Rugosphaeraster ruegensis, Gale, 2021

Gale, Andrew Scott, 2021, Taxonomy and phylogeny of the ‘ football stars’ (Asteroidea, Sphaerasteridae), Journal of Systematic Palaeontology 19 (10), pp. 691-741 : 739

Rugosphaeraster ruegensis sp. nov.

( Fig. 26A–Q )

Types. The group of associated ossicles, including abactinals and several poorly preserved ambulacrals, plus a single adambulacral ( Fig. 26A ), is the holotype ( SNSB-BGSP 2020 XLV4 ); the other figured ossicles are paratypes ( SNSB-BGSP 2020 XLV5-18 ). All are from the Lower Maastrictian of Rugen, Germany .

Derivation of name. After the Island of Rugen, Germany, where the species is common in Lower Maastrichtian chalks.

Material. There are over 200 isolated abactinal ossicles in the M. Kutscher Collection ( SNSB-BGSP) from the Lower Maastrichtian of Rugen, and three adambulacrals, collected by picking natural beach residues. A single abactinal is known from the Campanian of Ivo Klack, Skåne, southern Sweden ( NHMUK EE 17698).

Occurrence. Lower Maastrichtian of Rugen, Germany, and the Campanian of Ivo Klack, Skåne, southern Sweden.

Description. All abactinals are robust (height approximately half maximum breadth) and are of even thickness, with no taper to the margins. The lateral surfaces bear oval articulation surfaces (e.g. Fig. 26F, J ), which carry centrally positioned small holes that probably bore ligaments to attach adjacent plates. Broad papular notches, with rounded margins, are present between the articular surfaces. Some plates (e.g. Fig. 26A , central ossicle, G, L) bear a deep depression at one end, unique to this taxon. The external surfaces of the ossicles are flat, and bear coarse rugosities ( Fig. 26C, G ), or radially to transversely arranged ridges of imperforate stereom ( Fig. 26B, C, E, H, I, K ).

Abactinal plates ( Fig. 26B–L ) fall into a number of discrete categories. Plates originally from the central portion of the disc ( Fig. 26D, G ) are rounded in abactinal outline and have five to six short lobes of even size, and bear rounded rugosities arranged radially. Oval plates ( Fig. 26C, E ) were probably positioned on the sides of the body, with the pointed end directed actinally. Plates of irregular outline, bearing strips of raised stereom ( Fig. 26K–N ) were also likely to have been positioned laterally. Rhombic plates, in which the low ridges are parallel with the long axis, are analogous to the ‘I plates' developed in taxa such as Eosphaeraster amellagensis gen. et sp. nov. ( Fig. 17K, L ) and Podosphaeraster pulvillus ( Fig. 1C ) and would have been positioned on the central part of the actinal surface. Irregularly rhombic plates, with significant imbrication (slanting sides) and with deep grooves between the ridges ( Fig. 26H, K, N ), were also actinal in position and comparable with actinal plates of Sphaeraster tabulatus ( Fig. 9E ) and Echinosphaeraster scutatus ( Fig. 15A, B ). Tall ossicles with one straight margin ( Fig. 26M ) were probably positioned on the actinal surface, in articulation with the adambulacrals.

The adambulacrals ( Fig. 26O–Q ) are rectangular in abradial aspect, and taller than broad. The actinal surface is square, and carries a single row of small furrow spine bases, and large, irregularly arranged, bifid subambulacral spine bases ( Fig. 26O, P ). In proximal:distal aspect, a deep-set ligament pit is present ( Fig. 26P ) in place of adadm. In abactinal aspect ( Fig. 26Q ), padam is well developed, and dadam is replaced by a ligament pit. Ada1a, b are strongly inclined to the ambital surface, and ada2 and ada3 are horizontal.

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 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 15. Echinosphaeraster scutatus (Goldfuss, 1833). A, B, fragments of actinal surface; A, original of Quenstedt (1858, pl. 94, fig. 12) and Schondorf (1906a, pl. 1, figs 7, 8) (GPIT/80/94-12); B, original of Quenstedt (1858, pl. 94, figs 13, 14) and Schondorf (1906a, pl. 1, figs 9, 10) (GPIT/80/94-12). C, D, primary radial plate, in lateral (D) and external (C) views (GPIT/A5/52). E, K, large spine from abactinal plates, in basal (E) and lateral (K) views (GPIT/A5/51). F, G, I, J, abactinal plates (GPIT/A5/52). H, radial plate, external view (GPIT/A5/52). All specimens from the Weisser Jura e or Malm of the Swabian Alb, southern Germany. Scale bars: A–D, F, I, J = 10mm; E, K = 2 mm; G = 5 mm.

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 26. Rugosphaeraster ruegensis gen. et sp. nov. A, associated ossicles on surface of a flint nodule, holotype (SNSB-BGSP 2020 XLV4). B–N, isolated paratype abactinal/actinal ossicles, in lateral view (F, J, L) and external view (all others) (B–M, SNSB- BGSP 2020 XLV5-15; N, NHMUK EE 17698). O–Q, adambulacral ossicles in lateral (O), distal (P) and abactinal (Q) views (SNSB-BGSP 2020 XLV16-18). A–M, O–Q are from the lower Maastrichtian Chalk of Rugen, Germany. N is from the Campanian of Ivo Klack, Skåne, southern Sweden. Abbreviations: ada1, single distal amb-adamb articulation; ada2, proximal adradial ambadamb articulation; ada3, proximal abradial adamb-amb or adamb-adamb articulation; adadm, interadambulacral muscle; padam, proximal adamb-amb muscle. Scale bars: A = 10 mm; B–H, J–L = 0.5mm; I = 0.2 mm.