Petraster kinahani ( Baily, 1879 )

Blake, Daniel B. & Lefebvre, Bertrand, 2024, Ordovician Petraster Billings, 1858 (Asteroidea: Echinodermata) and early asteroid skeletal differentiation, Comptes Rendus Palevol 23 (17), pp. 217-239 : 224

Petraster kinahani ( Baily, 1879)

( Figs 5; 6)

Palasterina kinahani Baily, 1879: 56 , fig. 6.

Uranaster kinahani – Gregory 1899: 348. — Schöndorf 1910: 225. — Schuchert 1915: 155. — Spencer 1916: 105. — Owen 1965: 567.

Petraster kinahani – Spencer & Wright 1966: 43, fig. 43.4. — Dean Shackleton 2005: 91, pl. 6, figs 5, 6; fig. 12C. — Blake 2018: pl. 2, fig. 16; pl. 5, figs 1, 2.

DIAGNOSIS. — Arms proportionately elongate, tapering evenly. Aboral ossicles uniform, equidimensional, closely fitted; carinal, adradialia not definitively recognized; intercalated accessories not recognized. Two enclosed axillaries present, disk actinal field large. Axials rectangular, transverse ridge “L” shaped.

MATERIAL EXAMINED. — Latex casts of approximately 20 specimens, many fragmentary, poorly preserved; Geological Survey of Ireland, Natural History Museum, London.

TYPE LOCALITY AND HORIZON. — Ballymoney Group (Sandbian; see Donovan et al. 1996), near Bannow, County Wexford, Ireland .

DESCRIPTION

Petraster in which arms are relatively elongate, R reaching at least c. 35 mm. Aboral ossicular series of arms approximately equidimensional and closely fitted; smaller accessories not recognized. Carinal series differentiation suggested by some weak alignment; adradialia not recognized. Madreporite on aboral disk of larger specimens bordered laterally by enlarged, crescentic ossicles. Enlarged, subcircular, aligned ossicles lateral to arm midline recognized as superomarginal, series differentiation weakening on disk. Inferomarginals robust, approximately equidimensional, weakly increasing in size on disk. Intermarginals present but irregularity of size and alignment obscures delineation.Axillaries represented by two approximately elliptical ossicles, the more distal small, abutting inferomarginal series. Actinal definition poorly known, actinals restricted to disk, proximal arms appearing small, equidimensional, irregular.

Axials approximately equidimensional, sequential axials abutted, not overlapping; transverse ridge broadly J-shaped, transverse channel well-defined. MAO pair narrow, circumorals not thought to be dumbbell shaped. Adaxials with prominent “nose” articulating with axial. Adaxials possibly elliptical, longitudinally elongate prominent nose developed.

REMARKS

Petraster kinahani is separated from P. caidramiensis n. sp. and P. crozonensis by presence of distal abactinal arm ossicles that lack clear differentiation in form or into series; the absence of aboral intercalated granular accessories; the irregular arrangement of proximal superomarginals and intermarginals; the complex, multiossicular oral disk ossicular configuration with two axillaries; and equidimensional abutted axials with a “J”- shaped transverse ridge.

A small ambulacral area ( Fig. 6A 1) is problematic. One area (horizontal arrow to upper left) shows a series of five axial transverse ridges offset from prominent noses of adaxials, the displacement accompanying sediment compaction, whereas another area (inclined arrow to lower left) suggests a series of five separate small ossicles between the axials and adaxials. Presence of an “extra” ossicle emplaced between the axial and adaxial is diagnostic of the Stenuroidea ( Blake 2013). A similar expression was found in none of the other specimens of P. kinahani , the interval to lower left interpreted as preservational aberrancy while recognizing the occurrence might reflect paraphyly or polyphyly of the stenuroid condition.