Alkaidia sumralli Blake & Reid, 1998

Gale, Andy S. & Jagt, John W. M., 2021, The fossil record of the family Benthopectinidae (Echinodermata, Asteroidea), a reappraisal, European Journal of Taxonomy 755, pp. 149-190 : 183-186

Alkaidia sumralli Blake & Reid, 1998

Figs 16A–C , 17B–E, H, K

Alkaidia sumralli Blake & Reid, 1998: 529 , fig. 9/1–14.

Alkaidia sumralli – Ewin & Gale 2020: 13, figs 10.1–10.2, 13.3, 13.8, 13.11–13.12.

Diagnosis

Alkaidia in which the primary radial ossicles are elongated and the terminal ossicle is not deeply notched on its proximal margin.

Material examined

The holotype (Texas Memorial Museum, number 1786 TX1) is from the Grayson Formation (lower Cenomanian) at the Waco shale pit (Waco, Mclennan County, Texas, USA).Additional material comprises a magnificent individual ( NHMUK PI EE 15225 ), collected by Frank Holterhoff from the Grayson Formation (lower Cenomanian) of Dottie Lynn, Fort Worth, Texas and illustrated here ( Fig. 16A–C ), as well as numerous dissociated ossicles from the same locality ( NHMUK PI EE 18005–18007 , 18009 ) .

Remarks

The affinities of A. sumralli have recently been discussed in some detail by Ewin & Gale (2020) and the evidence for its inclusion in the Forcipulatida (Zorocallina) and the family Terminasteridae can be summarised briefly as follows: the presence of abundant, straight ‘duck-billed’ forcipulate pedicellariae is a characteristic of the Zorocallina ( Fig. 16D ); the construction of the abactinal surface is closely similar to that of zoroasterids and terminasterids, which also have large, Y-shaped first superomarginals and a row of robust, lobed, quadrangular radial ossicles which imbricate proximally and each carry a centrally placed conical spine ( Ewin & Gale 2020).

Additionally, the morphology of the adambulacrals and ambulacrals, and the nature of their articulation is similar in zoroasterids, Terminaster and Alkaidia ( Fig. 17 ). Ada1a and ada2 are concave on the adamulacrals ( Fig. 17A–C ) and positioned on a process on the ambulacrals ( Fig. 17G–H, J–K ). The dadam and padam facets are subequal in size, broad and short ( Fig. 17A–C ).

The abactinal construction is never seen in extant benthopectinids, in which the abactinal ossicles in the arms are small and parapaxilliform or very small, and never imbricate. Additionally, in benthopectinids the abactinal surface is invariably flat, and the arm section is not subcylindrical.

Figures

Fig. 16. A–C. Alkaidia sumralli Blake & Reid, 1998 (NHMUK EE15225). A–B. Abactinal (A) and actinal (B) views of well-preserved individual, retaining spines and pedicellariae. C. Enlargement of ambulacral groove, showing spines and duck-bill pedicellariae. — D. Zoroaster fulgens Thomson, 1873, duck-billed pedicellaria of a zoroasterid (A.S. Gale collection, unregistered). Provenance:A–C. Grayson Formation, Graysonites wacoense ammonite Zone, Dottie Lynn Lane, Fort Worth, Texas, USA (for details of locality, reference is made to Hess 2015 and Gale et al. 2021). D. Recent, Rockall Trough, northeast Atlantic. Scale bars: A–B = 50 mm; C = 5 mm; D = 0.5 mm.

Fig. 17.A, F–G. Zoroaster fulgensThomson, 1873 (A.S. Gale collection, unregistered). A.Adambulacral, in abactinal view; the original of Gale (2011a: pl. 8 fig. 5). F. Ambulacral base, in actinal view; the original of Gale (2011a: pl. 8 fig. 8). G. Ambulacral, in proximal view. — B–E, H, K. Alkaidia sumralli Blake & Reid, 1998, isolated ambulacrals and adambulacrals. B–C. Abactinal views of adambulacrals (NHMUK PI EE 18005–18006). D. Abactinal view of ambulacral (NHMUK PI EE 18007). E. Actinal view of adambulacral (NHMUK PI EE 18008). H. Actinal view of ambulacral (NHMUK PI EE 18008). K. Proximal view of ambulacral (NHMUK PI EE 18010), the original of Gale (2011a: pl. 8 fig. 9). — I–J. Terminaster cancriformis (Quenstedt, 1876) (NMB M 9036), ambulacral, in abactinal and actinal views; the original of Gale (2011a: pl. 26 figs 11–12). Provenance: A, F–G. Recent, Rockall Trough, northeast Atlantic. B–E, H, K. Grayson Formation, Graysonites wacoense ammonite Zone, Dottie Lynn Lane, Fort Worth, Texas, USA (for locality details, reference is made to Hess 2015 and Gale et al. 2021). I–J. Upper Oxfordian (Couches d’Effingen, bifurcatus ammonite Zone, stenocycloides ammonite Subzone), Savigna, near Orgelet, Département de Jura, France (Gale 2011b). See Material and methods for abbreviations. Scale bars: 1 mm.