Argyrotheca jacksoni Cooper, 1973

Bitner, Maria Aleksandra & Logan, Alan, 2016, Recent Brachiopoda from the Mozambique-Madagascar area, western Indian Ocean, Zoosystema 38 (1), pp. 5-41 : 24-26

Argyrotheca jacksoni Cooper, 1973

( Fig. 14K, L )

Argyrotheca jacksoni Cooper, 1973a: 17 , pl. 3, figs 9-13. — Bitner et al. 2008: 282-284, fig. 3A-K. — Logan et al. 2008: 303. fig. 3G-O. — Zezina 2010: 1191. — Logan & Bitner 2013: 169-171, fig. 6A-M.

Argyrotheca australis – Zezina 1987: 558.

Argyrotheca sp. — Hiller 1994: 784, fig. 12.8-12.9.

MATERIAL EXAMINED. — South Madagascar. ATIMO VATAE, stn CP 3615, 1 bivalved specimen, 1 ventral valve.

DEPTH RANGE. — 284- 286 m.

MEASUREMENTS. — Length 1.6 mm, width 1.9 mm, thickness 1.0 mm; length 1.8 mm, width 2.4 mm.

REMARKS

This species is characterized by its thin shell, small size (length of ventral valve rarely exceeding 2 mm) and numerous, shallowly rounded ribs. The investigated specimens are consistent with specimens of this species recorded by Cooper (1973a), Logan et al. (2008) and Logan & Bitner (2013) from the Red Sea. The specimens of A. jacksoni described from the Persian Gulf ( Bitner et al. 2008) differ slightly from those studied here and in the Red Sea in having more marked ribs. In outline and ornamentation the specimens from Madagascar are similar to A. cuneata (Risso, 1826) from the Mediterranean Sea, but lack the pink-red wash between the costae which is characteristic of that species.

The studied specimens differ strongly from another Argyrotheca species described from this region, A. angulata Zezina, 1987 , in outline and ornamentation. A. angulata is very transversely elongate (see below) and its shell is nearly smooth, having only four fine radial lines ( Zezina 1987).

Figures

FIG. 14. — A-J, Argyrotheca cf. angulata Zezina, 1987, North-West Madagascar, West of Cap d’Ambre, MIRIKY, stn DW 3199, 527-652 m: A-E, complete specimen (MNHN IB-2013-80), dorsal view (A); B-E, inner,oblique, tilted anterior views of dorsal valve, and enlargement (E) of septum and lateral outgrowths; F, inner view of ventral valve; G-J, complete specimen (MNHN IB-2013-81), dorsal view (G) and enlargement of umbonal part to show details of the beak; I, J, inner view of dorsal valve and enlargement (J) of tilted anterior view to show the prong; K, L, Argyrotheca jacksoni Cooper, 1973, South Madagascar, South Cap Sainte Marie, ATIMO VATAE, stn CP 3615, 284-286 m: K, inner of view of ventral valve (MNHN IB-2013-82); L, dorsal view of complete specimen (MNHN IB-2013-83). All SEMs. Scale bars: A-C, F-I, 1 mm; D, K, L, 500 µm; E, J, 200 µm.