Trachylithos nuryaziciae Varol, 2025
From the Greek trachy lithos, the rough stone – refers to its rough appearance.
The circular to elliptical placolith consists of a single-tiered distal shield, a double-tiered proximal shield, a central structure, and a double tube cycle that distally blocks the entire central area.
Optical Properties: In the plan view, the distal shield and the proximal shield’s upper tier exhibit constant extinction because their optic axis is vertical relative to the microscope stage. The tube cycles and the lower tier of the proximal shield display inclined extinction lines. In the side view, the tube cycles show length-slow (+) elongation, whereas the lower tier of the proximal shield shows length-fast (-) elongation. Observing and measuring extinction lines can be challenging.
Trachylithos differs from Toweius in that tube cycles protrude distally and block the entire central area.
Varol, O. 2025a. A practical guide to optical studies of calcareous nannofossils. Grzybowski Foundation Special Publication. 29: 1-222