(Ehrenb.) Collen & Vella (1973: 19, pl. 1, figs 11, 12; pl. 2, figs 1–3)
Jenkins (1967b: 195–203), Kennett & Srinivasan (1983: 192, pl. 47, figs 2, 6–8), Dieckmann et al. (1991: 182)
Aristospira pachyderma Ehrenb. (Ehrenberg, 1861: 276)
Globigerina bulloides d’Orbingy var. borealis Brady (1881: 412; designated lectotype)Globigerina pachyderma (Ehrenb.) Brady (1884: 600, pl. 114, figs 19, 20)Globorotalia pachyderma (Ehrenb.) Jenkins (1967a: 1068, fig. 2; 1967b: 195)Globigerina borealis (Brady) Blow (1969: 316)
Organisms solitary, planktonic, c. 350 µm long. Test of calcite, low-trochospiral; equatorial periphery slightly lobulate; axial periphery rounded; chambers spherical to ovate, 4–4.5 chambers in the final whorl, increasing abruptly in size as added, the closely embracing final chamber irregular, often a kummerform. Sutures on spiral and umbilical sides radial, depressed; surface distinctly cancellate; thickened specimens have surface covered with euhedral calcite crystals giving a rosette pattern; umbilicus narrow, deep; aperture interiomarginal, umbilical to extraumbilical, a rather low arch with a thick apertural rim.
Southern Ocean, 63.0°S 93.57°E; bipolar (Dieckmann et al., 1991); warm-subtropical and tropical (Hillbrecht, 1996).
Neogloboquadrina pachyderma dominates foraminiferan assemblages in transitional to polar water masses and occurs in low frequencies in warm-subtropical and tropical environments. The species has broad tolerances for sea surface temperature and a preference for low sea surface salinities with little seasonal change. Its preferences for dense surface waters with low vertical temperature gradients and little stratification reflect its preferred high latitude habitats (Hilbrecht, 1996).
This species is essentially the only planktonic foraminiferan living in Antarctic waters. The foregoing description is a slight modification of that given by Kennett & Srinivasan (1983) and applies mainly to thickened adult forms. Non-thickened juveniles have the same coiling pattern, but the wall is thin and lacks the euhedral calcite rosettes so characteristic of the adults. In polar regions, the organisms are predominantly 4-chambered, sinistrally coiled morphotypes grading to 4.5-chambered, sinistral morphotypes in the sub-Antarctic, and to 4-chambered, dextral morphotypes in warmer waters. It occurs in salinities as high as 82 ppm, feed mainly on diatoms, and symbionts are not known (Hemleben et al., 1988).