Rugosphaeraster, Gale, 2021

Gale, Andrew Scott, 2021, Taxonomy and phylogeny of the ‘ football stars’ (Asteroidea, Sphaerasteridae), Journal of Systematic Palaeontology 19 (10), pp. 691-741 : 736-739

Genus Rugosphaeraster gen. nov.

Type species. Rugosphaeraster ruegenensis sp. nov.

Diagnosis. Robust abactinal ossicles block-like, irregularly polygonal to rhombic, mostly equidimensional, with notches for papulae at the corners. Surface of the abactinal ossicles bearing transverse strips or irregularly radial pustules of imperforate stereom. Adambulacrals bear large, irregularly arranged, bifid spine bases.

Derivation of name. From the Latin ruga, with reference to the rugose and striated surfaces of the abactinals.

Remarks. Other than abactinals, only adambulacrals are known. The affinities of the genus are obscure, but the structure of the large abactinals and adambulacrals indicates that this genus belongs to the Sphaerasteridae . The robust structure of the abactinal plates, with vertical sides and large papular notches, is quite different to that found in Valettaster , in which the plates have the form of truncated cones, the spaces between which are packed with secondary ossicles to form a flat exterior surface ( Figs 23H–J , 24F, G ). In the very thick form, with large papular notches, the abactinal plates bear a resemblance to those of Stauraster primitivus ( Fig. 5D, F, L ), but this is probably convergent, and no broad radial plates like those of S. primitivus are present in the material. The morphology of some abactinal plate types of R. rugensis gen. et sp. nov. is closely comparable with those of other sphaerasterids. The rhombic to six-sided large, elongated abactinals are similar to actinal interradial ‘I plates’ (see below), and the small plates with slanting sides, indicating imbrication, are similar to actinally positioned ossicles of other sphaerasterids. The adambulacrals are typical of sphaerasterids, in the presence of tall abradial surfaces, a square actinal surface, proximal and distal:proximal pits for ligamentary attachment, and replacement of muscles by carious ligament pits; however, these characters are plesiomorphic for sphaerasterids and do not suggest generic affinities.

A well-preserved specimen of Rugisphaeraster ruegensis gen. et sp. nov. from the Campanian of Germany is present in the collections of the Berlin Museum, which shows the form of the abactinal surface, but is currently unavailable for study.

Figures

Figure 5. Morphology of the stauranderasterid outgroup, Stauraster primitivus (von Zittel, 1880). A–C, arm, in abactinal, lateral and actinal views, respectively (MZA L246). D–N, isolated ossicles; D–G, I, ossicles from primary circlet; D, E, primary interradial (NHMUK EE 17624); F, G, centrale (NHMUK EE 17625); H, ambulacral ossicle, actinal view (NHMUK EE 17626); I, inner calycinal ossicle (NHMUK EE 17627); J–L, radials (NHMUK EE 17628–17630); M, N, adambulacral ossicles, in abactinal and proximal/distal views, respectively (NHMUK EE 17631–17632). O, reconstruction of apical region of Stauraster. Provenance: A–C, upper Oxfordian of Switzerland. D–N are from the lower Oxfordian, Cardioceras bukowskii ammonite Subzone, basal Couches de Passage, Andelot-Morval, Jura, France (see Gale 2019, for locality details). Colours as in Figure 1. Scale bars: A–C = 10mm; D–G, I–L = 5 mm; H, M, N = 0.5 mm.

Figure 23. A, Valettaster ocellatus (Forbes, 1848), oblique actinal view of well-preserved individual (NHMUK E 5012). B–P, associated ossicles and fragments of Valettaster argus (Spencer, 1907); B–E, articulated adambulacrals, bearing subadambulacral spines (NHMUK EE 17637i–l); F, G, ambulacral ossicle, in proximal and distal views, to show bulbous swelling from ambulacral base ((NHMUK EE 17637m); H, external surface with ossicles in place (NHMUK EE 17637n). Note smaller secondary ossicles infilling gaps between external surfaces of larger abactinals, creating a smooth surface; I, J, fragments with articulated abactinal ossicles (NHMUK EE 17637o, p), showing smaller secondary plates and possible papular notches; K, fragment with madreporite and two abactinal ossicles (NHMUK EE 17637q); L, adambulacral in proximal/distal view, to show lack of adadm site and internally directed ledge (NHMUK EE 17637r); M–P, adambulacral ossicles; M, abactinal view of ossicle in which three of the articular surfaces each bear a cavity (NHMUK EE 17637f); N, proximal/distal view to show adadm site (oval depression) (NHMUK EE 17637s); O, oblique actinal view (NHMUK EE 17637t); P, actinal view, to show rugose perforate stereom and furrow spine attachment sites (NKMUK EE 17637g). Provenance: A, Santonian, Marsupites Zone, Brighton, Sussex, UK. B–P, Santonian, coranguinum Zone, level of Whitaker’s Flint, Broadstairs, Kent, UK. Distal adambulacrals marked with arrow. Scale bars: A = 10 mm; C = 1 mm; B, D–P = 0.5 mm.

Figure 24. A–G, Valettaster ocellatus (Forbes, 1848); A, B, interpretative drawings of NHMUK E 5012; C, D, interpretative drawings of abactinal surface of individual NHMUK E 5019. E, reconstruction of actinal surface, based on A. F, reconstructed detail of abactinal surface, to show smaller ossicles. G, reconstruction of abactinal surface, to show ossicle types. Provenance; A, B, from the Santonian, Marsupites Zone, Brighton, Sussex, UK; C, D, from the Coniacian or Santonian, coranguinum Zone, Micheldever, Hampshire, UK. Colours as in Figure 1. Note close similarity of ossicle arrangement to that of Podosphaeraster pulvinatus (Fig. 1). The interradial I-plate is arrowed. Scale bar = 10 mm.