Gryphus sp.

Bitner, Maria Aleksandra & Moissette, Pierre, 2003, Pliocene brachiopods from north-western Africa, Geodiversitas 25 (3), pp. 463-479 : 471-472

Gryphus sp. ( Figs 4 M-O; 5A, B; Table 5)

MATERIAL EXAMINED. — Three complete specimens from Algeria: LP-MNHN B.38666, B.38671 (see also Table 1).

OCCURRENCE. — The genus Gryphus is known from the Eocene to the Recent. From the Pliocene it is recorded from Italy and Spain. Today it lives in the Mediterranean Sea and the Atlantic Ocean at depths from 70 to 2663 m.

DESCRIPTION

The small shell is elongate, biconvex and smooth except for numerous distinct growth lines. The lateral commissure is straight or nearly straight, and the anterior commissure is rectimarginate. The beak is short, suberect to erect, truncated by a small, epithyrid foramen. Deltidial plates conjunct forming a partially visible symphytium. Internal characters unknown.

The shell displays ultrastructure typical of the genus Gryphus , i.e. composed of three layers ( Fig. 5A, B ) ( MacKinnon & Williams 1974; Taddei Ruggiero 1983; Gaetani & Saccà 1984, 1985a; Benigni 1985). The primary granular layer is thin (14-25 µm thick) and built of acicular crystallites perpendicular to the shell surface. The secondary fibrous layer is 25-42 µm thick. The fibres are well developed, 11.2-12.7 µm wide and 3.4-3.7 µm thick. They are of anvil-like shape, arranged in sheaves nearly parallel to the surface of the shell. Around each punctum the fibres are deflected outwards ( Fig. 5B ). The tertiary layer is much thicker (63-87 µm) than the first two layers and is made up of large calcitic prisms perpendicular to the shell surface. The total thickness of the shell is 111-145 µm.

REMARKS

The investigated material is limited and the specimens are damaged and/or crushed, making measurements difficult. Externally, the specimens display characters consistent with those given in the diagnosis of the genus Gryphu s ( Cooper 1983), as does the presence of the tertiary prismatic layer. The tertiary layer, if present, is considered as a diagnostic generic character because it occurs in all species of a genus ( MacKinnon & Williams 1974; Taddei Ruggiero 1983; Gaetani & Saccà 1984, 1985a; Benigni 1985) and enables the genera Terebratula and Gryphus to be readily distinguished.

The specimens under study differ strongly from the Pliocene species G. sphenoideus (Philippi, 1844) which is much larger and has a large foramen ( Gaetani & Saccà 1984, 1985a). In size the specimens are similar to G. minor ( Philippi, 1836) , another Pliocene species, differing in shell outline and smaller foramen ( Gaetani & Saccà 1985a).

This is the first record of Gryphus from North Africa.

Figures

FIG. 4. — A-L, Terebratula sp., ventral, dorsal, lateral and anterior views of complete specimens, Had Mramer, Morocco (LP-MNHN B.38316); M-O, Gryphus sp.; M, N, dorsal and lateral views of complete specimen, Mustapha inférieur (Algiers), Algeria (LP-MNHN B.38671); O, dorsal view of complete specimen, Aïn Benian, Algeria (LP-MNHN B.38666). Scale bars: A-L, 1 cm; M-O, 5 mm.

FIG. 5. — A, B, Gryphus sp. (LP-MNHN B.38671), SEM micrographs; A, transverse section of the entire shell showing the acicular primary layer (top) underlain by the secondary layer of anvil-shaped fibres, passing into the prismatic tertiary layer; B, section of the shell showing two puncta filled with pyrites, fibres near the canals bent outward; C, D, Terebratula sp. (LP-MNHN B.38316), SEM micrographs; C, transverse section of the shell showing the boundary of the acicular primary and fibrous secondary layers; D, section of the secondary layer showing fibres in oblique and longitudinal section, visible (left) modification of fibres near a punctum. Scale bars: 20 µm.