Tonromeinia fatmae

Tonromeinia fatmae Bowman & Varol, 2021

A large (8.0–11.0μm) circular species comprises two discs, a column of equal diameter in similar height/thickness and a large featureless central opening that lacks a tube cycle.

After Fatma Varol, North Wales, United Kingdom, administrator and inspiration at Varol Research.

Overall diameter (max) 10.3μm; Central Opening diameter 4.4μm; Discs/Column diameter 3.06μm; Discs/Column height (max) 4.75μm.

Large (8.0–11.0μm) circular species of Tonromeinia exhibiting two discs, a column and a futureless central area without a tube cycle. The discs/a column demonstrate equal diameter and similar height/ thickness. The discs and column produce a compressed character. In the side-view, the median disc may appear “wedge-shaped” at ends. Tonromeinia fatmae is generally only observed in plan-view, as the compressed behavior of the discs/column generates a concentration of mass focused along the horizontal or width-axis, which prevents specimens from settling in side-view.

Through cross-polarised light, the dextrogyre extinction lines are observed on the distal side, but the laevogyre extinction lines distinguish the proximal side. Using a gypsum plate, alignment of the horizontal axis and blue sector determines the distal side, and association of the vertical axis with the blue region indicates the proximal side. The discs and a column are birefringent in side-view and plan-view. The discs and a column show whiteish-yellowish birefringence in plan view. In the side-view, discs and a column display yellowish-brownish birefringence colours.

The diameter of the central opening is less than twice the width of the discs/column in Tonromeinia fatmae. Still, Tonromeinia davidii possesses a central opening diameter that is twice the width of the discs/column. The overall size of Tonromeinia fatmae is 8.0–11.0μm, whereas Tonromeinia bilenii is <8.0μm, and Tonromeinia deniseae is >11.0μm. Tonromeinia fatmae differs from Tonromeinia deflandrei and Tonromeinia noeliae by being circular, whereas the latter species are elliptical.

Bowman, A. R. & Varol, O. 2021. A Taxonomic Revision of Heliolithaceae - Applications in Resolving the Problematic Calcareous Nannofossil Biostratigraphy of the Paleocene. In: M. Montenary, M. (Ed.). Calcareous nannofossil biostratigraphy of the Stratigraphy and timescales. 6: 43-223.