Phymosoma abbatei (Gauthier, 1898)

Mohamed Abdelhamid, Marouf Abdel-Aty & Moustafa Azab, Mahmoud, 2012, Turonian-Santonian echinoids from Egypt, Geodiversitas 34 (3), pp. 575-615 : 584

Phymosoma abbatei (Gauthier, 1898) ( Figs 5G, H; 6E, F )

Cyphosoma abbatei Gauthier in Fourtau, 1898: 620, pl. 1, figs 2-6.

Phymosoma abbatei – Abdelhamid & El Qot 2001: 13, fig.4J, K. — Abdallah et al. 2001: pl. 3, fig. 12. — El Qot 2006: 134, pl. 31, figs 1, 2, 4.

MATERIAL EXAMINED. — 31 measured specimens and numerous non-measured from the Turonian of Abu Roash (rudist unit), ASUARE10-40, Abu Roash echinoid horizon 1 ( REH 1).

MEASUREMENTS. — See Table 1.

DESCRIPTION

Test rounded, low. Adapical surface flattened to slightly convex. Adoral surface not sunken around peristome. Outline of apical system large, pentagonal and caducous ( Fig.5G). Ambulacral area wide, narrower adapically than near peristome. Poriferous zones undulate adapically, biserial near apical disc (uniserial in some specimens). Interporiferous zone with two columns of imperforate, crenulated primary tubercles as large as interambulacral tubercles at the ambitus and peristome, but tubercles very small and wide apart adapically ( Fig. 6E, F ). REMARKS

Fourtau (1914) pointed out that the uniserial arrangement of the poriferous zones of the present species is confined to small individuals (diameter less than 16 mm). In the present material, it was found that the poriferous zones show variable arrangements, as in some specimens the biserial arrangement is conspicuous; in others, the biserial arrangement is confined to some ambulacral areas or even to some poriferous zones. It is worth mentioning that most of the large-sized specimens have biserial poriferous zones.

Figures

FIG. 6. — Camera lucida drawings: A, B, plating, tuberculation and poring of ambital interambulacral plates (A) and ambital ambulacral plates (B) in Orthopsis miliaris (d’Archiac, 1835) from the Coniacian-Santonian of Abu Roash; C, D, plating, tuberculation and poring of ambital interambulacral plates (C) and ambital ambulacral plates (D) in Orthopsis ovata (Coquand, 1862) from the Turonian of Wadi Abu Qaada; E, F, plating, tuberculation and poring in Phymosoma abbatei (Gauthier, 1898) from the rudist unit of Abu Roash; E, adapical half ambulacrum; F, adoral half interambulacrum and half ambulacrum; G, plating, tuberculation and poring of adapical half ambulacrum in Phymosoma baylei (Cotteau, 1864) from the Turonian of Wadi Abu Qaada. Scale bars: A, 0.4 mm; B, 0.3 mm; C, D, 1 mm; E, F, 0.8 mm; G, 0.4 mm.