Phymosoma beadnelli ( Gregory, 1906 )

Mohamed Abdelhamid, Marouf Abdel-Aty & Moustafa Azab, Mahmoud, 2012, Turonian-Santonian echinoids from Egypt, Geodiversitas 34 (3), pp. 575-615 : 586

Phymosoma beadnelli ( Gregory, 1906) ( Figs 5J; 7C, D )

Cyphosoma beadnelli Gregory, 1906: 221 , pl. 10, figs 6-8.

Cyphosoma abbatei mutatio beadnelli – Fourtau 1914: 29.

Phymosoma beadnelli – Devriès 1960: 133.

MATERIAL EXAMINED. — Many deformed tests and numerous test fragments from the Coniacian-Santonian of Abu Roash (Ostrea and Plicatula unit), ASUARE41-43, Abu Roash echinoid horizon 4 ( REH 4).

DESCRIPTION

Test with medium to large size. Ambulacral area wide (Wa/Wi = 0.79). Poriferous zone shows conspicuous biserial arrangement from the ambitus to the apex, wide near the apex where the two poriferous zones constitute 64% of ambulacrum width. At the ambitus and adoral surface, ambulacral primary tubercles are confluent and as large as interambulacral tubercles but decrease in size near the apex.

REMARKS

The present species is distinguished from P. abbatei in having confluent ambulacral and interambulacral tubercles, conspicuous biserial arrangement of poriferous zones above ambitus ( Fig. 7C, D ), and wider ambulacra (Wa/Wi = 0.79 vs 0.62-0.72). It is distinguished from P. baylei (Cotteau, 1864) in having wider ambulacra (Wa/Wi = 0.79 vs 0.63- 0.73 in the latter species) and confluent ambulacral and interambulacral tubercles. Fourtau (1921) considered P. beadnelli as a mutation from P. abbatei , but it is believed that the above-mentioned differences between the two forms are sufficient to consider them separate species. Devriès (1960) pointed out that P. beadnelli resembles P. coquandi (Cotteau, 1864) but the latter species is distinguished in having wider extrascrobicular surface, nonconfluent areoles and abundant granules on interambulacra.

Figures

FIG. 7. — Camera lucida drawings: A, B, plating, tuberculation and poring in Phymosoma baylei (Cotteau, 1864) from the Turonian of Wadi Abu Qaada; A, ambital ambulacral plates; B, ambital interambulacral plate; C, D, plating, tuberculation and poring in Phymosoma beadnelli (Gregory, 1906) from the Coniacian-Santonian of Abu Roash; C, adapical ambulacral plates; D, ambital interambulacral plates; E, F, plating, tuberculation and poring in Phymosoma thevestense (Péron & Gauthier, 1879) from the Coniacian-Santonian of Abu Roash; E, ambital interambulacral plates; F, subambital ambulacral plates; G, plating and tuberculation of ambital interambulacral plates in Rachiosoma irregulare Fourtau, 1921 from the Turonian of Wadi Abu Qaada. Scale bars: A, 0.8 mm; B, 0.9 mm; C, D, 1 mm; E, F, 0.5 mm; G, 0.7 mm.