Pontosphaera japonica

Discolithina japonica Takayama 1967

Discolithina millepuncta Gartner, 1967

A Pontosphaera species exhibits nearly uniform interference colours in the plan view in XPL due to the similar height of the wall and the distal cover over the proximal plate. Pontosphaera japonica is characterised by a non-porous, wide rim and a central area densely packed with tiny pores (~0.1 μm). This species displays laevogyre-inclined extinction lines, with a typical extinction angle of approximately 68° on the distal side
and length-fast (−) elongation. Pontosphaera japonica differs from Pontosphaera decorata in having tiny, densely packed pores that are barely discernible under the light microscope. In contrast, Pontosphaera decorata exhibits less dense, relatively larger pores (~0.25 μm) that are resolvable in light microscopy.

Gartner, S. 1967a. Calcareous nannofossils from Neogene of Trinidad, Jamaica, and Gulf of Mexico. University of Kansas Paleontological Contributions, Papers 29: 1-7.

Takayama, T. 1967. First report on nannoplankton of the Upper Tertiary and Quaternary of the southern Kwanto region, Japan. Jahrbuch der Geologischen Bundesanstalt. 110: 169-198.