Coccolithus gracejacovidesiae

Coccolithus gracejacovidesiae Varol, 2025

The circular species of Coccolithus exhibit an open central area surrounded by a non-protruding tube cycle. The proximal shield is distinctly narrower and thinner than the distal shield (comprising approximately 40 segments).

In honour of Grace Jacovides, London, United Kingdom

Diameter of distal shield = 8.61 μm; Diameter of proximal shield = 5.73 μm; Width of tube cycle = 1.12 μm; Diameter of central opening = 1.12 μm; Thickness = 3.20 μm.

Optical Properties: In the plan view, the tube cycle displays laevogyre (left-handed) extinction lines distally (Plate 10, Figs. 21-22 in Varol, 2025) and dextrogyre (right-handed) extinction lines proximally (Plate 10, Figs. 23-24 in Varol, 2025). On the tube cycle, interference colours appear as first-order white, while on the proximal shield, they appear greyish white. The tube cycle exhibits inclined extinction lines and length-fast (-) elongations. The typical extinction angle is about 85° on the tube cycle but about 74° on the distal side.

In contrast, the distal shield exhibits constant extinction (optic axis vertical relative to the microscope stage) in the plan view.

Coccolithus gracejacovidesiae differs from Coccolithus supremus in having an open central area, whereas the latter has a closed central area.

Bown, P. R. & Dunkley Jones, T. 2006. New Paleogene calcareous nannofossil taxa from coastal Tanzania: Tanzania Drilling Project Sites 11 to 14. Journal of Nannoplankton Research 28(1): 17-34.

Varol, O. 2025a. A practical guide to optical studies of calcareous nannofossils. Grzybowski Foundation Special Publication. 29: 1-222