Neogloboquadrina pachyderma (Ehrenberg, 1861)
Neogloboquadrina pachyderma (Fig. 33) dominates 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 preferences 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.
Neogloboquadrina pachyderma has two coiling variants which have been counted as separate categories (Fig. 34). The left-coiling (sinistral) variant is known to be frequent in cold water masses and has been found living in sea ice (e.g. Spindler, 1990). The plots of physical parameters vs. relative abundances show clearly different preferences of the two variants for sea surface temperature, salinity, and the vertical temperature gradients. In the same relative abundance range (up to 35%) the forms show comparable preferences for surface water density and stratification. Neogloboquadrina pachyderma (dextral) is a good indicator for surface water densities above about 25.5 kg/m3. Dextral coiling N. pachyderma fill in a gap best seen in the plots of relative abundance vs. sea surface temperature and surface water salinity of sinistral variants of N. pachyderma. Dextral variants can be considered as a subpopulation of N. pachyderma under suboptimum conditions.
Morphologic gradation exists between the endmembers N. pachyderma and N. dutertrei which gave rise to define intermediate species: N. incompta (Cifelli, 1961) and N. pseudopachyderma (Cita, Premoli-Silva and Rossi, 1965). CLIMAP project
members (1981) included intermediate forms in an informal group of "N.pachyderma-N. dutertrei Intergrades" (Kipp, 1976). This group is morphologically intermediate but in its relation with the physical environment it is not
intermediate: the "P-D-Intergrades" occur in subpolar environments and their preferences are nearly identical to those of N. pachyderma. Morphologic gradation in Neogloboquadrina does not indicate ecologic gradation in this group
(Hilbrecht, in press).
Figure 33: Neogloboquadrina pachyderma (Ehrenberg, 1861). Plots of relative abundance vs. selected physical parameters and latitude. For preferences in numeric form see appendix.
Figure 34: Neogloboquadrina pachyderma (Ehrenberg, 1861) differentiated for sinistral and dextral coiling forms. Plots of relative abundance vs. selected physical parameters and latitude. For preferences in numeric form see appendix.