Thylechinus (Thylechinus) sinaiensis, Mohamed Abdelhamid & Moustafa Azab, 2012

Mohamed Abdelhamid, Marouf Abdel-Aty & Moustafa Azab, Mahmoud, 2012, Turonian-Santonian echinoids from Egypt, Geodiversitas 34 (3), pp. 575-615 : 592

Thylechinus (Thylechinus) sinaiensis n. sp. ( Figs 8H, I; 9 B-D; 10)

HOLOTYPE. — The specimen photographed in Figure 8H, I.

MATERIAL EXAMINED. — 12 specimens, ASUAQE8-19, deposited in Geology Department, Faculty of Science, Ain Shams University, Cairo.

TYPE LOCALITY. — Wadi Abu Qaada, Central Sinai, Egypt.

STRATIGRAPHIC HORIZON. — Turonian (Wata Formation), Wadi Abu Qaada echinoid horizon 3 ( QEH 3).

ETYMOLOGY. — Named after the region of Sinai from which the material has been collected.

DIAGNOSIS. — Test round to sub-pentagonal. Adapical surface convex and convexity increases as test size increases. Adoral surface flattened. Apical disc pentagonal, caducous ( Fig. 8H). Ambulacral area wide ( Fig. 10 ), flush but feebly swollen in large-sized individuals ( Fig. 8H). Poriferous zone narrow, uniserial throughout; pore pairs arranged in triads in three plates adjacent to peristome. Interporiferous zone with two columns of imperforate, crenulated primary tubercles slightly less developed than interambulacral tubercles. On adoral and ambital areas, major ambulacral plates are composed of triads arranged in diadematoid manner ( Fig. 9C ), whereas adapically they are arranged in triads of simple plates ( Fig. 9B ). Interambulacra with two columns of imperforate, crenulated, nonconfluent tubercles. Adradial extrascrobicular surface wide and in each plate it is occupied by three mamelonated granules and many smaller granules. Interradial extrascrobicular surface relatively narrow, occupied by a lot of granules ( Fig. 9D ). Peristome round, large, flush and feebly sunken in large-sized individuals. Gill slits well developed.

MEASUREMENTS. — See Table 5.

DESCRIPTION

Poriferous zones uniserial throughout. Major ambulacral plates are composed of triads ( Fig.9B, C ). Both ambulacral and interambulacral tubercles imperforate, crenulated, and nonconfluent. Adradial extrascrobicular surface wide, and occupied by three mamelonated granules, and many smaller granules on each plate ( Fig. 9D ).

REMARKS

The present species has uniserial poriferous zones throughout, trigeminate major ambulacral plates ( Fig. 9B, C ), both ambulacral and interambulacral areas with only two columns of imperforate, crenulated primary tubercles, and no large secondary tubercles. These characters refer the present species to the subgenus Thylechinus (Thylechinus) . The present material is distinguished from T. (T.) arabicus ( Fourtau, 1912) in having larger peristome (Dp/D = 0.30 in the latter species), wider ambulacra (Wa/Wi = 0.50 in the latter species) and wider extrascrobicular surface occupied by a lot of well-developed granules. It is distinguished from T (T.) ioudi (Péron & Gauthier, 1881) from the Campanian of Algeria in having large, pentagonal apical disc (it is small, round in the latter species), adoral and ambital interambulacral tubercles separated by a horizontal series of granules (scrobicules are tangent in the latter species), and granules on adradial extrascrobicular surface are fairly more developed than those on interradial extrascrobicular surface (they are homogeneous in the latter species). It is distinguished from T. (T.) said (Péron & Gauthier, 1881) by its nonconfluent interambulacral tubercles, larger apical disc (La/D = 0.34 in the latter species), larger peristome (Dp/D = 0.39 in the latter species), and in having relatively more flattened test (H/D = 0.46-0.63 in the latter species). Thylechinus (T.) schlumbergeri (Cotteau, 1864) from the Turonian of Batna and Martigues is distinguished from the present material by the abundance of granules on interambulacrals and separation of all its ambulacral tubercles by a double horizontal series of granules. T. (T.) simplex Thomas & Gauthier, 1889 is distinguished from the present material by its smaller peristome (Dp/D = 0.36-0.40 in T. (T.) simplex) and its ambulacral tubercles are smaller than interambulacral tubercles and strongly reduced in size adapically.

Figures

FIG. 9. — Camera lucida drawings: A, plating, tuberculation and poring of subambital ambulacrum in Phymosoma thevestense (Péron & Gauthier, 1879) from the Coniacian-Santonian of Abu Roash; B-D, plating, tuberculation and poring in Thylechinus (T.) sinaiensis n. sp. from the Turonian of Wadi Abu Qaada; B, adapical ambulacrum; C, ambital ambulacral plates; D, subambital interambulacral plates; E-G, plating, tuberculation and poring in Thylechinus (O.) quincuncialis Gregory, 1906 from the Turonian of Wadi Abu Qaada; E, ambital interambulacral plate; F, adapical ambulacrum; G, ambital ambulacrum. Scale bars: A, B, 0.5 mm; C, 0.4 mm; D, 0.8 mm; E, 2 mm; F, 0.9 mm; G, 1 mm.

FIG. 10. — Biometric data on Thylechinus (T.) sinaiensis n. sp. showing the relation between: test diameter and test height (H); test diameter and both of width of ambulacrum (Wa, filled quadrangles, solid line) and width of interambulacrum (Wi, empty quadrangles, dashed line); test diameter and each of number ambulacral tubercles per row (Na, filled quadrangles, solid line) and number of interambulacral tubercles per row (Ni, empty quadrangles, dashed line); test diameter and each of diameter of peristome (Dp, filled quadrangles, solid line) and length of apical system (Ls, empty quadrangles, dashed line).