(Jones and Brady, 1865)
Non-spinose, very low trochospiral, large (>1 mm), flat on both sides, with 5-6 chambers in last whorl. With prominent keel (may be fimbriated), and broad lip over umbilical-extraumbilical aperture. Sutures straight on apertural side, curved on spiral side. Pustules thick on older chambers and in front of aperture, smaller towards periphery and on younger chambers. Calcite crust often visible, growing like pustules from older to younger parts of test.
Ref.: Scott (1973), Adelseck (1975), Hemleben et al. (1977), Bouvier-Soumagnac and Duplessy (1985), Healy-Williams et al. (1985), Schweitzer and Lohman (1991), Ravelo and Fairbanks (1995).
Distribution: In the southwestern South Atlantic (30-60°S), this species is scarce, rarely exceeding 3% of the entire foraminiferal assemblage (Boltovskoy et al., 1996). In contrast, it is abundant in the eastern South Atlantic in the area of the Walvis Ridge, especially at 21°43’S, 5°25’E, to the west of the Zaire River mouth, and at the equator. Several authors consider Globorotalia menardii a rather common member of the fauna in the tropical ocean (Jones, 1967; Bé, 1977); thus, maximum abundances at the equator are quite typical. Its high abundances above the Walvis Ridge (dominant in the cold Benguela Current) are therefore inconsistent with its tropical distribution pattern. Globorotalia menardii is very rare in sediments under the Benguela Current (Van Leeuwen, 1989). The reason for its high abundance in the water-column is not yet clear. The species might be transported by a southward-flowing subsurface current (Oberhänsli et al., 1992) because its preferred depth habitat here appears to be the lower photic zone or some 50 m deeper (e.g., 200-400 m).
As previously observed by Jones (1967), the depth distribution of Globorotalia menardii indicates affinities with the Equatorial Undercurrent, which flows along the equator at 50-100 m. Interestingly, a significant number of "living" Globorotalia menardii were found at depths of 500-1000 m. This suggests a wider depth habitat during ontogeny, as is common for deep living globorotaliids. However, expatriation phenomena may be involved in this pattern as well, as in many other species in, for example, the Red Sea, without showing the high salinity Red Sea signals in e.g. d18O (delta-18-O, or oxygen). In the western South Atlantic this species occurs in rather low numbers, seldom exceeding 3% of all foraminifers.
Remark
= Globorotalia cultrata