Macandrevia tenera ( Jeffreys, 1876a )

Hansen, Jesper, 2024, Brachiopods of the Norwegian fauna northern North Atlantic and Arctic, with a focus on, Fauna norvegica 43, pp. 12-68 : 41

Macandrevia tenera ( Jeffreys, 1876a)

Figures 32 , 33

Terebratula tenera Jeffreys, 1876a, p. 250 .

Terebratula (Waldheimia) tenera – Jeffreys (1878), p. 405, pl. 22, fig. 7.

Waldheimia (Macandrevia) tenera – Davidson (1886), p. 66, pl. 12, figs. 6–10.

Macandrevia tenera – Beecher (1893), p. 396, pl. 1, fig. H2.

Description: Compressed equi- to ventribiconvex shell with L/W ratio 1.06–1.43. Outline typically slightly truncated, elongate and egg-shaped, but smaller specimens and occasionally larger specimens are broad and egg-shaped. Dorsal valve usually longer than wide. Shell fragile and rather dull. Ventral umbo small, less prominent and more delicate than that of Macandrevia cranium . Anterior commissure rectimarginate. Deltidial plates rudimentary, bordering moderately sized and elongate pedicle opening. Ridges bordering deltidial plates hardly developed. Ornamentation lacking except for weak growth lines, which are more distinct than those of M. cranium . Shell matrix densely endopunctate. Colour light yellowish-brown. Hinge teeth in ventral valve high, but delicate and supported by short dental plates. Brachial loop in dorsal valve narrow and horseshoe-shaped. Cardinal process is a short ridge between socket ridges and attached directly to valve floor. Small specimens with a short but high septum centred at approximately 2/5 valve length. Largest specimen 13 mm long and 10 mm wide.

Depth range: 207–2652 m ( Jeffreys 1876a,b; Cooper 1973a).

Temperature range: Based on four stations, the range is 1.6– 4.5˚C (this study).

Salinity range: Based on three stations, the range is 34.96–35.33 (this study).

Substrate: Globigerina ooze with stones ( Jeffreys 1876a). Specimens are found attached to gravel.

Geography: NW North Atlantic, Labrador in Canada, and S Greenland ( Jeffreys 1876a; Cooper 1973a). A ‘recently dead’ specimen collected NW of Ireland was also assigned to this species by Brand et al. (2003).

Figures

Figure 32. Macandrevia tenera. a–d: dorsal, ventral, lateral and anterior views of specimen attached to gravel, Denmark Strait, E Greenland, the ‘Ingolf’ 1895 expedition st. 91, 2328 m, Zoological Museum of Copenhagen; e–f: interior view of dorsal and ventral valve of specimen, Denmark Strait, E Greenland, the ‘Ingolf’ 1895 expedition st. 91, 2328 m, Zoological Museum of Copenhagen; g: lateral view of specimen from batch NHMD-1201197, Irminger Sea, 2448 m; h–i: dorsal and anterolateral views of shell from batch NHMD-1201197, Irminger Sea, 2448 m; j: Dorsal view of specimen NHMD-1201195, W Greenland, mouth of Ameralik Fjord; k–l: dorsal views of two shells from batch NHMD-1201197, Irminger Sea, 2448 m; m: interior view of ventral valve from batch NHMD-1201197, Irminger Sea, 2448 m. Scalebar 1mm. Photos: Jesper Hansen.

Figure 33. Distribution of Macandrevia tenera.