Sphaerasteridae Schondorf, 1906a

Gale, Andrew Scott, 2021, Taxonomy and phylogeny of the ‘ football stars’ (Asteroidea, Sphaerasteridae), Journal of Systematic Palaeontology 19 (10), pp. 691-741 : 702

Family Sphaerasteridae Schondorf, 1906a

Diagnosis. A group of asteroids with spherical to sub-spherical body form, in which the abactinal surface is strongly domed and made up of relatively few, large, polygonal abactinal and actinal ossicles. Marginals are not differentiated. Primary (extra-ambulacral groove) ossicles are tabular to sub-conical in form. Adambulacral-ambulacral articulations and inter-adambulacral contacts have cavities for probable attachment of ligaments. The primary ossicles are made up of three discrete stereom layers: an external one of dense perforate stereom, a middle one of rectilinear stereom and an internal one of labyrinthic material.

Remarks. Ossicle material that was described as a stauranderasterid, Poncetaster crateri , by Villier et al. (2004b), characterized by crater-shaped spine pits, appears to be an actinal ossicle of an indeterminate sphaerasterid; this sculpture is widespread in sphaerasterids. The family Podosphaerasteridae Fujita & Rowe, 2002 is synonymized with Sphaerasteridae because the only significant supposed morphological difference, the presence of large marginal plates in the latter family, does not exist. The detailed ossicular homologies between Podosphaeraster and fossil sphaerasterids (e.g. Figs 1 , 2 ) outlined in this paper support this position, and the very close relationship between Podosphaeraster and Valettaster (Bremer support of 5, Fig. 4 ) extends to details of many ossicle types, including orals and abactinals.

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 2. Homology of primary abactinal plates in valvatidan asteroids. A, Manfredaster bulbiferus (Forbes, 1848), Stauranderasteridae; B, Sphaeraster tabulatus (Goldfuss, 1833), Sphaerasteridae; C, Echinosphaeraster (gen. nov.) scutatus (Goldfuss, 1833), Sphaerasteridae; D, Nymphaster arenatus (Perrier, 1881), Goniasteridae; E, Podosphaeraster pulvinatus Rowe & Nichols, 1980, Podosphaerasteridae. Colours as in Figure 1.

Figure 4. Cladogram of possible relationships of sphaerasterids and podosphaerasterids; a consensus tree based on a heuristic analysis of 30 characters (Supplemental material, Tables S1, S2), with support values given (Bremer/bootstrap).