Triquetrorhabdulus carinatus Martini, 1965
Elongate nannolith has three birefringent blades with an axial c-axis [parallel to the length of the blades]. The width of the blade various even within the same species. The surfaces of the blades may be ornamented with ridges. The blades are making equal angles to each other.
Triquetrorhabdulus is an elongated form with pointed ends composed of three blades at equal angles. In its natural settling profile, Triquetrorhabdulus displays strong birefringence and exhibits white-to-yellow interference colours. The optic axis aligns parallel to the microscope stage. Notably, Triquetrorhabdulus exhibits parallel extinction (extinction angle is 0°) and length-fast (-) elongation in its natural position, distinguishing it from Velonalithus, which has length slow (+) elongation.
Martini, E. 1965. Mid-Tertiary calcareous nannoplankton from Pacific deep-sea cores. Colston Papers 17: 393-411.
Varol, O. 2025a. A practical guide to optical studies of calcareous nannofossils. Grzybowski Foundation Special Publication. 29: 1-222