Testudinaster peregrinus Hess, 1983

Gale, Andrew Scott, 2021, Taxonomy and phylogeny of the ‘ football stars’ (Asteroidea, Sphaerasteridae), Journal of Systematic Palaeontology 19 (10), pp. 691-741 : 721-725

Testudinaster peregrinus Hess, 1983

( Fig. 21A–C )

$1983 Testudinaster peregrinus Hess : 921, pl. 1, figs 1–3.

1994 Testudinaster peregrinus Hess ; Hess: 988, figs 1, 2.

Type. The holotype ( Fig. 21A, B ; NMB M 9689 ), showing a partial abactinal surface, is from Schinznach, in the northern Swiss Jura (the original of Hess, 1983, pl. 1, figs 1–3) .

Material. Three specimens from the upper Bajocian (upper Hauptrogenstein), Switzerland. Two further specimens showing the actinal surface come from the same formation and age, at Auenstein (Canton of Aargau; NMB M 9923 ), as figured by Hess (1994, figs 1, 2) .

Description. The external morphology of T. peregrinus is almost completely known on the basis of two specimens showing, respectively, the actinal ( NMB M 9923) and abactinal ( NMB M 9689) surfaces ( Hess 1983, 1994). The specimens are crushed abactinally-actinally, but can be reconstructed by the use of displaced ossicle articulations. The abactinal surface was originally hemispherical, and the outer actinal surface slightly inflated. The central part of the actinal surface was flat. Extensive dislocation and displacement of actinal ossicles along the ambitus was a result of postmortem collapse of an inflated body form ( NMB M 9923). The adambulacral ossicles have small, square actinal surfaces, and fit together closely, tightly covering the groove. The actinal ossicles are small and massive, very numerous, and arranged in a chevron pattern, ‘V’-ing towards the peristome. The proximal actinals are more irregular in distribution and approximately rhombic in outline. The more distal actinals, towards the ambitus, form discrete transverse rows of elongated, rectangular plates, which form a bowed double arc, symmetrical about the interradius. Displaced ossicles show that the ambital actinals are taller than long and formed a thick body wall.

The abactinal surface is divided into a central area and well-demarcated distal radial regions. The central area is a tesselation of numerous (over 100) evenly sized but irregularly shaped polygonal abactinal ossicles. These are relatively thin (maximum dimension 2–3 times height), and the margins are notched by two to four papular pores along each articular surface. The primary abactinal ossicles cannot be identified with certainty. The distal radial regions are made up of sub-parallel, well-defined rows of short, broad ossicles, which narrow distally, in which direction the ossicles also become shorter and taller. The radial row is symmetrical along the radius, and the ossicles are slightly concavo-convex (distal-proximal). The external surface of all abactinal ossicles appears to be smooth.

Remarks. Although originally assigned provisionally to the Asterinidae Gray, 1840 by Hess (1983), T. peregrinus was subsequently linked to the Sphaerasteridae on the similarity of body form and the tabular abactinal ossicles with conspicuous papular pores ( Hess 1994). However, the absence of large marginals in Testudinaster comparable with those in Schondorf’ s (1906b) reconstruction of the species S. tabulatus made Hess wary of the relationship. The discovery that the large marginals in S. tabulatus are a result of imaginative reconstruction, and are not actually present, brings Testudinaster closer to S. tabulatus . It differs from that species in the more numerous abactinal plates of the dorsal surface and the development of rows of abactinals towards the ambitus ( Fig. 21A ). Additionally, the plates of the actinal surface are very numerous and elongated ( Fig. 21C ).

Figures

Figure 21. Testudinaster peregrinus Hess, 1983. A, holotype, abactinal view, upper Hauptrogenstein (upper Bajocian), Schinznach, Switzerland (NMB M 9689); B, interpretative drawing, colours as in Figure 1; C, actinal view of another specimen, upper Hauptrogenstein (upper Bajocian), Auenstein, Canton of Aargau, Switzerland (NMB M 9923). Scale bars = 10 mm.