Sphaeraster tabulatus
Creators: name: Gale, Andrew Scott
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Echinodermata
Asteroidea
Valvatida
Sphaerasteridae
Sphaeraster
Sphaeraster tabulatus

description: Sphaeraster tabulatus (Goldfuss, 1833)
(Figs 3A–K, 6A–D, 7C–H, L, N, Q, 8A–E, 9A–Q, 10A, B, 11, 12, 13A–H, P)
$1833 Asterias tabulatus Goldfuss: 210, pl. 63, fig. 7c–q.
1875 Sphaerites punctatus Quenstedt: 651, pl. 80, figs 23–27.
1875 Sphaerites punctatus juvensis Quenstedt: 650, pl. 80, figs 28–38.
1875 Sphaerites tabulatus (Goldfuss); Quenstedt: 651, pl. 80, figs 39–47.
1906b Sphaeraster punctatus (Quenstedt); Schondorf: 263, pl. 24, figs 1–4; pl. 25, figs 14–20, 29, 30.
1906b Sphaeraster juvensis (Quenstedt); Schondorf: 260, pl. 24, figs 5, 6.
1906b Sphaeraster annulosus (Quenstedt); Schondorf: 264, text-fig. 4.
1906b Sphaeraster tabulatus (Goldfuss); Schondorf: 263, text-figs 2, 3.
1975 Sphaeraster tabulatus (Goldfuss); Hess: 37, pl. 7, figs 7, 8.
1984 Sphaeraster punctatus (Goldfuss); Blake: 76, fig. 1A, D.
1984 Sphaeraster tabulatus (Quenstedt); Blake: 76, figs 1H, 2C, 3, 4B–D, 5, 8D.
2009 Sphaeraster punctatus (Quenstedt); Neumann: 92, figs 1–3.
Type. The abactinal ossicle figured by Goldfuss (1833, pl. 63, fig. 7c–e) is here selected as lectotype. The present whereabouts of this specimen are uncertain; possibly it is in the Berlin (MfB) or Munich (SNSB) collections. The synonymy proposed by Hess (1975), who placed S. punctatus, S. juvensis and S. annulosus as subjective junior synonyms of Goldfuss’ species, is followed here.
Diagnosis. As for the genus.
Material. Ossicles of the ambulacral groove (Figs 3A–K, 6A–D, 7) and mouth frame (Fig. 8A–E) were found in associated material from the Oxfordian of Plettenberg, which also yielded abactinal ossicles (Fig. 8). Large abactinal ossicles are found in the collections at Stuttgart and Tubingen and in private collections. Several specimens show the construction of the abactinal surface, with 10–20 ossicles in situ (Figs 10–12). The best of these individuals was figured by Quenstedt (1875, pl. 80), Schondorf (1906a, pl. 24, figs 1, 2) and Blake (1984, fig. 1D); this is an undistorted upper portion of the disc including pi and pir and inner calycinal plates with periproct and madreporite (GPIT /67882). A further specimen showing in-place abactinal plating from the Kimmeridgian (Malm Χ) of Geisingen (southern Germany) is in the private collection of G. Heinssen-Levens at Haseldorf (Neumann 2009). Two specimens from the upper Oxfordian (hypsilum ammonite Zone of Plettenberg, southern Germany) have been particularly important for the present paper. One of these (NHMUK EE 17655) shows articulated distal abactinal ossicles, down to R7, while the other comprises about 500 associated ossicles including abactinals, actinals, ambulacral, adambulacral, circumoral and oral ossicles (NHMUK EE 17623). Other ossicles from the same locality include juveniles (NHMUK EE 17648–17653; 17680–17687). The species is also known from Switzerland (Hess 1975) and France (lower Oxfordian at Andelot-Morvan, French Jura, two ossicles, pers. obs. Gale 2019).
Description. The overall form of the abactinal surface was reconstructed and well described by Schondorf (1906b, fig. 16). The upper part of the abactinal surface is strongly domed (Fig. 11C; precisely as shown by Schondorf 1906b, pl. 25) and the arrangement of the ossicles is clearly shown. Twelve inner calycinal ossicles (ico) are present. The ce is small and pentagonal, and in four interradii (A-B, C-D, D-E, E-A) it articulates with a single, slightly elongated hexagonal ico. In the B-C interradius, however, it articulates with two elongated plates, and these plates and the centrale are notched to form the periproct, and the rim adjacent to the periproct is raised and thickened. The ico are proportionately small and lack spine pits. The pir are large, gently convex and heptagonal in outline, and articulate distally with two hexagonal, slightly asymmetrical plates. In the madreporic interradius, a small triangular madreporite is present (Fig. 9A) and triangular grooves adjacent to this ossicle run across the three plates. Each more distal row of interradial plates is hexagonal and these decrease in size progressively towards the ambitus. The pr (Fig. 9P, Q) are large and hexagonal, with strongly notched proximal and distal articular faces. More distal radials are also hexagonal and decrease progressively in width and proportional height towards the ambitus (Fig. 9B). The distal radials and interradials are thickened and imbricate proximally (Fig. 9C, D, G).
Differentiated marginals are not discernable in this species, nor in any other sphaerasterid, even though shown by Schondorf (1909b) in his reconstruction of this species. It was subsequently demonstrated by Hess (1991) that Schondorf’ s marginals actually belonged to the asteroid genus Asteriaceros. The interradial and radial abactinal ossicles taper distally to the ambitus, and up to 15 rows were probably present in the adult form (Fig. 11C).
The tabular, polygonal (usually hexagonal) abactinal ossicles of S. tabulatus are the most common and conspicuous elements in collections. The external surfaces of these from smaller individuals may possess an even covering of fine granule pits, which are rarely seen to carry spherical granular spines (Fig. 9L). Mature individuals carry six, or rarely more, enlarged crater-rimmed spine bases, situated adjacent to the corners of the ossicles (Fig. 9P, Q). The spines, which articulated within the pits, are rarely present in residues; these have bulbous bases and rapidly tapering, short and round shafts (Fig. 9I, J). Distal abactinal ossicles also carried irregularly developed conical and granular spines (Fig. 9C).
The first two or four papular pores adjacent to the angled margins of the large abactinal plates (Fig. 9Q) arise by division of a single internal groove that splits towards the external surface. Between five and 10 notches for papulae are present along the margins of the abactinal plates; these produce a regular crenulation to the borders of the plates (Fig. 9M, N, P, Q). The pores may be vertical or oblique in orientation when viewed laterally. The intervening articular ridges comprise simple vertical or inclined struts of stereom, but larger triangular surfaces are sometimes present in the centres of the plate sides. The narrower articular ridges each carry a single, small round concavity close to the external borders of the plates, but the larger surfaces have three or more of these structures positioned in a vertical column.
The actinal ossicles are preserved both in articulated groups and as isolated plates. They formed alternating rows of weakly imbricated, thickened ossicles which carried granular spines of diverse sizes, set in crater-like pits (Fig. 9E).
Ambulacral groove ossicles of S. tabulatus were figured by Schondorf (1906b), and new material is now known from Plettenberg (southern Germany) and Trimbach (Switzerland; H. Hess Collection, NHMB, unregistered). The adambulacrals are very tall (2–3 times taller than broad), the adradial face is convex and the abradial face is gently concave (Figs 3D–G, 7C–H). The abactinal face is approximately square, and well-defined articulation structures for the ambulacrals are present. These define the corners of the face, and ada1a and ada1b are smaller than ada2 and ada3 (Fig. 3). Clear oval insertion sites for padam and dadam muscles are present; padam is shorter and transversely broad, dadam smaller. The construction of the ambulacral-adambulacral articulation is thus typically valvatid (Gale 2011). An irregularly oval insertion site for adadm is present on the distal actinal face of the adambulacral, and a corresponding pit is present on the proximal face. The actinal, abradial margin of the adambulacral carries a row of four to five small pits for furrow spines, and on the rounded actinal portion of the external face, there are two poorly defined rows of concave attachment sites for five to six sub-adambulacral spines.
The ambulacrals are stout ossicles in which head, shaft and base are clearly distinguished (Figs 3A, H, I, 6A–D). The head is slightly asymmetrical in actinal aspect, with an enlarged proximal extension. Dentition and sites of the transverse abtam and actam are well developed, as are sites for longitudinal ambulacral structures lim and lia. The waist is slightly narrowed, and an actinal ridge separates adjacent podial basins. The base is poorly preserved on the available material, but the adradial articulation surfaces ada1a and ada2 are clear. The overall form of the ambulacral is similar to that of goniasterids and stauranderasterids (compare Fig. 3A with Fig. 4H).
Mouth frame ossicles include oral (Figs 3B, C, 8A–E) and circumoral plates (Fig. 3J, K). Small orals (Fig. 8A, B, D, E) are proportionately low, and the pb is blunt. Larger specimens (Figs 3B, C, 8C) are taller, with a proportionately large oradm and a nearly vertical orada. Well-defined oral spine (osp) sites are present. The radial face is flat (Fig. 3C) and the abactinal interradial interoral muscle (abiim) insertion site is large. The circumoral (Fig. 3J, K) is robust, with a triangular actam site, and a vertical proximal bar.
Reconstruction. Schondorf (1906b) used articulated fragments and isolated ossicles to reconstruct the overall form of S. tabulatus. However, the reconstruction of the margin and actinal surface of the species was highly inferential, and based on the interpretation of ossicles called S. pustulosus as marginals of S. tabulatus. These came from a different locality (Nattheim, southern Germany) to the other material. Schondorf (1906b) also interpreted ossicles that he called S. stellifera (Goldfuss, 1875) as worn inferomarginals of S. tabulatus. Sphaeraster stellifera was subsequently placed in Asteriaceros by Valette (1932), a genus assigned to the Stauranderasteridae by Hess (1991). None of the subsequently collected specimens of S. tabulatus (e.g. Neumann 2009) show enlarged marginal ossicles, and the new specimens figured here (Fig. 9B) definitively demonstrate that the abactinals simply decrease in size to the ambitus, without differentiated marginals (Fig. 11C).
The upper part of the body of S. tabulatus had the form of a tapered dome, as shown by Schondorf (1906b), but the articulation of the thickened, imbricating distal radials and interradials indicates outward curvature of the sides to the ambitus (Fig. 11A). The actinal ossicles indicate that the actinal surface was essentially flat, but probably curved upwards at the ambitus, as in Testudinaster. The distinction between the distalmost abactinals and lateral actinals would not be obvious.
Ontogeny. Sphaeraster tabulatus has a complex ontogeny, particularly in terms of the development of external sculpture and papular notches. The diversity of sculpture in particular led Quenstedt (1875) to coin different names (S. tabulatus juvensis, S. tabulatus and S. punctatus) for successive growth stages. Assessment of abundant new material from Plettenberg and elsewhere in southern Germany shows that all these forms intergrade continuously in an ontogenetic series, confirming the conclusions of Hess (1975). In residues from the hypsilum ammonite Subzone (Oxfordian) at Plettenberg, ossicles down to 0.5 mm are present originating in individuals with a diameter of less than 10 mm (Figs 9H, L, O, 13B–G). In contrast, large abactinal plates have a maximum dimension of 20 mm, and fully grown individuals have an estimated diameter of 300 mm. The general features of this ontogenetic series include changes in sculpture, with progressive acquisition of granular and conical spines, and the increase in number and size of papular notches.
Stage 1. Abactinal ossicle diameter 0.5– 2 mm. Abactinal ossicles (upper part of abactinal surface) carry a central area of raised anastomosing ridges and intervening pits, surrounded by a dense smooth zone of imperforate stereom, resembling a coat of glossy paint (Fig. 13B–E). The more actinally positioned ossicles are entirely smooth. No papular notches.
Stage 2. (‘ juvensis ’ form) Ossicle diameter 2–5 mm; external surface smooth, or irregularly marked with tiny pits (Fig. 9O).
Stage 3. (‘ tabulatus ’ form) Smooth, or with indistinct spine pits (Fig. 9H, L), diameter 5–10 mm.
Stage 4. (‘ punctatus ’ form) Largest abactinal ossicles carry an external sculpture comprising, typically, six large crater-rimmed spine bases adjacent to each corner of the plates. A scatter of variably sized smaller pits is commonly present on the central part of the plates (Fig. 9M, N, P, Q). The papular notches are evenly distributed along the margins of the plates (5–11 per side) and are separated by vertical to slanted articular bars.
description: Published as part of Gale, Andrew Scott, 2021, Taxonomy and phylogeny of the ' football stars' (Asteroidea, Sphaerasteridae), pp. 691-741 in Journal of Systematic Palaeontology 19 (10) on pages 704-710, DOI: 10.1080/14772019.2021.1960911, http://zenodo.org/record/10949919