Eosphaeraster amellagensis, Gale, 2021

Gale, Andrew Scott, 2021, Taxonomy and phylogeny of the ‘ football stars’ (Asteroidea, Sphaerasteridae), Journal of Systematic Palaeontology 19 (10), pp. 691-741 : 714-718

Eosphaeraster amellagensis sp. nov.

( Figs 6F, G , 7I–K, M , 8F, I , 17A–M , 18A–F, 19A, C)

Types. The primary interradial ossicle figured here ( Fig. 17B ) is the holotype ( NHMUK EE 17657 ), the other figured ossicles are paratypes ( NHMUK EE17654, 17655, 17658–17669).

Diagnosis. As for the genus.

Derivation of name. After the village of Amellago, Morocco, where the type material was found .

Material. 200+ dissociated abactinal ossicles, predominantly abactinals, plus 30 adambulacrals, 10 ambulacrals and two orals ( NHMUK EE 17702 ). The material is believed to belong to a single species because ossicles have an identical surface sculpture of fine, evenly spaced granule pits and there are transitional forms between different abactinal ossicle types .

Occurrence. Early Jurassic (upper Pliensbachian) of an outcrop on the south side of the wadi immediately to the west of the road, 0.5 km south of the Kasbah of Amellago, Atlas Mountains, Morocco (Supplemental material, Fig. S1A ).

Description. Abactinal ossicles fall into two categories, and can be positioned by reference to more complete material of Sphaeraster tabulatus . Large abactinal ossicles from high on the disc are flat to slightly convex, either hexagonal or heptagonal in outline, and each has a central dimple (‘dorsal abactinals’). They carry an evenly spaced cover of spine pits set in a poorly defined rosette pattern and include plates identified as pir because they are characteristically heptagonal and contacted two interradial ossicles distally ( Fig. 16A, D ); symmetrical, hexagonal pr ( Fig. 17B, M ) and irregularly hexagonal abactinals.

The sides of the larger abactinals each carry a single, large, trapezoidal to oval articulation surface, on which are set five to 10 small rounded pits ( Fig. 17F, H ). A symmetrically arranged group of papular pores (two to five) is present on each corner of these plates, which originate by bifurcation from a single internal groove ( Figs 18B, C , 19A ), resembling a candelabra. The pr ( Fig. 17A, D ) are vertically symmetrical, hexagonal, with a broad proximal articulation surface and a narrower distal one for articulation with the adjacent radial. The pir ( Fig. 17B, M ) are heptagonal. Distinctively elongated, dimpled interradial abactinals are present; the precise position of these is uncertain ( Fig. 17C ). The interior surfaces of the primary abactinal ossicles are smooth with a concavity at each corner in which is set a ridge separating the papular notches ( Fig. 17I ). These concavities are deepest on the inner calycinal ossicles.

Smaller, hexagonal abactinals ( Fig. 17J–L ) with very different articulation structures (more actinally positioned abactinals) formed the sides of the domed body and are comparable with those in S. tabulatus . These vary from equidimensional to elongated hexagons in internal/external aspect, and the external surface carries spine pits in well-marked rows sub-parallel with the sides of the ossicle. The lateral articulation surfaces are highly modified, with three to six papular pores along each side, separated by vertical bars that articulate between ossicles ( Fig. 17G, K ). Each bar contains a single rounded concavity situated slightly exteriorly to the midpoint of the ossicle wall. The corners of the plates are formed of a curved buttress-like structure with a symmetrically placed shallow vertical groove. The more elongated hexagonal plates (I-plates) possess an internal swelling at one end that may protrude slightly ( Fig. 17K, L ), which could be a vertical interradial support structure. Ossicles intermediate in morphology between the larger ‘dorsal’ abactinal ossicles and the smaller ‘ventral’ ones are present. In these, one side carries only two articular bars, and the four to six articular structures.

The adambulacrals are highly variable in form along the length of the groove ( Fig. 7I–K, M ). All adambulcrals have similar faces contacting the ambulacrals. These are rectangular and the ambulacral articulation surfaces are positioned on the corners. The ada1a and ada1b are rounded and set on the distal margin of the ossicle, ada2 and ada3 on the proximal margin. Scars for insertion of padam and dadam are positioned centrally.

Type 3 adambulacrals, which are broader than tall, with discrete actinal and lateral surfaces, are set at about 120 Ǫ to each other. The adadm scar is oval and placed close to the actinal/abradial margin. These ossicles are remarkably similar in shape to those of Podosphaeraster . The adambulacrals of type 3 are smallest, and therefore perhaps were positioned closest to the terminal. In this case, the unusual tall ossicles of type 1 would have been most proximal in position.

The ambulacrals are very short and have an irregular, rectangular to triangular shape in proximal and distal view ( Fig. 6F, G ). Proximal and distal surfaces are broadly flat, with a gentle depression for passage of the tube feet. The head, shaft and base are poorly differentiated, and the heads imbricate slightly proximally. The dentition comprises two to three coarse ridges and grooves set obliquely to the long axis of the ossicles. Abtam and actam insertion sites are small and inconspicuous. A well-developed depression for lim is seen on the adradial, abactinal portion of the ossicles. The articulation surfaces for the adambulacrals are set on the actinal, abradial margins of the ambulacrals, on either side of an arched margin. The abradial articulation structures (ada1b, ada3) are set on one side of this arch, the adradial ones (ada2, ada1a) on the other. The ambulacrals taper very rapidly to the abradial margin, and the part of the ambulacral base involved in adambulacral articulation is consequently very short. The ambulacrals have a very prominent crest on the abradial, abactinal margin, similar to that in Valettaster (see below).

The body of the oral ossicle is triangular in outline ( Fig. 8F, I ), and the convex actinal and distal margins are set at right angles to each other. The articulation and muscle insertion for the first adambulacral (orada, oradam) are tall and parallel to the distal margin of the ossicle. The pb is short and carries a flat surface for articulation with the radial face of the adjacent oral ossicle. The external actinal face is small and triangular. The apophyse is rounded and directed proximally. The site for insertion of the riom (radial interoral muscle) on the proximal apophyse is small, and the pcoa and dcoa articulations are large and conspicuous. The interradial face of the oral has a slight concavity for articulation of the odontophore, and the insertion site of aciim (actinal interradial interoral muscle) is a narrow strip along the actinal/proximal border of the ossicle. The oral ossicle is similar to that of E. scutatus and of stauranderasterids, in the presence of a short pb and large, vertically oriented odadm.

Reconstruction of body form. The abactinal ossicles include plate morphologies similar to those of S. tabulatus , and indicate that the arrangement of large primary and inner calycinal ossicles was essentially similar ( Fig. 19C ). However, the highly specialized, candelabra-like papular notches ( Fig. 19A ), concentrated on the plate corners, and articular structures are very different to those present in S. tabulatus . The ‘ventral’ type of abactinal ossicles are similar to those of S. tabulatus , including numerous gently convex hexagonal ossicles, with margins notched by numerous papular pores. It is therefore reasonable to conclude that the central abactinal region was domed as in S. tabulatus , and that the larger, flat ossicles formed the upper part of the disc. The sides of the dome were constructed of smaller, hexagonal abactinals, bordered by numerous papular pores, as in S. tabulatus .

Affinities. As described above, the abactinal portion of the disc is similar to that of S. tabulatus in the size, number and arrangement of the ossicles, but differs in the nature of the papular notches and the presence of elongated interradial ossicles. The ambulacrals are short and comparable to those of Valettaster , and the adambulacrals resemble those of both Podosphaeraster and Valettaster .

Figures

Figure 1. Homology of abactinal plating in Podosphaeraster pulvinatus Rowe & Nichols, 1980. A–C, homology adopted in the present paper, which identifies the primary ossicles (interradials, radials), inner calycinal ossicles and radials. Marginals cannot be identified, and unpaired interradial plates (I-plate, V-plate) are indicated. D, E, plating scheme of Fujita & Rowe (2002, fig. 1), who identified an ‘apical system’ and marginals. See text for discussion.

Figure 6. Ambulacrals of sphaerasterids. A–D, Sphaeraster tabulatus (Goldfuss, 1833); A, B, proximal ambulacral in actinal and proximal/distal aspects, respectively (NHMUK EE 17633); C, D, actinal views of ambulacrals from mid-radius (NHMUK EE 17623a, 17634). E, P, Q, Podosphaeraster pulvinatus Rowe & Nichols, 1980; E, enlargement of actinal view of base of ambulacral; P, Q, actinal and proximal/distal views of ambulacral, respectively (Mnhnl OPH176). F, G, Eosphaeraster amellagensis gen. et sp. nov., ambulacral in actinal and proximal/distal views, respectively (NHMUK EE 17635). H–K, N, O, Valettaster argus (Spencer, 1907). H–K, proximal/distal views of ambulacral, note cavity replacing articulation facet (I); L, M, Bulbosphaeraster valettei gen. et sp. nov., ambulacral in actinal and proximal/distal views, respectively (NHMUK EE 17636); N, O, actinal views of ambulacrals (NHMUK EE 17637a, b). Provenance: A–D are from the upper Oxfordian, Hypsilum ammonite Zone, Plettenberg, near Balingen, Germany. F, G are from the upper Pliensbachian, outcrop on south side of wadi immediately to west of road, 0.5km south of the Kasbah of Amellago, Atlas Mountains, Morocco. L, M are from the lower Bathonian, Zigzagiceras zigzag ammonite Zone at La Pouza, near La Voulte-sur-Rhone, Ard̀eche, France. H–K, N–O are from the coranguinum Zone, Santonian, Broadstairs, Kent, UK. E, P, Q are Recent, Philippines. Scale bars: A, B, D, F, G, J–Q = 0.5mm; C = 1 mm; E, H, I = 0.2 mm.

Figure 7. Adambulacrals of sphaerasterids. A, B, Stauraster primaevus (von Zittel, 1880), adambulacrals in abactinal and proximal/ distal views, respectively (NHMUK EE 17638, 17632). C–H, L, N, Q, Sphaeraster tabulatus (Goldfuss, 1831); C, G, L, N, abactinal views (NHMUK EE 17623h–k); D, F, proximal/distal views (NHMUK EE 17623l, m); H, internal, Q, external views (NHMUK EE 17623n). I–K, M, Eosphaeraster amellagensis gen. et sp. nov.; I, J, proximal/distal and internal views (NHMUK EE 17639); K, M, proximal/distal views (NHMNUK EE 17640, 17641). O, S, T, Podosphaeraster pulvinatus Rowe & Nichols, 1980, adambulacrals in proximal/distal, internal and actinal views, respectively (MhnhL OPH174–176). P, R, Valettaster argus (Spencer, 1907), adambulacrals in abactinal and actinal views, respectively (NHMUK EE 17637f, g). Provenance: A, B are from the lower Oxfordian, Cardioceras bukowskii ammonite Subzone, basal Couches de Passage, Andelot Morval, Jura, France. C–H, L, N, Q are from the upper Oxfordian, hypsilum ammonite Zone, Plettenberg, near Balingen, Germany. I–K, M are from the upper Pliensbachian, outcrop on south side of wadi immediately to west of road, 0.5km south of the Kasbah of Amellago, Atlas Mountains, Morocco. P, R are from the coranguinum Zone, Santonian, Broadstairs, Kent, UK. O, S, T are Recent, Philippines. Scale bars: A, C–E, L–O, Q–T = 0.5 mm; B, F–K = 1 mm; P = 0.2 mm.

Figure 8. Oral ossicles of sphaerasterids. A–E, Sphaeraster tabulatus (Goldfuss, 1833); A, D, interradial view of orals of smaller individuals (NHMUK EE 17642, 17643); B, E, interradial (B) and radial (E) views of small oral (NHMUK EE 17644); C, large oral, interradial view (NHMUK EE 17623b). F, I, Eosphaeraster amellagensis gen. et sp. nov., oral in interradial and radial views, respectively (NHMUK EE 17645). G, oral ossicle of possible stauranderasterid or sphaerasterid, interradial view (MnhnL OPH173). H, oral ossicle, probably from Bulbosphaeraster valettei gen. et sp. nov., interradial view (NHMUK EE 17646). J, L, oral ossicle of Podosphaeraster pulvinatus Rowe & Nichols, 1980, in interradial and radial views, respectively (MhnhL OPH174–176). K, M, oral ossicle of Valettaster argus (Spencer, 1907), in interradial and radial views, respectively (NHMUK EE 17637h). N, interradial view of oral ossicle of Manfredaster bulbiferus (Forbes, 1848) (NHMUK EE 17647a). Provenance: A–E are from the upper Oxfordian, Hypsilum ammonite Zone, Plettenberg, near Balingen, Germany. F, I are from the upper Pliensbachian, outcrop on south side of wadi immediately to west of road, 0.5 km south of the Kasbah of Amellago, Atlas Mountains, Morocco. G is from the Carnian (Upper Triassic), Cortina d’Ampezzo, Italy. H is from the lower Bathonian, Zigzagiceras zigzag ammonite Zone at La Pouza, near La Voulte-sur-Rhone, Ard̀eche, France. K, M, N are from the coranguinum Zone, Santonian, Broadstairs, Kent, UK. J, L are Recent, Philippines. Scale bars: A, D, G, H, K, M = 0.5mm; B, E = 0.2 mm; C, F, I, J, L, N = 1 mm.

Figure 9. Sphaeraster tabulatus (Goldfuss, 1833). A, B, reconstructed fragments of the abactinal surface of an individual (NHMUK EE 17623h, i); A, shows the space occupied by the madreporite; B, largely consists of a row of radial plates. E, actinal fragment of same specimen (NHMUK EE 17623j). C, D, G, isolated distal abactinal or actinal plates (NHMUK EE 17623k–m). F, abactinal showing growth banding (NHMUK EE 17648). H, K, radial plate showing in vivo breakage (NHMUK EE 17649). I, J, spine originally attached to abactinal plate (NHMUK EE 17623n). L, O, small radial plates (NHMUK EE 17652, 17653). M, P, radial plate (NHMUK EE 17650). N, Q, very large primary radial plate, showing ring of spine attachment sites (NHMUK EE 17651). Provenance: upper Oxfordian, Hypsilum ammonite Zone, Plettenberg, near Balingen, Germany. Scale bars: A, B, F, M, N, P, Q = 10mm; C–E, G, H, L, O = 5 mm; I, J = 1 mm; K = 0.2 mm.

Figure 16. Echinosphaeraster scutatus (Goldfuss, 1833). Reconstructions and interpretative drawings. A, abactinal view of individual, colouration as in Figure 1. B, primary radial plate, to show papular openings. C, cross section of individual. D, drawing of specimen figured in Figure 13.

Figure 17. Eosphaeraster amellagensis gen. et sp. nov., abactinal ossicles. A, D, primary radials, paratypes (NHMUK EE 17654, 17656). B, primary interradial; holotype (NHMUK EE 17657), C, interradial, paratype (NHMUK EE 17660). E, abactinal plate of uncertain position (NHMUK EE 17663). I, centrale, paratype (NHMUK EE 17659). F–H, plates in lateral aspect, paratypes (NHMUK EE 17665, 17666, 17667). J, abactinal plate of uncertain position, paratype (NHMUK EE 17664). K, L, median interradial plates (I-plates) from actinal surface, paratypes (NHMUK EE 17661, 17662). M, primary interradial, paratype (NHMUK EE 17658). The internal process is arrowed. Provenance: all ossicles are from the upper Pliensbachian at an outcrop on south side of wadi immediately to west of road, 0.5 km south of the Kasbah of Amellago, Atlas Mountains, Morocco. Scale bars = 10mm.

Figure 18. A–F, Eosphaeraster amellagensis gen. et sp. nov., large abactinal ossicles; A, B, D, ossicle in external and lateral view and enlargement of surface, respectively, paratype (NHMUK EE 17668); C, E, F, abactinal ossicle with strongly marked growth increments, in external (F), internal (E) and lateral (C) views, paratype (NHMUK EE 17669). Provenance: all from the upper Pliensbachian at outcrop on south side of wadi immediately to west of road, 0.5km south of the Kasbah of Amellago, Atlas Mountains, Morocco. Scale bars = 10 mm.

Figure 19. A, C, interpretative drawings of Eosphaeraster amellagensis gen. et sp. nov. A, lateral view of large abactinal plate to show candelabra-like, outward-branching papular pores on rim of plate; C, reconstruction of part of abactinal surface; the large central ossicle is the primary interradial. Note concentration of papular pores towards corners of plates. B, Bolbosphaeraster valettei gen. et sp. nov. Note concentration of few papular pores at corners of plates. D, Pouzaster pocknotata gen. et sp. nov., to show single papular pores at plate junctions.