FIGURE 7-1 - uploaded by Daniel B Blake
Content may be subject to copyright.
, 2, the ophiuroid Protaster sedgwickii Forbes, paratype SM A6374b, ventral views; ambulacrals are hammer-shaped and offset, the laterals robust, extended distally and closing the podial basins; 3-5, the stenuroid Pradesura jacobi (Thoral), FSL 168 688: 3, ventral view, ambulacrals cup-shaped, irregularly alternate, rimmed by an embedded virgal (arrow); 4, inclined dorsal view of mouth frame area; little-differentiated ambulacral series converging distally; proximal ambulacrals (upper arrows) not differentiated as in ophiuroids; a depressed longitudinal groove of ambulacrals (lower right arrow) is similar to expression in Chinianaster (Fig. 1.1); 5, collapsed disk margins do not represent a differentiated ambital frame; madreporite (arrow); 6, the stenuroid Eophiura bohemica Schuchert, MCZ 140218; both embedded virgals and outer virgals are plate-like and unlike those of other stenuroids and ophiuroids; ambulacrals square, cup-shaped similar to those of Pradesura (Fig. 7.3), abradial edge Y-shaped indicating flexibility; 7, the ophiuroid Stenaster salteri Billings, UI-X-8888, Bobcaygeon Fm., and 8, the asteroid Phyrtosaster casteri Blake, CMC TT5305, Fairview Fm.?, the similar mouth frame construction
Source publication
The Asterozoa as traditionally recognized is monophyletic, although ancestry within the Echinodermata is unknown. The asterozoan class Somasteroidea is most readily recognized by presence of series of simple ossicles termed virgals that extend laterally from each ambulacral ossicle. Virgal series reduction to two or three together with ossicular sp...
Contexts in source publication
Context 1
... facilitate comparisons, figures cluster the class groupings recognized here: somasteroids ( Fig. 1), those stenuroids that are unlike either asteroids or ophiuroids (Figs. 2-4), largely asteroids and asteroid-like stenuroids (Figs. 5, 6), and a mixed grouping (Fig. 7 A computer-based hypothesis of Ordovician asterozoan phylogeny was provided by Shackleton (2005), and selected genera from the span of asteroid history were treated in Blake et al. (2000) and Blake and Hagdorn (2003). Although published before computer-based techniques were available, important interpretations of early asterozoan ...
Context 2
... The ambital frame found in a few ophiuroids was judged not to be homologous with those of somasteroids because in ophiuroids ossicles arise along the arm (Shackleton, 2005). Disk collapse during ophiuran preservation can superimpose disk edge ossicles in a potentially misleading manner reminiscent of an ambital framework (Spencer, 1925, p. 277; Fig. 7.5 in a stenuroid). Because of these difficulties, the term ''ambital frame'' is used descriptively without implication of ...
Context 3
... that clear skeletal linkages between asterozoans and a more basal echinoderm group might never be found. A posited increase in calcification of the body wall through time (e.g., Spencer, 1914, p. 8;Schuchert, 1915, p. 31) would be consistent with an asterozoan record beginning with trace fossils, although weakly calcified extant species (e.g., Fig. 6.7) allow the possibility of secondary ...
Context 4
... treatment of mouth frame construction, Spencer (1925, p. 268, 270) interpreted the dorsal aspect of the Ordovician ophiuroid Lapworthura Gregory, 1897, as asteroid-like whereas the ventral configuration was found to be distinctive. The ventral proximal ambulacra and mouth frame arrangement of the Ordovician asteroid Phyrtosaster Blake, 2007 ( Fig. 7.8) is similar to that of the ophiuroid Stenaster Billings, 1858, (Fig. 7.7), and the Y-shaped internal configuration of the mouth frame of Jugiaster, Blake, 2007 (Fig. 5.5) is similar to those of many early ophiurans ( Fig. 7.2), with enlarged mouth frame regions associated with buccal podia. In external aspect, the appearance of the ...
Context 5
... the dorsal aspect of the Ordovician ophiuroid Lapworthura Gregory, 1897, as asteroid-like whereas the ventral configuration was found to be distinctive. The ventral proximal ambulacra and mouth frame arrangement of the Ordovician asteroid Phyrtosaster Blake, 2007 ( Fig. 7.8) is similar to that of the ophiuroid Stenaster Billings, 1858, (Fig. 7.7), and the Y-shaped internal configuration of the mouth frame of Jugiaster, Blake, 2007 (Fig. 5.5) is similar to those of many early ophiurans ( Fig. 7.2), with enlarged mouth frame regions associated with buccal podia. In external aspect, the appearance of the mouth frame of this genus is closely arranged and bud-like in appearance, as ...
Context 6
... specimens of Furcaster Stuertz, 1886, Lapworthura, Pectenura Haude, 1982, Stenaster, Taeniaster Billings, 1858, these constructions implying that differentiation of well-defined disks described by MacBride (1906) had not yet emerged. Potentially misleading are portions of disk-like collapsed dorsal surfaces extended into interbrachia (e.g., Fig. 7.5); different expressions among interbrachia and specimens of a single species provide guides to ...
Context 7
... asteroids, the radial water canal is external but partially enclosed and protected by the vaulting of the ambulacral furrow; consistent with a protective interpretation are the skeletal platelets that lie below the radial water canal and at the peak of the furrow of the lightly skeletonized living asteroid Asteropsis Müller and Troschel, 1840 ( Fig. ...
Context 8
... the most appealing candidate for title of ''proto- ophiuroid'' among stenuroids is Pradesura Spencer, 1951 ( Fig. 7.3-7.5), which has a well-defined disk built of uniform, overlapping scales, a ventral madreporite, cylindrical arms, and a mouth frame that is broadly Y-shaped and ophiuroid-like. Disk and arm expressions have not been consistently treated as basal apomorphies of the Ophiuroidea. The disks of many early ophiurans, including Stenaster ...
Context 9
... arc arising at the point of linkage of the virgal series to the abradial margin of the ambulacral, which commonly is recurved or broadly Y-shaped (e.g., Fig. 1.6, arrow; 1.7), thereby providing a rotational socket; a folding hand fan is analogous. Mobility of the outer virgal was stressed by Spencer (1951) for Rhopalcoma ( Fig. 5.2) and Eophiura (Fig. 7.6), and imbricating outer virgals with complex muscular facets (Fig. 4.4, 4.5) as well as differing orientations of outer virgal series within species of stenuroids (Figs. 2, 3) also indicate retention of mobility within this ...
Similar publications
The class Somasteroidea Spencer, 1951, is basal within the subphylum Asterozoa. Members are most readily recognized by presence of series of rod-like so-called virgal ossicles extending laterally from each ambulacral ossicle. Five somasteroid genera are recognized and assigned to two families. Four genera are Gondwanan, three of these (
Chinianaste...
Citations
... The high-latitude regions of the Mediterranean Province (France and Morocco) and nearby areas from Avalonia (United Kingdom) represent the second diversity hotspot for Early Ordovician asterozoans. In the Montagne Noire (southern France), the Saint-Chinian Formation (late Tremadocian) has yielded the most diverse assemblage of early asterozoans including somasteroids (Chinianaster levyi Thoral, 1935, Villebrunaster thorali Spencer, 1951, and Thoralaster spiculiformis Dean Shackleton, 2005, and stenuroids (Pradesura jacobi (Thoral, 1935)) (see Thoral 1935;Spencer 1951;Fell 1963;Vizcaïno & Lefebvre 1999;Dean Shackleton 2005;Blake 2013;Blake & Guensburg 2015). In this region, yet undescribed ophiuroids and stenuroids (cf. ...
... Ubaghs 1953;Spencer & Wright 1966;Dean Shackleton 2005; Blake 2018) is readily treated as monophyletic while also recognizing potential for paraphyly or polyphyly. Beginning with designation of the Somasteroidea as stemward among asterozoans (Spencer 1951;Blake 2013), the history of the class Asteroidea was marked by relatively few fundamental changes in skeletal configuration, "fundamental" descriptively defined as differences likely to receive emphases at higher taxonomic levels. ...
A large and taxonomically diverse collection of Ordovician Asterozoa from France and Morocco enables new insights into the early evolution of the subphylum. Available specimens of both Asteroidea and Stenuroidea are comparatively few, the collection dominated by Ophiuroidea and to a lesser extent, Somasteroidea. Nearly all the asteroid specimens are assigned to Petraster Billings, 1858; P. caidramiensis n. sp. is differentiated based on the complexity of the extraxial skeleton. The genus Petraster is reviewed. Another asteroid fragment, Euaxosida sp. A, is too incomplete to assign below the ordinal level. Among species of Petraster, the extraxial skeleton suggests homoplastic emergence of ossicular series definition whereas evolution of ambulacral axial-adaxial series expressions was conservative. The stemward asteroid axial/adaxial configuration is considered largely a plesiomorphic derivative of the somasteroid condition. Ossicular details of all series, however, differ among Petraster species. Euaxosida sp. A also offers oral-surface expressions suggestive of a transitional status. Differences among ossicular series expressions exemplify concerns surrounding interpretation of early asterozoan phylogeny and taxonomy.
... The Paleozoic is dominated by what is called 'archaic' type ophiuroids. These ophiuroids have an arm morphology very different from that of 'modern' type or crown group ophiuroids [1,2]. 'Archaic' and 'modern' ophiuroids diverged in the Early Ordovician and until recently, 'archaic' ophiuroids were thought to have become extinct by the latest Carboniferous [3]. ...
For the first time, ophiuroids have been found in South African strata predating the lowermost Bokkeveld Group. These comprise natural moulds and casts from two localities in the ‘upper unit’ of the Baviaanskloof Formation (Table Mountain Group). As a Pragian to earliest Emsian age has been inferred for this member, the new taxa comprise the earliest high-palaeolatitude ophiuroid records from southern Gondwana. Morphological analysis of the specimens revealed the presence of two distinct taxa. One is here described as Krommaster spinosus gen. et sp. nov., a new encrinasterid characterised by very large spines on the dorsal side of the disc, the ventral interradial marginal plates and the arm midlines. The second taxon is a poorly preserved specimen of Hexuraster weitzi , a cheiropterasterid previously described from the slightly younger Bokkeveld Group.
... 2) designated somasteroids as a 'family'. Further illustrating difficulties surrounding interpretation, the Somasteroidea has been treated as the 'first' asterozoans (e.g., Spencer, 1951: p. 87;Fell, 1962aFell, , 1962bFell, , 1963aFell, , 1963bBlake, 2013;Hunter and Ortega-Hernández, 2021), one of three branches of an asterozoan polytomy (Smith and Jell, 1990: fig. 52), polyphyletic within the Asterozoa (Mooi and David, 2000), and near to the base of the ophiuran branch of asterozoan diversification (Shackleton, 2005). ...
... In a series of publications, including David (2000, 2008), the authors began with the Spencer and Wright (1966) classification, but found the 'adaxial' subdivision to be conceptually problematic and not applicable in Echinodermata beyond the Asterozoa whereas Blake (2018) found the term useful, retaining the Spencer and Wright (1966) concept. Asterozoan skeletal classification has been treated in detail in a number of titles (Spencer, 1914(Spencer, -1940(Spencer, , 1951Hotchkiss, 1993Hotchkiss, , 2009Hotchkiss, , 2012Shackleton, 2005;Blake, 2013Blake, , 2018Blake and Guensburg, 2015). ...
... Herein, only the composition of the data matrix of Hunter and Ortega-Hernández (2021) is of concern; soundness of the analyses is not. Presentation and analysis of a new data matrix at the present level of understanding would obscure the hypothesis that the phylogenetic origin of the Asterozoa preceded the origin of a readily preserved skeletal construction, an argument founded in part on problematic Cambrian trace fossils (e.g., Alpert, 1976); also on the disparate Cambrian echinoderm fauna lacking exemplars clearly indicative of the Asterozoa; and finally, the comparatively abrupt appearance in Early Ordovician strata of morphologically diverse asterozoans (Blake, 2013(Blake, , 2018Blake and Guensburg, 2015). ...
A proposed new Ordovician asterozoan genus and species, Cantabrigiaster fezouataensis, has been recently described and assigned to the class Somasteroidea. An accompanying phylogenetic analysis treated twenty-two asterozoans and sixteen early non-asterozoans, one of the latter providing the outgroup. The phylogenetic hypothesis focused on derivation of the subphylum Asterozoa and emphasized the Crinoidea; Cantabrigiaster fezouataensis was interpreted as documenting a critical transition stage in the origin of the Asterozoa. The diagnosis for the proposed new generic name posits absence of ambital framework ossicles as the single character expression that distinguishes Cantabrigiaster among somasteroid genera. Ambital framework ossicular presence is documented here in the holotype and other members of type suite; Cantabrigiaster is synonymized with Villebrunaster Spencer and V. fezouataensis nov. comb. is redescribed. The data matrix for the former Cantabrigiaster phylogenetic analysis relies on an earlier study treating overall echinoderm construction. Expressions outlined in the earlier study are not amenable to transfer to a data matrix without evaluation of level of universality of each cited expression; such evaluations were not provided thereby leading to flawed phylogenetic conclusions that are rejected. An alternative hypothesis for the early history of the Asterozoa supported by aspects of the fossil record, that subphylum diversification preceded the origin of readily preserved skeletons, and therefore potentially no tenable pre-asterozoan outgroup candidate survives in the fossil record, has not been falsified.
... Asterozoans. Asterozoa is a diverse subphylum of free-living echinoderms represented by the extant classes Asteroidea (starfish) and Ophiuroidea (brittle stars), and the extinct basal class Somasteroidea, which shares characteristics with both extant groups (Blake 2013;Blake & Guensburg 2015). In contrast to the Lower Ordovician Fezouata Shale, where asterozoans are represented exclusively by somasteroids (Lefebvre et al. 2016b;Hunter & Ortega-Hernández 2021), the Tafilalt Biota is dominated by ophiuroids (Figs 8 & 9), with asteroids only making an appearance in the youngest deposits of the area; somasteroids are entirely absent from the Tafilalt. ...
The extensive, predominantly siliciclastic deposits of the Upper Ordovician of the Tafilalt have long been the subject of scientific investigation. In the past 25 years, intensified collecting for commercial purposes has resulted in the discovery of several exceptionally-preserved faunas ( Konservat-Lagerstätten ) in the Tafilalt region, preserving a range of non-biomineralised and soft-bodied organisms. The preservation of these fossils in the coarse clastic sediments of the Tafilalt is surprising, and in the case of soft-bodied organisms, remarkably similar to the preservational mode of typical Ediacaran biotas. These relatively recent discoveries have increased the scientific significance of the Tafilalt Biota, providing an unparalleled insight into the composition and temporal evolution of the shallow, open-marine ecosystems and their denizens during the later stages of the Great Ordovician Biodiversification Event. At least nine different phyla, in addition to several soft-bodied problematica are represented in the Tafilalt. While the highly diverse and remarkably well-preserved echinoderm and euarthropod faunas are most emblematic for the Tafilalt Biota, further studies have revealed a relatively high diversity of molluscs and brachiopods. Among soft-bodied fossils, the problematic paropsonemid eldonids are iconic for the Tafilalt and stand out both through their abundance, and their wide temporal and geographic range throughout the area.
... Asterozoans-whose most familiar members include starfish and brittle stars-are the dominant group of extant echinoderms based on their diversity, abundance and biogeographic distribution [1]. Despite their ecological success and a fossil record spanning more than 480 Myr [2][3][4], the origin and early evolution of asterozoans, and those of crown-group echinoderms more generally, remain uncertain given the difficulty of comparing the organization of the calcified endoskeleton in diverse Lower Palaeozoic groups, such as the edrioasteroids and blastozoans [5][6][7][8][9][10][11][12][13]. The extraxial-axial theory (EAT), which supports the homology of the biserial ambulacral ossicles of pentaradial and non-pentaradial echinoderms based on embryonic and ontogenetic data [14][15][16], has been proposed as a developmentally informed model that facilitates comparisons among groups with disparate morphologies. ...
... The presence of virgal ossicles in Cantabrigiaster strongly supports its affinities with somasteroids [2,[5][6][7][8][9]. Cantabrigiaster bears the greatest similarity to the Tremadocian taxa Chinianaster, Thoralaster and Villebrunaster (electronic supplementary material, figure S5), but is unique among somasteroids in lacking ossicles along the abaxial lateral margins of the arms ( figure 1a,d). ...
... The arm construction of Cantabrigiaster consists of flattened and offset biserial ambulacrals, each of which articulates with an abaxially oriented perpendicular series composed of simple virgal ossicles (electronic supplementary material, figure S4). In addition to these features, the arms of all other somasteroids also possess a series of axially oriented ossicles along the lateral margins that vary from small and bead-like-albeit with occasional spikes-in Tremadocian taxa [2,5,6] (electronic supplementary material, figure S5a,b), to robust and block-like in the stratigraphically younger (Floian) Ophioxenikos figure S4), whereas other somasteroids record the first appearance of these structures along the edges of the arms, and their subsequent changes in size and shape. Based on this sequence, we propose that the origin of new axially oriented ossicle series in early asterozoans required their formation on the abaxial edges of the arms. ...
The somasteroids are Lower Palaeozoic star-shaped animals widely regarded as ancestors of Asterozoa, the group of echinoderms that includes brittle stars and starfish. However, the origin of asterozoans, the assembly of their distinctive body organization, and their relationships with other Cambrian and Ordovician echinoderms remain problematic owing to the difficulties of comparing the endoskeleton between disparate groups. Here, we describe the new somasteroid Cantabrigiaster fezouataensis , a primitive asterozoan from the Early Ordovician Fezouata Lagerstätte in Morocco. Cantabrigiaster shares with other somasteroids a unique endoskeletal arm organization and the presence of rod-like virgal ossicles that articulate with the ambulacrals, but differs from all other known asterozoans in the absence of adambulacral ossicles defining the arm margins, evoking parallels with non-asterozoan echinoderms. Developmentally informed Bayesian and parsimony phylogenetic analyses, which reflect the homology of the biserial ambulacral ossicles in Palaeozoic echinoderms according to the extraxial–axial theory, recover Cantabrigiaster as the earliest divergent stem-group asterozoan. Our results illuminate the ancestral morphology of Asterozoa, and clarify the affinities of problematic Ordovician Asterozoa. Bayesian inference and parsimony demonstrate that somasteroids represent a paraphyletic grade within stem- and crown-group Asterozoa, whereas stenuroids are paraphyletic within stem-group Ophiuroidea. Our results also offer potential insights on the evolutionary relationships between asterozoans, crinoids and potential Cambrian stem-group representatives.
... However, the euryalids were found to be a monophyletic clade nested within the Ophiurida and the Ophiomyxidae were resolved elsewhere within the Ophiurida based on a molecular phylogenetic analysis [14]. Now, asterozoans are typically assigned to four major groups: Somasteroidea, Asteroidea (fossil and living sea stars), Ophiuroidea (fossil and living brittle stars) and Stenuroidea [15]. Oegophiuroida and Euryalida are included within Ophiuroidea [12]. ...
... Ophiuroids have been hypothesized to have evolved from a somasteroid ancestor [15,18]. The relationship between Stenuroidea and crown ophiuroids remains uncertain [17]. ...
Living brittle stars (Echinodermata: Ophiuroidea) employ a very different locomotion strategy to that of any other metazoan: five or more arms coordinate powerful strides for rapid movement across the ocean floor. This mode of locomotion is reliant on the unique morphology and arrangement of multifaceted skeletal elements and associated muscles and other soft tissues. The skeleton of many Palaeozoic ophiuroids differs markedly from that in living forms, making it difficult to infer their mode of locomotion and, therefore, to resolve the evolutionary history of locomotion in the group. Here, we present three-dimensional digital renderings of specimens of six ophiuroid taxa from the Lower Devonian Hunsrück Slate: four displaying the arm structure typical of Palaeozoic taxa ( Encrinaster roemeri, Euzonosoma tischbeinianum, Loriolaster mirabilis, Cheiropteraster giganteus ) and two ( Furcaster palaeozoicus , Ophiurina lymani ) with morphologies more similar to those in living forms. The use of three-dimensional digital visualization allows the structure of the arms of specimens of these taxa to be visualized in situ in the round, to our knowledge for the first time. The lack of joint interfaces necessary for musculoskeletally-driven locomotion supports the interpretation that taxa with offset ambulacrals would not be able to conduct this form of locomotion, and probably used podial walking. This approach promises new insights into the phylogeny, functional morphology and ecological role of Palaeozoic brittle stars.
... Second, a characteristic lateral arm plate of the genus Pectenura Haude, 1982 was found (Fig. 4d). Boczarowski (2001) still attributed the genus to the ophiuroid order Stenurida Spencer, 1951, but Blake (2013 supposed the stenurids to constitute a separate monophyletic Palaeozoic echinoderm class Stenuroidea. However, paraphyly of the class was not excluded by Blake (2013) and assumed by O'Hara et al. (2017). ...
... Boczarowski (2001) still attributed the genus to the ophiuroid order Stenurida Spencer, 1951, but Blake (2013 supposed the stenurids to constitute a separate monophyletic Palaeozoic echinoderm class Stenuroidea. However, paraphyly of the class was not excluded by Blake (2013) and assumed by O'Hara et al. (2017). Recently, Hunter & McNamara (2018) regarded both the Oegophiurida and the Stenuroidea as the "arcaic" stem group of ophiuroids. ...
... Taxonomy of ophiuroids relies on Frizzell & Exline (1956 and Boczarowski (2001); for the stenuroids on Haude (1982), Boczarowski (2001) and Blake (2013); for the holothurians on Frizzell & Exline (1956, Gilliland (1993) and Miller et al. (2017); for the ophiocistioids on Reich & Haude (2004), Reich & Kutscher (2014) and Reich et al. (2018). ...
For the first time an echinoderm microfauna is recorded from the cephalopod limestone facies (‘griotte facies’) of the lower Carboniferous (Mississippian) Genicera Fm. (Alba Fm.). The formation is widespread in the Cantabrian Mountains in NW Spain, but the ossicles are from some sections in the surroundings of the Bernesga valley in northern León. They have been derived from insoluble acetic acid residues from samples of the upper and especially of the uppermost part of the formation (Canalón Mb. and Millaró Beds). The microfauna include taxonomically treated wheel-shaped ossicles, sieve-plates and rods of holothurians, goniodonts of ophiocistioids, and ophiuroid and stenuroid skeletal elements. From the Palaeozoic of Spain, Ophiocistioidea, Stenuroidea, Apodida (Holothuroidea), and allagecrinids (microcrinoids) are first reported. Here, we describe two new species: Linguaserra heidii n. sp. (Ophiocistioidea) and Calclyra bifida n. sp. (Ophiuroidea). Indeterminate echinoderm remains are also figured and discussed. The findings stress the importance of a diverse but still poorly documented echinoderm fauna in Upper Mississippian psychrospheric pelagic environments.
... Although Asterozoa is recognized as a monophyletic group, higher taxonomic affinities within the Palaeozoic taxa still can be controversial (Blake, 2013). Therefore, family level classification is carefully attempted herein, pending additional investigation. ...
... However, as some affinities are shared with Asteroidea and Ophiuroidea, higher taxonomic assignments may be problematic for M. darwini. Blake (2013) elevated Stenurida to class level, the Stenuroidea, and included many asteroid-like and ophiuroid-like genera, as well as tentatively Echinasterella, and consequently 'E.? darwini'. Indeed, with large podial basins, marginals not recognized, and relatively spaced adambulacrals, M. darwini could be assigned to Stenuroidea. ...
... But this Brazilian species has not accessory plates, interbrachial scales, deep podial basins or mainly alternate ambulacrals. In addition, as virgal series (or embedded virgals, according to Blake, 2013) are not observed herein, there is great uncertainty whether M. darwini is a stenuroid. ...
... Because of their stratigraphic range and palaeobiogeographic distribution in the Ordovician, asterozoans are more likely candidates: their oldest known representatives have been documented in Lower Ordovician deposits (Thoral 1935;Blake 2013;Jell 2014;Blake & Guensburg 2015), and their presence is recorded in Baltica at least from the Dapingian, i.e., as early as the oldest known occurrence of Bolboporites (Pisera 1994;Hansen et al. 2005;Rozhnov 2005;Blake & Rozhnov 2007;Tinn & Ainsaar 2014). However, Bolboporites clearly does not show any character supporting its interpretation as an isolated asterozoan spine. ...
Bolboporites is an enigmatic Ordovician cone-shaped fossil, the precise nature and systematic affinities of which have been controversial over almost two centuries. For the first time, a wide range of techniques (CT-scan, SEM, cathodoluminescence, XPL, UV epifluorescence, EBSD, FT-IR and XRF spectrometry) were applied to well-preserved specimens of Bolboporites from Norway and Russia. Our main finding confirms its echinoderm affinities, as shown by its stereomic microstructure and by the first definitive evidence of its monocrystalline nature. Each cone consists in a single, microporous calcitic crystal with a narrow longitudinal internal canal. These results are combined with all previous data on Bolboporites to critically discuss five alternative interpretations of this fossil, namely theca, basal cone, spine, columnal, and holdfast, respectively. The most parsimonious scenario considers Bolboporites as an isolated spine, which was articulated in life by a short biserial appendage to the body wall of an unknown echinoderm, possibly of echinozoan affinities.
... Since Fell (1963) and Spencer and Wright (1966), additional and commonly divergent viewpoints on asterozoan classification and phylogeny have been offered by Kesling (1969), McKnight (1975), Shackleton (2005), Blake (2013Blake ( , 2014Blake ( , 2018, and Villier et al. (2017). , augmented in Blake and Guensburg (2015), included overview phylogenetic analyses of the Asterozoa, but these phylogenetic interpretations are not revisited in part because the ophiuran affinities of Cholaster are clear and in part because the approach here is directed toward specific morphologies and taxa. ...
Newly discovered, relatively well-preserved specimens of Cholaster whitei n. sp. (Ophiuroidea, Echinodermata) are described from a small area of extensive outcrop of the Bangor Limestone (Mississippian, Chesterian) exposed on the edge of Cedar Creek Reservoir in northern Alabama, USA. The only other known species of the genus, C . peculiaris Worthen and Miller, is based on a single specimen exposed in dorsal aspect and collected from strata of similar age from southwestern Illinois. Incomplete preservation of the single C . peculiaris specimen limits comparisons, but differences between the two occurrences support separation at the species level.
Skeletal remains of both asteroids and ophiuroids are first recognized from Early Ordovician sediments, and representatives of the two classes have retained plesiomorphies or converged morphologically since that time, thereby suggesting important evolutionary potentials and limitations. Cholaster is asteroid-like and unusual among ophiuroids in that the arms are comparatively broad and strap-like, and lateral ossicles are similar to asteroid adambulacrals and marginals, whereas the “vertebrae” (i.e., fused axial pair) and oral frame configurations of C. whitei n. sp. are typical of the Ophiuroidea. The oral frame of C. peculiaris is unknown.
A poorly preserved specimen of the asteroid Delicaster ? also was recovered from nearby strata associated with the C. whitei n. sp.
UUID: http://zoobank.org/e0eea445-58e5-4096-80c1-a65964832ef6
