanaster, Palasteriscus) Gregory replaced the junior name Platyasterida Spencer, and it and the extant Luidiidae were assigned to the Platyasterida. The term Ophiurida was abandoned. Madsen 1966. — In a brief treatment, the interpretation of Platasterias as a somasteroid (Fell 1963a) was rejected. Ubaghs 1967. — Somasteroids were treated as ancestral to both asteroids and ophiuroids, the three recognized at the subclass level. Neither the crinoid nor edrioasteroid ancestry was found convincing (p. 56). Blake 1972, 1982. — Based on comparison among discrete ossicle types, Platasterias was removed from the Somasteroidea, recognized as a subgenus of extant Luidia Forbes, 1839, and returned to the Asteroidea. Döderlein (1920) subdivided
462 COMPTES RENDUS PALEVOL • 2025 • 24 (23) Blake D. B. & Lefebvre B. virgals, and therefore insertion of a new ossicle would not demand interruption of the continuing virgalium growth sequence; however, treatment as a terminal accessory would call for insertion of new virgals within the growth sequence. Further, as few accessories have been recognized among somasteroids, radioles as true accessories would be striking because of both presence and form. Because radioles are recognized only at body margins, they are tentatively interpreted as aberrancies accompanying slowing of growth later in life, perhaps associated with body flexure, and therein, teratological. Accessories Accessories are extraxial ossicles seated on the primary ossicles of the skeletal wall. Only smaller platelets and spinelets are known among somasteroids, although generally poor preservation limits knowledge. INTERPRETING THE SOMASTEROIDEA: ASPECTS OF LIFE MODE Somasteroid configurations are similar to those of extant asterozoans thereby favoring similar life habits, although apomorphies of the derived clades might favor major changes. Configuration of virgalia led Spencer (1951) to interpret the virgal field as indicating suspension-feeding habits using water currents with ciliary and tube foot activity to transfer particles toward the mouth; exhaust currents and rejected particles found “[…] outlet at the interradial angles (that were) devoid of skeleton” (p. 97). Posited interradial skeletal discontinuity, a “gap” or “cleft”, resulted in deeply petaloid arms (Spencer 1951; Spencer & Wright 1966). The arched type specimens of Villebrunaster (Fig. 9A; 10D) further led Spencer to envision arms upraised in life in accordance with a ciliary feeding mode while also living “partially under the bottom mud”. Seemingly challenging the interpretation of Villebrunaster, Chinianaster “specimens give little information as to mode of life” (p. 100). Living with food-collecting surfaces against the substrate was viewed with disfavor because the habit would “tend to choke” ciliary channels (Spencer 1951: 97). The “slightly built” somasteroid skeleton was envisioned as capable of considerable changes of form in a manner exemplified by earthworms. Abilities of other living organisms to construct reinforced supporting burrow walls also was noted (p. 93), somasteroid habits apparently seen in parallel. The skeletal flanges (Figs 7A, C; 8A, C, E) on the aboral mouth frame of Thoralaster are suggestive of exhaust passageways envisioned by Spencer (1951); the flanges, however, appear to be internal calling for any water exhaust passageways to be developed through the aboral body wall. More simply, the Thoralaster flanges might have served for gut confinement and support. Considerations of somasteroids in titles of Fell (e.g. Fell 1963a) were directed primarily toward that author’s phylogenetic interpretations, suspension-feeding crinoids treated as ancestral to somasteroids. Although retaining interpretations of ciliary feeding, Fell (1963a) accepted selective detrital feeding in extant Platasterias Gray, 1871, based on presence of small inferred prey at the mouth. Platasterias was assigned to the Somasteroidea but later recognized as a subgenus of the extant asteroid Luidia (Blake 1982). Interpretations of Spencer (1951) were later modified (Spencer & Wright 1966: 24). Ciliary activity was seen as serving to collect particles that fell “on or near” the somasteroid, and although no mention was made of somasteroid burrowing in Spencer & Wright (1966), reconstruction of an Ordovician ophiuroid with upraised arms was interpreted as having withdrawn into its burrow prior to its death (fig. 4). In contrast, somasteroids were envisioned as “amuscular […] relatively sedentary, dominantly epifaunal […] with deposit feeding […] primary” (Dean Shackleton 2005: 60), challenging ciliary feeding among somasteroids. The broadly stellate overall form of somasteroids similar to those of many asteroids suggests epifaunal habits with the oral surface directed toward the substrate. Although Spencer (1951) suggested at least semi-infaunal “burrows”, most fossil occurrences appear more or less restricted to single planes (e.g. Fig. 5C). The challenge of Spencer (1951) that virgalia directed toward the substrate would foul ciliary feeding can be answered either by an emphasis on selective detrital feeding or epifaunal lifting of the arms for ciliary feeding, as in brisingid asteroids and many extant ophiuroids. The number of specimens of Cantabrigiaster that have been offered for sale on the marketplace together with occurrence of as many as six closely adjacent specimens on a single block (Fig. 5C) favor local concentrations rather than only scattered occurrences. SYSTEMATIC PALEONTOLOGY recognition of AsterozoA Phylum-level expressions treated as plesiomorphic among asterozoans are presence of a water vascular system, approximate pentaradiate symmetry, and at least a precursor to a readily preserved stereom skeleton. Expressions either plesiomorphic at the subphylum level or subphylum apomorphies are essentially uniform pentamery of closely fitted mouth frames and proximal axials (i.e., absence of a so-called “buccal slit”), the actual presence of a readily preserved skeleton, ambulacra directed toward the substrate, and free-living epifaunal life modes. “Essentially” is uniformity of ambulacra around the mouth frame but not necessarily biologically important differentia that do not markedly alter overall uniformity, including but perhaps not limited to expression of Lovén’s Law, hydropore differentiation, and anal presence. As noted earlier, marked variability among so-called buccal slits identifies these as aberrancies of preservation. reMArk For reading convenience and clarity, diagnoses and the key to somasteroid taxa are comparative rather than compilations of inferred apomorphies.
463 Somasteroidea and early Asterozoa COMPTES RENDUS PALEVOL • 2025 • 24 (23) Class SOMASTEROIDEA Spencer, 1951 d iAgnosis . — Overall form low arched; outline ranging from subpentagonal with arms broad, more abruptly tapering, to outline substellate, arms triangular, elongate, more gradually tapering. Abactinals small, individually irregular but aboral surface in total uniform. Abactinals divisible into three types: abactinals delicate, multiradiate, arrangement reticulate; abactinals closely fitted small platelets; enlarged primary abactinals absent, ossicles limited to granules. Abactinals not aligned in rows, carinal, centrale, and aboral ring differentiation unknown. Madreporite recognized in three genera. Ambital frameworks varied, ranging from complexly arranged tiny platelets to single well-defined abutted series. Axial positioning across arm midline irregular, locally clearly offset to nearly opposite. Axials not permanently vaulted to form a furrow, but arm and disk capable of facultative flexure as to yield temporary furrow-like configurations. Axials nearly equidimensional, form differing among genera. Axial radial water vascular channel large, closed or nearly closed over water-vascular tissues in most genera. Transverse water-vascular channel ill-defined. Transverse ridge generally narrow, podial basins large, deep in most genera. Mouth frame ossicles relatively small, differentiation from more distal axials comparatively limited. Mouth-angle ossicles upright; small spinelets can occur; podial basin of adjacent axial aligned with those of more distal axials. Axillary (odontophore) not recognized. Terminal ossicle problematic, not definitively recognized. Linear, transverse series of proportionately small rod-like ossicles (“virgals”, the single series a “virgalium”, plural “virgalia”) radiate abradially from each axial, the first of the series more (e.g. Archegonaster) or less (e.g. Chinianaster) clearly differentiated from the remainder of the series. Virgalia occupy the interspace between ambital framework and axials thereby occupying the oral disk plane: actinal ossicles not recognized. Virgalium in life capable of some rotation about the longitudinal axis, virgalia capable of coordinated series deflection in the body plane. Virgalia thought to be lacking proximally from one genus. Accessories limited to relatively small spinelets and granules. Family chiniAnAsteridAe Spencer, 1951 Chinianasteridae Spencer, 1951: 93. key to the soMAsteroideA spencer, 1951 1. Axial ossicles “T”-shaped, forming enlarged gaps (podial pores?) between sequential transverse ridges. First virgals enlarged, strongly differentiated. Virgal series not recognized proximally. Ambital framework ossicles proportionately large, abutted, aligned in linear series. Abactinals are tiny granules ........................................ ..................................................................................................................... monogeneric Archegonasteridae — Axial ossicles square to weakly rectangular, few possible small podial pores recognized in two genera. First virgals at most weakly differentiated. Virgal series recognized proximally. Ambital framework ossicles small, otherwise varied. Abactinals are weakly enlarged spicules or platelets ........................ Chinianasteridae Spencer, 1951, 2 2. Overall form more nearly stellate, arms comparatively narrow. Ambital framework ossicles more robust, rodlike, elongate, overlapping but not irregular. Abactinals granular to plate-like, closely abutted, arrangement not reticulate .................................................................................... monogeneric, Ophioxenikosinae n. subfam. — Overall form more nearly polygonal, arms comparatively broad. Ambital framework ossicles less robust, granular to weakly elongate, arrangement more or less irregular. Abactinals rod-like, spicular, arrangement reticulate, not closely abutted ............................................................................................................................................. 3 3. In oral view, axials “L”-shaped, podial basin proximal of transverse ridge ....................................................... ..................................................................................................... 2 genera, Villebrunasterinae Fell, 1963b, 4 — In oral view, axial interval abradial to radial channel bilateral; podial basins approximately shared by successive podial basins ............................................................................. 3 genera, Chinianasterinae Spencer, 1951, 5 4. Abradial adaxials variously differentiated, arrangement varied ............................ Villebrunaster Spencer, 1951 — Abradial adaxials uniform, arrangement uniform ...................................................... Ampullaster Fell, 1963b 5. Axials in aboral aspect shield-like and clearly overlapping distally, compound axials unknown. Abactinals comparatively less delicate. Madreporite where recognized on oral surface near but not abutting mouth frame. Ambital framework of many tiny platelets forming a complex apparently somewhat ill-defined series. Virgals moderately robust, rectangular; medial ridge lacking. Adjacent virgalia potentially forming a robust platform when deflected distally. “Radioles” not developed .................................................. Chinianaster Thoral, 1935 — Axials in aboral aspect approximately square in outline and weakly overlapping distally, compound axial known only at mouth frame. Abactinals comparatively more delicate. Madreporite where recognized on aboral surface away from central disk. Ambital framework ossicles numerous, small but not tiny, forming a complex well-defined series. Virgals stout, rectangular, with a medial ridge. Adjacent virgalia forming a platform with well-defined grooving shared by adjacent virgalia. “Radioles” not developed ...................................................................... ....................................................................................... Cantabrigiaster Hunter & Ortega-Hernández, 2021 — Axials in aboral aspect approximately square in outline, at most weakly overlapping distally, compound axials can be developed at least near mouth frame. Abactinals comparatively more delicate. Madreporite not recognized. Ambital framework ossicles of many tiny platelets forming a complex apparently somewhat ill-defined series. Virgals very delicate, grooved, rodlike. Adjacent virgalia too slender to form a platform. An enlarged attenuated “radiole” can occur at the abradial termini of abutted virgalia ................... Thoralaster Dean Shackleton, 2005
464 COMPTES RENDUS PALEVOL • 2025 • 24 (23) Blake D. B. & Lefebvre B. Chinianasteridae restricted to Chinianaster Fell, 1963b: 144; Spencer & Wright 1966: 39. Chinianasteridae included Villebrunaster, Chinianaster, Thoralaster, Ophioxenikos: Dean Shackleton 2005: 30. type genus. — Chinianaster Thoral, 1935. type species. — Chinianaster levyi Thoral, 1935. diAgnosis. — Abactinal skeleton well-developed, consisting of many small, irregular but uniform ossicles. Ambital framework varied among genera, ossicles proportionately small, series well defined but ossicular arrangement irregular, varying among genera. Axials approximately equidimensional to rectangular; localized podial pores possibly occurring in two genera. Water-vascular channel skeletally closed orally. Virgalia reaching mouth frame. First virgal at most weakly differentiated. Subfamily chiniAnAsterinAe Spencer, 1951 Chinianasteridae Spencer, 1951, here recognized at the subfamily level for Chinianaster, Cantabrigiaster, and Thoralaster. type genus. — Chinianaster Thoral, 1935. type species. — Chinianaster levyi Thoral, 1935. diAgnosis. — Subpentagonal Chinianasteridae. Abactinals spiculate, arrangement reticulate. Ambital framework ossicles tiny, granular or plate-like; overall arrangement thought irregular. Radial water vascular canal large, skeletally delicate, closed orally, where closure was diagenetically lost abradial portion of ossicle doubly bilateral at midpoint of transverse ridge. Podial basin boundary approximately medial, basin shared equally by successive axials. Adradial adaxials weakly differentiated, virgalia relatively elongate. Genus Chinianaster Thoral, 1935 Chinianaster Thoral, 1935: 127. diAgnosis. — As for Chinianaster levyi, the type and only recognized species. Chinianaster levyi Thoral, 1935 (Figs 1A; 2; 3) Chinianaster levyi Thoral, 1935: 127, pl. 9, fig. 1a, 1b; non pl. 8, fig. 1; non pl. 10, fig. 4. — Spencer 1951: 98, pl. 3, figs 35, 36, textfigs 7, 8, non pl.2, figs 32, 33. — Ubaghs 1953: 814, text fig. 17. — Fell 1963a: pars 393-403, fig. 8B, non 6E. — Spencer & Wright 1966: U39, figs 8.2, 13, 19.1, 39.4. — Blake 1982: fig. 1E, non fig. 1C. — Dean Shackleton 2005: 68, pl. 3, figs 3, 4, text figs 5, 12B. — Blake 2013: 363, figs 1.1, 1.2. — Blake & Guensburg 2015: 467, figs 1.1-1.6, 2.1-2.7, 3.1-3.4. — Blake 2018: 2, 21; pl. 1.1, 1.2, fig. 2.1. — Blake 2024: 2 et seq., pl. 2.1-2.3. type MAteriAl. — Lectotype. France • 1 specimen (specimen distorted, arm radii approximately 25 to 30 mm); Hérault, Saint-Chinian; SaintChinian Formation; Euloma filacovi Zone, late Tremadocian (Early Ordovician); Villebrun leg.; UCBL-FSL 168691 (Figs 2A1-4; 3A). referred speciMens. — Eight specimens (UCBL-FSL 711093 [FSL 1879 553 of Dean Shackleton 2005], UCBL-FSL 711094 [FSL 1879 558 of Dean Shackleton 2005], UCBL-FSL 711095 [FSL 1879 563 of Dean Shackleton 2005], UCBL-FSL 712002712004, UCBL-FSL 712090, UCBL-FSL 713577. Questionable, four more specimens (MBB-GG20, MBB-GG23, UCBL-FSL 712017, UCBL-FSL 713576). Assignment of two more specimens is problematic (MBB-GG2, MBB-GG18). type locAlity And horizon. — Saint-Chinian Formation, Early Ordovician (late Tremadocian); Saint-Chinian (Hérault), Montagne Noire, France. d iAgnosis . — Abactinals moderately robust, arrangement quite closely reticular (Fig. 2A). Ambital framework ossicles tiny, plate-like; arrangement complex, series as preserved ill-defined, irregular (Fig. 2BD). Axials in aboral view shield-like, successive axials overlapping (Fig. 2A). In oral view, compound axials not recognized. MAO not bearing an enlarged flange-like aboral process. Where not eroded, radial-water vascular channel enclosed at arm axis by an enclosing skeletal arch (Figs 2C, E; 3B, E). Adaxials moderately large, thin, broad surface longitudinally grooved, groove broad (Figs 2E; 3C). description Overall form in life low-arched, outline subpentagonal; arms broad, triangular, taper gradual. Abactinals spiculate, multiradiate, rod-like abactinals likely developed; abactinal arrangement open hexagonal reticular. Madreporite on oral surface offset from MAO, surface texture granular (Figs 2C; 3A, B). Ambital framework a continuous well-defined but irregular necklace of tiny platelets; ambital framework not deflected toward mouth frame to form a gap or cleft (Fig. 2B-D). In aboral aspect, axials shield-like, surface curved, sequential axials overlapping, axial series longitudinally grooved approximately at position of abradial margin of podial basins; proximal axials with possible podial pore (Fig. 2A, F). In oral aspect, where preserved (generally distally), radial water-vascular channel oral surface closed by shield-like skeletal arch (Figs 2C, E; 3B); where shield eroded (generally proximally) and axial series dilated, axials appearing approximately double-bilateral along and normal to transverse ridge; podial basin boundary medial; abradial margin concave. MAO proportionately small, appearing plate-like where directed toward mouth, rounded where deflected toward interior; lateral margins concave for tube foot; differentiation of circumoral appearing limited (Fig. 3E). Virgalia abutting abradial terminus of axial transverse ridge, virgalia reaching mouth frame (Figs 2B; 3B, C, E). Virgals relatively thin, rectangular, planar, grooved, termini expanded; virgals when rotated to exposed broad surface potentially robust enough as to have formed a continuous platform at least where deflected distally. First virgals less elongate than more lateral virgals, otherwise similar. Virgal accessories, if any, small, granular. reMArks The concept of Thoralaster Dean Shackleton 2005, was based on a part of the Chinianaster type suite, see under that genus. Shield-like overlapping axials and flat, rectangular adaxials provide guides to the recognition of Chinianaster. Although uncommonly clearly preserved, an ambital framework of fine platelets is shared only with Thoralaster. Dean Shackleton (2005: 68R), however, posited presence of robust marginals in Chinianaster, some a “large spike”. The interpretation
465 Somasteroidea and early Asterozoa COMPTES RENDUS PALEVOL • 2025 • 24 (23) fig. 2 . — Chinianaster levyi Thoral, 1935 Saint-Chinian Formation, Early Ordovician (late Tremadocian); Montagne Noire, France; latex casts: A-D, lectotype UCBL-FSL 168691 (Villebrun collection), Saint-Chinian (Hérault): A, aboral view; abactinal configuration to left is hexagonal reticulate; some axials “C”-shaped with possible podial pores that are aligned with longitudinal grooving of axial series; flange-like series of unknown origin but suggestive of deflected adaxials, the “intervirgal struts” (Dean Shackleton 2005) postulated for Villebrunaster Spencer, 1951; B, area to right of C, ambital necklace (an) of fine ossicles, homologous with robust marginals of many more derived asterozoans; C, oral view, the proximal intervals of the ambulacra and mouth angle ossicles (MAO) were widely distended by sediment compaction, the virgalia to right pulled away from the axials; axials where not deflected are approximately bilateral at transverse ridge; madreporite; D, area to right of B, virgalia rotated to expose edges, details of the ambital necklace; E, F, UCBL-FSL 712003 (Vizcaïno collection), Félines-Minervois (Hérault): E, oral view, axials remain closed by oral shields more distally but in ambulacrum to right, proximal axial series distended and eroded; virgalia disrupted but reaching oral frame; F, aboral view, photograph of distal arm, see reconstruction of Dean Shackleton (2005: fig. 5B); inflections suggesting gaps or possible podial pores; small ossicles fringing the arm suggest adaxials and remnant ambital framework platelets; large spinelet, a possible terminal (ter?). Abbreviations: fl, flange-like series; lg, longitudinal grooving; mad, madreporite; pp?, possible podial pores; vir, virgalia. Scale bars: A-C, 5 mm; D-F, 3 mm. pp? lg MAO an an fl mad vir an mao vir an an pp? ter? A C B D E F
466 COMPTES RENDUS PALEVOL • 2025 • 24 (23) Blake D. B. & Lefebvre B. appears to have been based on her figure 5B (p. 40), the apparent interval illustrated here (Fig. 2F) in which ossicles are displaced and enlarged “spikes” are found at the arm tip. Spike identity is uncertain but more proximal ossicles argue terminal ossicles of virgalia, the ambital necklace all but lost from this specimen (Fig. 2F). A single ossicle at the arm tip of a Chinianaster or near-Chinianaster specimen (Fig. 14H) suggests a spike-like terminal. Dean Shackleton (2005) interpreted virgalia as lacking at the mouth frame of Chinianaster; although largely disrupted, remnants of virgalia are common, including in the lectotype (Fig. 2C, D). Genus Cantabrigiaster Hunter & Ortega-Hernández, 2021 Cantabrigiaster Hunter & Ortega-Hernández, 2021: 2. Villebrunaster Blake & Hotchkiss, 2022: 30. type species. — Cantabrigiaster fezouataensis Hunter & OrtegaHernández, 2021. diAgnosis. — As for Cantabrigiaster fezouataensis, the type and only recognized species. Cantabrigiaster fezouataensis Hunter & Ortega-Hernández, 2021 (Figs 4; 5) Cantabrigiaster fezouataensis Hunter & Ortega-Hernández, 2021: 2, fig. 1; electronic supplemental material. Villebrunaster fezouataensis — Blake & Hotchkiss 2022: 29, figs 2-5. type MAteriAl. — Holotype. Morocco • 1 specimen (only oral surface, good preservation of ossicular detail; arm radius R 27 mm; disk radius r 18 mm; both measurements and especially that of the latter extended by sediment compaction); Central Anti-Atlas, fig. 3. — Chinianaster levyi Thoral, 1935 Thoral, Saint-Chinian Formation, Early Ordovician (late Tremadocian); Montagne Noire, France; latex casts: A, lectotype UCBL-FSL 168691 (Villebrun collection), Saint-Chinian (Hérault); madreporite, the granular surface and ridged margin unlike madreporites of most asterozoans; B, UCBL-FSL 712002 (Vizcaïno collection), Félines-Minervois (Hérault); oral view, mouth angle ossicles pair, proximal axials distended, more distal approximate life positioning; madreporite with disrupted near-oral virgalia and abactinals; C, UCBL-FSL 713577 (Vizcaïno collection), FélinesMinervois (Hérault); oral view, specimen in bud-like posture; axials distended; podial basins equally shared by successive axials; unlike those of Figure 2, virgalia largely show broad surfaces, those to right largely in place, those to left disrupted but reaching mouth frame area; D-F, UCBL-FSL 712004 (Vizcaïno collection), Félines-Minervois (Hérault); D, aboral view, axial surfaces arched; spike-like ossicles of uncertain origin at arm tip; E, F, oral views, F, mouth frame ossicles to left of E, mouth angle ossicles retain well-defined curvature for podium; for orientation analogy, see Figure 4; axial remnant. Abbreviations: ax, axial; mad, madreporite; MAO, mouth angle ossicles. Scale bars: A, F, 1 mm; B, D, E, 5 mm; C, 3 mm. ABC DE F mad MAO ax ax MAO ax ax MAO
467 Somasteroidea and early Asterozoa COMPTES RENDUS PALEVOL • 2025 • 24 (23) fig. 4. — Cantabrigiaster fezouataensis Hunter & Ortega-Hernández, 2021 Fezouata Formation, Early Ordovician (late Tremadocian); Central Anti-Atlas, Morocco; latex casts: A-D, holotype UCBL-FSL 424961 (Van Roy collection), Ternata plain, N of Zagora: A, oral view of specimen remainder; adaxials approximately in life configuration near arm tips, largely lost diagenetically in interbrachia; mouth angle ossicles, arrows correspond with D; marginals; B, arm to lower left of A, axials with adaxial virgals abutted to form a platform, axial positioning across midline irregular, both paired and offset; C, A rotated clockwise, a single adaxial first virgal abuts the two proximal axials; compound axial; podial basins of proximal axials to right appear inclined toward mouth angle ossicles although this might reflect preservation rather than life configuration; B, C and D are separate latex casts differing in expression of details of mouth angle ossicles; first virgal and compound axial of C and D correspond; mouth angle ossicles pair fortuitously differ in orientation, pair to right in inferred at life rest position, with faint accessory bases; pair to left with mouth angle ossicles rotated in inferred feeding position as to direct particulates into disk; E, paratype UCBL-FSL 711938 (Lefebvre collection), Jbel Tizagzaouine, c. 21 km N of Zagora; specimen in bud-like posture, mouth frame obscure, two dilated ambulacra, tips obscured by marginals; virgalia forming a platform distally; a single virgalium (vir) extends from mouth frame thereby demonstrating absence of an interradial “gap” or “cleft”; F, paratype UCBL-FSL 711939 (Lefebvre collection); Jbel Tizagzaouine, c. 21 km N of Zagora; aboral view, abactinal form and arrangement, aboral surface of arm largely lost, part of ambital framework remains. Abbreviations: cax, compound axial; mar, marginals; MAO, mouth angle ossicles; v1, fisrt virgal. Scale bars: A, 10 mm; B-F, 5 mm. AB C D EF MAO mar v1 cax v1 cax MAO vir
468 COMPTES RENDUS PALEVOL • 2025 • 24 (23) Blake D. B. & Lefebvre B. fig. 5. — Cantabrigiaster fezouataensis Hunter & Ortega-Hernández, 2021 Fezouata Formation, Early Ordovician (late Tremadocian); Jbel Kissane, c. 5 km E of Agdz, Central Anti-Atlas, Morocco; C is the original specimen, the remainder are latex casts: A, B, PRIP 20029-1 (Blake collection), aboral view: A, overall aboral view; distal left axials slightly pulled apart; radiating virgalia dominate distally on arms; some abactinals remain at interbrachia; madreporite and some marginals remain; B, madreporite granular surface (upper right) suggestive of that of Chinianaster Thoral, 1935, see Figure 3; offset of axial series suggests madreporite displacement from life position; C, PRIP 20028-1 – 20028-6 (Blake collection), six individuals on a single slab, medial and lower right specimens in aboral view, remainder in oral view. The slab is 10 mm to 15 mm in thickness and shows no clear indication of depositional discontinuity. The surface of the block was reworked in preparation but appears homogeneous. The specimen to far left is separated from the adjacent by a 1-2 mm sediment band, that to upper right by about 5 mm; D, PRIP 20029-2 (Blake collection), oral view; disk, proximal arms distended to show axial aboral surfaces; marginals remain locally; abactinals exposed in interbrachia; radiating virgalia form a platform distally; E, PRIP 20030-1 (Blake collection), oral view, axial form, series closing distally, adaxials toward tip disrupted, many marginals remain, abactinals at interbrachium. Abbreviations: mad, madreporite; mar, marginals. Scale bars: A, D, E, 5 mm; B, 2 mm; C, 50 mm. AB C DE mad mar mar mar
469 Somasteroidea and early Asterozoa COMPTES RENDUS PALEVOL • 2025 • 24 (23) Ternata plain (north of Zagora); Sagenograptus murrayi Zone, late Tremadocian (Early Ordovician); 2003, Van Roy leg.; UCBLFSL 424961 (Fig. 4A-D). referred speciMens. — 34 specimens (MHNN.P.045596, PRIP 20026-20027, PRIP 20028.1-6; PRIP 20029.1-2, PRIP 20030.12, UCBL-FSL 424962, UCBL-FSL 711937-711939, UCBLFSL 711945-711946, YPM IP 535545-535559). t ype locAlity And horizon . — Fezouata Formation, Early Ordovician (late Tremadocian); Ternata plain, Zagora area, AntiAtlas, Morocco. diAgnosis. — Abactinal arrangement open reticular (Figs 4F; 5A, C, D). Ambital framework ossicles small, granular, complexly overlapping but closely abutted as to form a clearly defined series (Figs 4E; 5A, D, E). Axials in aboral view rectangular, successive axials abutted, not notably overlapping (Fig. 5A). In oral view, compound axials can occur at mouth frame (Fig. 4C). Radial water-vascular channel narrowly enclosed at arm axis (Figs 4A, C; 5A). Adaxials strongly robust, rectangular, longitudinal ridges well-defined, adjacent abutted virgalia forming a transverse welldefined groove, abutted virgalia forming a distinct platform (Figs 4A, B; 5D, E). description Overall form in life low-arched, outline subpentagonal; arms broad, short, triangular. Abactinals rod-like; multiradiate abactinals not identified. Only identified madreporite (Fig. 5A, B) aboral, surface texture granular, madreporite offset from central area of disk. Ambital framework well-defined, marginal series forming a continuous pentagonal outline extending around the arm tip, series not deflected toward mouth frame to form gap or cleft. Ambital framework ossicles small, numerous, equidimensional, granular to weakly elongate; ossicles overlapping, not differentiated as to suggest inferomarginals and superomarginals. In aboral aspect, axials nearly paired or slightly offset across arm midline, axial outline nearly square, sequential axials abutted; axial series (only where better preserved?) appearing longitudinally grooved. In oral aspect, axial outline approximately rectangular, water vascular channel large, enclosed. Axial transverse ridge narrow, axial approximately doubly bilateral at midpoint of transverse ridge, podial basin large, equally shared by subsequent axials, transverse ridge flared abradially to form concave seat for virgalium. Compound axial can occur at mouth frame. Terminal not recognized. First virgals smaller than but similar to more abradial; all virgals robust, rectangular, bearing a medial ridge and lateral groove shared by adjacent virgalia, ossicular boundaries approximately medial in groove. As typically preserved, adjacent virgalia deflected distally as to form a pavement. Accessories not clearly identified, some circular pustules and circular depressions might favor accessories. reMArks A posited absence of an ambital framework was foundational to the recognition of Cantabrigiaster fezouataensis, and putative absence essential to Cantabrigiaster assignment to a basal position within Somasteroidea. Presence of an ambital framework similar to that of Villebrunaster was documented in the holotype and other specimens of the type suite, and with emphasis on the framework, Cantabrigiaster was synonymized with Villebrunaster (Blake & Hotchkiss 2022). Herein, axial and adaxial expressions are argued as providing essential guides to asterozoan affinities (e.g. Blake 2013, 2018, 2024; Blake & Guensburg 2015; Glass etal. 2024), the differences between Cantabrigiaster and other somasteroids calling for generic recognition. Most distinctive, the robust adaxials of Cantabrigiaster differ from those of other somasteroid genera in both form and arrangement, with adjacent virgalia abutted laterally to form a robust platform. The ambital framework of Cantabrigiaster differs from those of Chinianaster, Villebrunaster, and Ampullaster in ossicular shape but not in overall series configuration. Surface texture of the madreporite (Fig. 5A, B) is similar to that of Chinianaster (Fig. 3A, B) although the two differ in madreporite positioning. Axial series offset and disruption of more proximal abactinals of the only Cantabrigiaster example exhibiting a madreporite indicate some displacement accompanied preservation, the present positioning therefore of unknown general significance. Genus Thoralaster Dean Shackleton, 2005 Thoralaster Dean Shackleton 2005: 68. type species. — Thoralaster spiculiformis Dean Shackleton, 2005. diAgnosis. — As for Thoralaster spiculiformis, the type and only recognized species. Thoralaster spiculiformis Dean Shackleton, 2005 (Figs 1B; 6-8) Chinianaster levyi Thoral, 1935, pl. 8, fig.1. — Spencer 1951: pl. 2.32, 2.33.— Fell 1963a: fig. 6E. — Blake 1982: fig. 4C. Thoralaster spiculiformis Dean Shackleton, 2005: 68, pl, 4.1-4.6, fig. 7. — Blake 2013: fig. 1.6. — Blake & Guensburg 2015: 472, figs 5.1-5.5, 6.1-6.8. t ype MAteriAl . — Holotype. France • 1 specimen (part and counterpart); Hérault, Saint-Chinian, La Croix-Rouge; Euloma filacovi Zone, late Tremadocian (Early Ordovician); 1953, Thoral leg.; UCBL-FSL 168697 (“ES1” of Dean Shackleton 2005); (Fig. 6A1-6). Paratype. France • 1 specimen; Hérault, Saint-Chinian; Euloma filacovi Zone, late Tremadocian (Early Ordovician); 1879, Lignières leg.; UCBL-FSL 711096 (“FSL 1879 564” of Dean Shackleton 2005) (Fig. 7B). referred speciMens. — Five specimens (UCBL-FSL 168690, UCBL-FSL 424943, UCBL-FSL 712005, MNHN.F.A90271, MNHN.F.A97739). type locAlity And horizon. — Saint-Chinian Formation, Early Ordovician (late Tremadocian); La Croix-Rouge, E of Saint-Chinian (Hérault), Montagne Noire, France.
470 COMPTES RENDUS PALEVOL • 2025 • 24 (23) Blake D. B. & Lefebvre B. diAgnosis. — Abactinals delicate, arrangement open reticular (Fig. 7A-C). Ambital framework ossicles tiny, plate-like, arrangement complex, series as preserved ill-defined, irregular (Figs 6D-F; 7A, C, E, F). Radial-water vascular channel narrowly enclosed at arm axis (Fig. 8D, distal). In oral view, compound axials recognized near mouth frame (Figs 1B; 6A-C; 8D). MAO bearing an enlarged flange-like aboral process (Figs 7A, C; 8A, C, E). Adaxials very delicate, rodlike, longitudinal groove narrow (Figs 1B; 6B, F; 7A, C; 8B). fig. 6. — Thoralaster spiculiformis Dean Shackleton, 2005 Saint-Chinian Formation, Early Ordovician (late Tremadocian); Saint-Chinian (Hérault), Montagne Noire, France; latex casts, holotype UCBL-FSL 168697 (Thoral collection): A-E, oral views: A, most of remnant; mouth frame distended, closure in life likely yielded a sub-stellate overall shape; arm midline corresponds with C, E; remnants of virgalium at mouth frame, mouth angle ossicles appearing blunt, rounded; B, upper left area of A, corresponds with Dean Shackleton (2005: fig. 7, here Figure 1B and rotated counter-clockwise); C, arm midline, dilated aboral surface of water vascular channel, corresponds with A and E; delicate, grooved virgals; compound axials; D, area to upper right of A; virgalia delicate as is typical of Thoralaster Dean Shackleton, 2005; ambital necklace remnants; virgals bear longitudinal grooves; virgalia extend to enlarged attenuated terminal radioles; ambital framework locally largely lost; E, arm midline corresponds with A and C; possible tube foot remnants to upper right; disrupted ambital framework (facing ambital necklace) extending transversely between virgalia and appearing adradial to terminal virgals; F, aboral view; axial series below, virgalia ambital framework disrupted; abutted virgalia with terminal attenuated? virgal, which is the “radiole” in terminology od Fell (1963a) radioles; positioning of medial radiole might suggest articulation sensu H.B. Fell; virgal accessories remain with medial virgalium. Abbreviations: am, arm midline; an, ambital necklace; cax, compound axials; DS, refer to identifications of Dean Shackleton (2005) of Figure 1B; dssm, DS “spiked marginals”, here “radiole”; dscp, DS “intervirgal cover plates”; dsv, DS “v1, ?ad”; some axials to lower left are compound; dsa2, DS ?amb2; MAO, mouth angle ossicles; rad, radioles; v, virgals; vir, virgalium. Scale bars: A, 10 mm; B-F, 5 mm. am MAO vir dssm dscp dsa2 dsv am cax v v v v an rad rad af an am an AB CD E F
471 Somasteroidea and early Asterozoa COMPTES RENDUS PALEVOL • 2025 • 24 (23) description Overall form low-arched, outline substellate, arm outline in life thought to be triangular, moderately abruptly tapering. Abactinals delicate, spiculate, configuration open hexagonal reticular. Madreporite unknown. Ambital framework forming a continuous, well-defined, irregular necklace of tiny platelets, series not deflected toward mouth frame to form a gap or cleft. In aboral aspect, axial ossicles shield-like, sequential ossicles weakly overlapping (Figs 6F; 7A-C; 8A, C, E), axial series longitudinally weakly grooved (Fig. 8A). In oral aspect, radial water vascular channel closed (near arm tips, Figs 6A; 7A; 8D, F). Some axials compound, i.e., bearing more than a portion of a podial basin on each side of the transverse ridge (Figs 1B; 6A, C; 8D); non-compound axials appearing approximately double-bilateral along and normal to the transverse ridge; podial basin boundary medial, abradial axial margin concave. Mouth-angle ossicle transverse ridges converge abradially in an “A”-frame-like pattern (Fig. 8D). Ossicle immediately fig. 7. — Thoralaster spiculiformis Dean Shackleton, 2005, Saint-Chinian Formation, Early Ordovician (late Tremadocian); Montagne Noire, France; latex casts: A-C, E, F, UCBL-FSL 712005 (Vizcaïno collection), Caunes-Minervois (Aude): A-C, aboral views: A, most of specimen fragment, axials converging toward arm tip to left, virgalia above, jaw frame to right with reticulated abactinal remnants; B, distal arm interval, very delicate abactinals retain reticulate life arrangement; C, right side of A, flared mouth frame suggestive of an open bivalve, skeletal discontinuity might indicate presence of both the mouth angle ossicle and a circumoral; D, paratype UCBL-FSL 711096 (Lignières collection), Saint-Chinian (Hérault); oral view, disk dilated; mouth angle ossicles pair at middle rounded bluntly toward mouth area; proximal-most axials little differentiated; virgalia remnants adjacent to mouth frame document absence of interradial “gap” or “cleft”; E, F, oral views, aboral surfaces of water-vascular channels lost, axials bilateral at transverse ridge, podial basins large; virgalia appearing locally to extend beyond ambital necklace; mouth angle ossicles and first podial basin aligned with subsequent basin, proximal axials not appearing differentiated. Abbreviations: an, ambital necklace; MAO, mouth angle ossicles; sd, skeletal discontinuity. Scale bars: A, C, E, F, 5 mm; B, D, 3 mm. sd an MAO an A C B D E F
478 COMPTES RENDUS PALEVOL • 2025 • 24 (23) Blake D. B. & Lefebvre B. fig. 12. — Villebrunaster thorali Spencer, 1951, Saint-Chinian Formation, Early Ordovician (late Tremadocian); Saint-Chinian (Hérault), Montagne Noire, France, UCBL-FSL 711092 (Lignières collection). The drawings, figures A, C, and E are reconstructions of Dean Shackleton (2005), these accurate enough as to allow corresponding photo documentation, B, D, and F. A is reversed in the reconstruction from the photograph of B but C is not reversed, see D. In the Dean Shackleton reconstruction, ambulacral, here axial is used. B, skeletal discontinuities to right of axials are suggestive of the embedded virgal configuration of stenuroids, their significance here uncertain but part of the complexities of the adradial virgalia of Villebrunaster; E, F, aboral views; axials, abactinals, and marginals are clearly exposed; neither a carinal series nor a terminal is recognized. Remaining abbreviations of Dean Shackleton (2005). Abreviations: amb, ambulacral; ax, axial; b, podial basin; iv, intervirgal struts; sk, skeletal discontinuities; v1, first virgals; v2, intervirgal struts. Scale bars: B, F, 3 mm; D, 1 mm. AB CD EF marginals v1 v2 ?ad ?ad amb intermediate virginals v2 iv v1 b amb marginals amb abactinal rods abactinal tripartite mega-paxillae Underlying virginals rows sk v1 iv v2 v2 iv v1 bamb
479 Somasteroidea and early Asterozoa COMPTES RENDUS PALEVOL • 2025 • 24 (23) fig. 13. — Ampullaster ubaghsi Fell, 1963b, UCBL-FSL-168673 (Villebrun collection), holotype and only recognized specimen, oral view, Saint-Chinian Formation, Early Ordovician (late Tremadocian); Saint-Chinian (Hérault), Montagne Noire, France: A, specimen remnant; B, enlargement of upper right; the proximal interval of the ambulacrum to right was slightly distended, other ambulacra lifelike. Axials across the arm midline are offset distally, but more nearly paired proximally, here considered an ontogenetic realignment retained phylogenetically within Asterozoa. Sediment compaction pushed some abactinals to the oral surface. Virgalia reach the mouth frame. Virgals toward the top of the image appear slender whereas those to the lower right suggest broader surfaces, these perhaps differentially rotated. A terminal is not recognized. Marginal form is not clearly expressed but appears more irregular than typical of Villebrunaster Spencer, 1951; C, D, two copies using different casting materials, D an unnumbered NHM cast of W.K. Spencer. Arrows correspond. First virgals ossicles are uniform, rectangular, possibly with lip-like shelves bordering the podial basins, these the “intervirgal struts” of Dean Shackleton (2005) and fundamental to the proposed synonymizing of Ampullaster Fell, 1963b with Villebrunaster. The interpretation here is that expressions differ enough to retain the generic concept of Ampullaster. Scale bars: A, 10 mm; B-D, 5 mm. AB C D
480 COMPTES RENDUS PALEVOL • 2025 • 24 (23) Blake D. B. & Lefebvre B. In the original diagnosis of Fell (1963b), marginal series were interpreted as edging deep interradial “V”-shaped “clefts” that produced petaloid arm outlines. It is argued here that the ambital framework was continuous across the interbrachium, as in all somasteroids. Fell (1963b) envisioned presence of gradational changes of axial expression along the length of the arm of Ampullaster, the most important the presence of skeletal discontinuities interpreted as podial pores. The interpretation is not accepted here. Subfamily ophioxenikosinAe n. subfam. urn:lsid:zoobank.org:act:FDF53B0D-66B0-46B5-A22A-B60C7C4BB7CD type genus. — Ophioxenikos Blake & Guensburg, 1993. d iAgnosis . — Substellate Chinianasteridae. Abactinals granular to plate-like, closely appressed. Ambital framework ossicles moderately elongate, aligned, weakly overlapping. Radial water-vascular channel small; skeletally closed. Podial basin boundary approximately medial, basin shared equally by successive axials. Adradial adaxials weakly differentiated, virgalia relatively short. reMArks For purposes of comparison, the diagnosis is written in parallel with those for the Chinianasterinae and Villebrunasterinae. The Ophioxenikosinae n. subfam. is known only from O. langenheimi; the diagnosis applies at the species level. Genus Ophioxenikos Blake & Guensburg, 1993 Ophioxenikos langenheimi Blake & Guensburg, 1993 starfish Byrd, 1970: 29, fig. 5. Ophioxenikos langenheimi Blake & Guensburg, 1993: 109, figs 2.1-2.3, 2.5, 3. — Dean Shackleton 2005: 71, pl. 3.5. — Blake & Guensburg 2015: 470, fig. 4.1. type MAteriAl. — Holotype. United States • 1 specimen; southcentral Nevada, Ely Springs Mountain Range; Lower Pogonip Group, late early to middle Floian (Early Ordovician); PRIP UI X-4751. type locAlity And horizon. — Lower Pogonip Group, Early Ordovician (late early to middle Floian); Ely Springs Mountain Range, south-central Nevada, United States. description Overall form in life low-arched, outline substellate; arm outline in life triangular, quite abruptly tapering. Abactinals irregular, abutted, small, granular to plate-like. Madreporite unknown. Ambital framework well-defined, series forming a continuous outline extending around the arm tip, not deflected toward the mouth frame; marginals rod-like, robust, overlapping, alignment irregular to regular; accessory faceting not recognized. Axials approximately equidimensional, aboral appearance unknown; in oral aspect, radial water-vascular channel enclosed, small, tubular. Axials approximately bilateral both along and perpendicular to transverse ridge; podial basin shared by sequential axials; compound axials not recognized. Mouth frame ossicles small, appearing little differentiated from more distal ossicles; mouth-angle ossicles rectangular. First virgal short, otherwise similar to more lateral virgals. Abradial virgals somewhat enlarged irregular to cylindrical, rod shaped. Any accessories unknown. reMArks The differing preservational styles of Ophioxenikos and the French-Moroccan genera render comparisons difficult. Floian Ophioxenikos is younger than Tremadocian Cantabrigiaster and the Saint Chinian genera but older than Middle Ordovician Archegonaster. Family ArchegonAsteridAe Spencer, 1951 Archegonasteridae Spencer, 1951: 101. type genus. — Archegonaster Jaekel, 1923. diAgnosis. — Abactinal skeleton limited to tiny granules. Ambital framework ossicles proportionately large, angular, forming a linear sequence. Axials “T”-shaped, gaps between successive axials suggesting podial pores. Water-vascular channel not skeletally closed orally. Virgalia not known to reach mouth frame. First virgal strongly differentiated. reMArks For purposes of comparison, the diagnosis is written in parallel with that for the Chinianasteridae. The Archegonasteridae is known only from A. pentagonus; the diagnosis applies at the species level. Genus Archegonaster Jaekel, 1923 Archegonaster pentagonus Spencer, 1951 Archegonaster pentagonus Spencer, 1951: 101, pl. 2, fig. 34; pl. 3, figs 37, 38; pl. 4, figs 39, 40; text-figs 9, 10, 12-15. — Ubaghs 1953: fig. 18. — Fell 1963c: 463, fig. 5I. — Spencer & Wright 1966: 41, fig. 39.3. — Smith & Jell 1990): 753, fig. 37-51. — Dean Shackleton 2005: 64, pl. 3.2, fig. 12a. — Blake & Guensburg 2015: 477, fig. 4.2. — Villier etal. 2018: 404. t ype MAteriAl . — Holotype. Czech Republic • 1 specimen; Prague Basin, Osek; Šárka Formation, Darriwilian (Middle Ordovician); NMP L10143 (part) and NMP L10144 (counterpart). referred speciMens. — Reviewed from the literature (see Smith & Jell 1990; Dean Shackleton 2005). type locAlity And horizon. — Šarká Formation (Llanvirn), close to Ošek, Prague Basin, Czech Republic. description Somasteroid in life low-arched, outline pentagonal. Aboral skeleton limited to granules. Madreporite aboral, surface
481 Somasteroidea and early Asterozoa COMPTES RENDUS PALEVOL • 2025 • 24 (23) of radiating ridges and grooves. Ambital framework welldefined, marginals robust. Axials “T”-shaped, overlapping, with a large opening, an apparent podial pore. First adaxials strongly differentiated, more lateral adaxials proportionately small, rod-like. Proximal virgalia not recognized. reMArks The Jaekel (1923) treatment of Archegonaster was cursory, the specific name later designated from a Jaekel manuscript (Spencer 1951: 101). Morphology was reviewed in detail by Spencer (1951), Smith & Jell (1990), and Dean Shackleton (2005). fig. 14. — Many specimens of the French/Moroccan asterozoan specimen suite are not complete enough to assign at lower taxonomic levels: select examples are illustrated: A, B, C, asterozoans too poorly preserved to be assigned at the class level; UCBL-FSL 712046 (Reboul collection); Fezouata Formation, Early Ordovician (early Floian); Toumiat, c. 17 km NE of Zagora, Central Anti-Atlas, Morocco. Two of three individuals together on a small slab, the early Floian age making them among the oldest-known asterozoans: A, B, both surfaces of one specimen, aboral vs oral difficult to determine; arm midlines suggest axials; smaller ossicles are suggestive of somasteroid abactinals and virgals. The central disk appears filled with sediment suggesting substrate rather than suspension feeding; C, disk distortion suggests compaction around sediment and substrate feeding rather than differentiation of disk ossicles; D, Somasteroidea Spencer, 1951 indeterminate, AA.BCBb.OI.36 (Lefebvre collection); Fezouata Formation, Early Ordovician (middle Floian), Bou Chrebeb, c. 27 km NE of Zagora, Central Anti-Atlas, Morocco. Oral view, dilated ambulacral column converges distally to left; axial form suggestive of those of Chinianaster Thoral, 1935, small, rodlike virgals and irregular elongate overlapping marginals are not readily equated with those of a recognized somasteroid genus; E, F, Somasteroidea indeterminate, UCBL-FSL 424964 (Reboul collection); Fezouata Formation, Early Ordovician (middle Floian), Zagora area, Central Anti-Atlas, Morocco. Aligned adaxial virgalia indicate a somasteroid; however, although representatives of other ossicular series can be identified, generic assignment is not justified; G, H, Chinianaster? sp., Saint-Chinian Formation, Early Ordovician (late Tremadocian); MBB-GG18 (Griffe collection); G, aboral view, virgalia are not readily equated with Chinianaster; enlarged, differentiated flange-like ossicles appear offset from axial series, as in Chinianaster (Fig. 2A); H, oral view; the small ossicles edging the upper margin suggest the ambital necklace of Chinianaster, as does the possible terminal (Fig. 2F); oral surface of axials retain an oral shield as Figure 2E. Abbreviations: fl, flange-like; mar, marginals; ter?, possible terminal; v, virgals; vir, virgalia. Scale bars: A-F, 3 mm; G, H, 5 mm. AB C D EF GH v mar v v fl ax ter? fl ax ax
482 COMPTES RENDUS PALEVOL • 2025 • 24 (23) Blake D. B. & Lefebvre B. PROBLEMATIC SPECIMENS Specimens too incomplete to fully assign at lower taxonomic levels are selected to illustrate the difficult nature of both the French/Moroccan suite (Fig. 14) and interpretation of early asterozoans in general. Crown-group asterozoans are difficult as well: Extensive sophisticated techniques enabled reevaluation of the large and well-known family Asteriidae (Fau etal. 2024), thereby obliquely addressing concerns surrounding evaluation of early asterozoans. SUMMARY AND INTERPRETATIONS The subphylum Asterozoa sensu Spencer (1951), Ubaghs (1953), and Spencer & Wright (1966) is accepted as monophyletic, “accepted” meaning in accord with current information while acknowledging potential paraphyly or polyphyly. Because morphologically diverse asterozoans are known from a comparatively narrow Early Ordovician stratigraphic interval and also because no tenable outgroup for phylogenetic analysis is recognized, divergence of the Asterozoa potentially preceded the emergence of a robust skeleton. Construction of the ambulacral column, consisting of the axials and adjacent adaxials, is fundamental to interpretation of the early phylogeny and taxonomy of Asterozoa whereas the extraxial skeleton, under more immediate environmental evolutionary pressures, is secondary. The Somasteroidea is interpreted as stemward among robustly skeletonized asterozoans. Specialization of the adradial-most virgals was emergent among somasteroids, with reduction to a single or few differentiated adaxials providing apomorphies that chart both the recognized classes as well as a number of genera not assigned at the class level. The complexity of somasteroid construction with only delicate linkages among ossicles is interpreted as reflecting body flexibility and mobile life modes with the oral surface directed toward the substrate. At least in part a reflection of this skeletal construction, the fossil record of the Somasteroidea is scanty. Yet ambiguities surround interpretation (and therefore any coding for phylogenetic analysis) of many aspects of axial and adaxial somasteroid development. Was the stemward positioning of axials at the arm midline offset or irregular (Figs 2A, E; 4A, B; 9-11; 13)? Presumably there was linkage between the radial water vascular channel and the podium, yet as survey of specimens shows, recognition is problematic. Are podial pores emergent within somasteroids (Figs 2A, F; 8G, H)? Are compound axials the product of axial fusion or are they a stemward aberrancy occurring before axial uniformity fully emerged (see Terminology; Figs 4C; 6C; 8D)? Should ossicles immediately lateral to axials be treated as “adaxials” or as representing a potentially independent series (see “Adaxial Skeleton”, Smith & Jell [1990])? Is there a separate “intervirgal strut” series (see “Adaxial Skeleton”, Dean Shackleton [2005])? What was the genesis of the so-called “radiole” (see discussions, figure citations under “The Ambital Framework”)? What is a “buccal slit” (see discussions under “Axial skeleton: Mouth frame”, many figures)? Do supernumerary ossicles occur in the mouth frame of some taxa (see discussions under “Axial skeleton: Mouth frame”, cited figures)? What is the nature and genesis of “marginal” series, and should ambital framework “marginals” be treated as adaxial or extraxial (see discussions under “The ambital framework”)? Somasteroid mouth frame ossicles are proportionately small and relatively little differentiated; however, understanding of asterozoan mouth frame construction is incomplete because of ossicular delicacy, overall body three-dimensionality, and animal flexibility in life, all leading to mouth frame disruption with death. In spite of the typical overall simplicity of the somasteroid mouth frame, possible supernumerary ossicles might occur (Thoralaster, Villebrunaster). Near-oral compound axials and complex first adaxial configurations occur (Thoralaster, Cantabrigiaster). Arm axials vary among genera, although ossicles of most are approximately bilateral and podial basins are proportionately large and equally shared by successive axials. Terminal ossicles known from derived lineages have not been recognized among somasteroids. Specialization of adradial-most virgals was emergent among somasteroids, with reduction to a single or few much differentiated ossicles providing the key apomorphies in the derivation and recognition of both class-level and unassigned lineages (e.g. Blake 2013, 2024). Abactinals vary among somasteroids but all are proportionately small and uniform within each genus. No phylogenetic sequencing of abactinal form within Somasteroidea is suggested. A madreporite has been recognized in only three somasteroid genera suggesting calcification of the presumed stemward hydropore might have been homoplastic within the class. An ambital framework series is recognized in all somasteroids arguing presence is plesiomorphic in the subphylum. Varied marginal expressions within the class suggest an evolutionary sequencing extending from many tiny platelets to a robust configuration similar to those of many Asteroidea. Absence of true marginals from the Ophiuroidea suggests loss was a classlevel apomorphy whereas status of differentiated arm margin ossicles in some Stenuroidea is problematic (Blake 2024). Because of constraints of preservation, accessories are generally difficult to recognize but appear to have been limited to proportionately small sizes and simple shapes. Somasteroids have been reported only from normal marine settings. Overall configuration and sedimentary occurrences argue mobile epifaunal habits with the mouth frame directed toward the substrate. Virgals are varied among somasteroids, expressions suggesting behavioral variation of an unknown nature. Disk configurations reflect substrate grazing or possible suspension-feeding with extension of the arms into the water column. That somasteroids exhibit essential asterozoan configuration has been recognized since the description of the first exemplar (Thoral 1935), yet the nature of the oral surface has allowed a multiplicity of interpretations important to the interpretation of asterozoan phylogeny and life mode: uncertainties persist.
483 Somasteroidea and early Asterozoa COMPTES RENDUS PALEVOL • 2025 • 24 (23) Acknowledgments Figure 1A is from “Early Palaeozoic Starfish”, W.K. Spencer, Philosophical Transactions of the Royal Society, Series B, reprinted by permission of The Royal Society (United Kingdom). Figures 1B, 12A, C, and E are from “Skeletal homologies, phylogeny and classification of the earliest asterozoan echinoderm”, J. Dean Shackleton Journal of Systematic Paleontology, copyright © 2005 The Trustees of the Natural History Museum, London, reprinted by permission of Taylor & Francis. Authors are grateful for the positive and helpful reviews of anonymous reviewers, and also for the editorial work provided by the associated editor, Annalisa Ferretti, and the editor-in-chief, Michel Laurin. This paper is a contribution to IGCP 735 “Rocks and the Rise of Ordovician Life” (Rocks n’ROL), and to the ANR project “Evolution of the Cambrian-Ordovician Biodiversification Onset Over Space and Time” (ECO-BOOST). Denis Audo and Jean-Michel Pacaud (MNHN, Paris), Emmanuel Robert (Université Lyon 1, Villeurbanne) and Roxelane Cicekli (Musée du Biterrois, Béziers) are thanked for having provided access to important specimens deposited in the collections they are curating. REFERENCES AgAssiz l. 1836. — Prodrome d’une monographie des radiaires ou échinodermes. Mémoires de la Société des Sciences naturelles de Neuchâtel 1: 168-199. AgAssiz A. 1877. — North American starfishes. Memoirs of the Museum of Comparative Zoology, Harvard College 5 (1): 1-136. https://www.biodiversitylibrary.org/page/4304838 AllAire n., lefebvre b., nArdin e., MArtin e. l. o., vAucher r. & escArguel g. 2017. —Morphological disparity analysis and systematic revision of the eocrinoid genus Rhopalocystis (Echinodermata, Blastozoa) from the Lower Ordovician of the central Anti-Atlas (Morocco). 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