Denisea constricta

Denisea constricta Varol, 2022

Large circular Denisea species have a narrow vacant central area with a diameter less than the width of the pelaga.

From Latin constricta, constricted – referring to its narrow, constricted central area.

Maximum diameter: 9.34 μm, the diameter of the central area: 2.78 μm, the width of the pelaga: 3.28 μm; thickness: 3.41 μm.

Inclination angles of holotype: Distal shield: 69.7°; proximal shield: 55.8°; sutures between the shields: 59.7°; suture between the tube cycle and the shields: 34.2°.

Large (> 9.0 μm) Denisea species have a birefringent tube cycle, two shields, and a narrow , empty central area. The diameter of the central area is equal to or less than the width of the pelaga. The separation of the tube cycle and shields is more clearly visible in bright-field and phase-contrast illuminations.

Denisea constricta, Denisea magna, and Denisea polymegalo have circular outlines and similar sizes (9.0–12.0 μm), but their central area sizes distinguish them. The central area diameter is equal to or narrower than the width of the pelaga in Denisea constricta. The diameter of the central area is at least twice the width of the pelaga in Denisea polymegalo. In Denisea magna, the central area is greater than the width of the pelaga but not twice as much. Its large size (9.0–12.0 μm) separates Denisea constricta from Denisea orbis (<5.0 μm), and from 5.0–9.0 μm in size Denisea foramena, Denisea aliquanta and Denisea subpertusa.

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