Denisea polymegalo

Denisea polymegalo Varol, 2022

The large circular Denisea species have a large vacant central area with a diameter equal to or twice the width of the pelaga.

From Greek polymegalo, extra-large, referring to its vast, vacant central area.

Maximum diameter: 9.90 μm, the diameter of the central area: 5.14 μm, the width of the pelaga: 2.38 μm; thickness: 3.70 μm.

Inclination angles of holotype: Distal shield: 71.9°; proximal shield: 60.8°; sutures between the shields: 61.5°; suture between the tube cycle and the shields: 23.6°.

Large (9.0–12.0 μm) circular Denisea species have a birefringent tube cycle, two shields, and a large empty central area. The diameter of the central area is at least twice the width of the pelaga. Tube cycle and shield separation are more clearly visible in bright-field and phase-contrast illuminations.

Both Denisea polymegalo and Denisea foramena have vast, empty central areas. Denisea polymegalo differs from Denisea foramena in that it is larger (>9.0 μm), whereas the latter is 5.0–9.0 μm in size. Denisea polymegalo, Denisea magna and Denisea constricta are similar in size (9.0–12.0 μm). The size of their central area makes them different. In Denisea polymegalo, the central area is vast (its diameter is at least twice the width of the pelaga). The central area diameter is also greater than the width of the pelaga in Denisea magna, but never twice as much. Denisea constricta has a narrow central area (its diameter is less than the width of the pelaga).

Varol, O. 2022. Denisea, a new genus of Paleocene calcareous nannofossils. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen, 304/2 (2022): 159-186.