Phymosoma roachensis ( Fourtau, 1914 )

Mohamed Abdelhamid, Marouf Abdel-Aty & Moustafa Azab, Mahmoud, 2012, Turonian-Santonian echinoids from Egypt, Geodiversitas 34 (3), pp. 575-615 : 588-590

Phymosoma roachensis ( Fourtau, 1914) ( Fig. 8A, B)

Cyphosoma roachense Fourtau, 1914: 33 , pl. 3, fig. 3.

Phymosoma roachensis – Abdelhamid 1997: 143, fig.5 (4).

MATERIAL EXAMINED. — Six specimens from the Coniacian-Santonian of Abu Roash (Ostrea and Plicatula unit), ASUARE44-49, Abu Roash echinoid horizon 4 ( REH 4).

MEASUREMENTS. — See Table 2.

DESCRIPTION

Test very small, discoidal, low. Both adapical and adoral surfaces flattened. Outline of apical disc large, sub-round. Poriferous zones biserial near apical disc. Major ambulacral plates trigeminate near peristome, quadrigeminate at the ambitus and adapically. Interambulacral area with four columns of imperforate, crenulated primary tubercles. Peristome not sunken, large.

REMARKS

The present species is distinguished from the previously mentioned species of Phymosoma , in the present work, in having very small, discoidal and low test; flattened adapical and adoral surfaces, and not sunken peristome.

Phymosoma thevestense (Péron & Gauthier, 1879) ( Figs 7E, F ; 8C, D; 9A )

Cyphosoma thevestense Péron & Gauthier in Cotteau, Péron & Gauthier, 1879: 105, pl. 8, figs 5-8.

Phymosoma thevestense – Abdelhamid & El Qot 2001: 14, fig. 5A.

MATERIAL EXAMINED. — Six measured specimens and numerous non-measured ones from the Coniacian- Santonian of Abu Roash (Ostrea and Plicatula unit), ASUARE50-55, Abu Roash echinoid horizon 4 ( REH 4).

MEASUREMENTS. — See Table 3.

DESCRIPTION

Test low, discoidal ( Fig. 8D). Adoral surface flattened, slightly depressed around peristome. Adapical surface flattened to feebly convex. Ambulacral area wide. Poriferous zones biserial near apical disc ( Fig. 8C). Major ambulacral plates polygeminate with four to five pore pairs at the ambitus and adapically ( Figs7F ; 9A ), trigeminate near peristome. Interambulacral area with two columns of imperforate, crenulated primary tubercles.Two columns of granules occur around the interradial suture, and one column near the adradial suture ( Fig.7E ).

REMARKS

The present species is distinguished from Phymosoma major and Phymosoma roachensis ( Fourtau, 1914) in having two columns of primary tubercles on each interambulacrum. It is distinguished from Phymosoma abbatei in having conspicuous biserial poriferous zones adapically, larger apical disc (Ls/D = 0.80 against 0.37-0.42 in Phymosoma abbatei ), wider ambulacra (Wa/Wi = 0.68-0.80 against 0.62- 0.72 in Phymosoma abbatei ) and in having narrower extrascrobicular surface. It is distinguished from Phymosoma baylei in having smaller test (D = 11.2-19.3 mm vs 24.5-30.0 mm in Phymosoma baylei ), wider ambulacra (Wa/Wi = 0.68-0.80 vs 0.63-0.73 in Phymosoma baylei ) and in having narrower extrascrobicular surface. In Phymosoma beadnelli , the poriferous zones show conspicuous biserial arrangement from the ambitus to the apex, wide near the apex, where the two poriferous zones constitute 64% of ambulacrum width, the primary tubercles are confluent at the ambitus and adoral surface, and this distinguished it from the present species. The present species is recorded from the Turonian of Algeria and Tunisia, but in Egypt it occurs in the Coniacian-Santonian.

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.

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.