Denisea foramena

Denisea foramena Varol, 2022

Medium-sized circular species of Denisea have a large vacant central area with a diameter greater than or equal to twice the width of the pelaga.

From Latin foramena, area – referring to its wide, vacant area.

Maximum diameter: 8.40 μm, the diameter of the central area: 4.35 μm, the width of the pelaga: 2.06 μm; thickness: 2.06 μm.

Inclination angles of holotype: Distal shield: 63.2°; proximal shield: 63.7°; sutures between the shields: 67.3°; suture between the tube cycle and the shields: 22.0°.

Medium-sized (5.0–9.0 μm) Denisea species have a birefringent tube cycle, two shields, and a wide vacant central area. The diameter of the central area is at least twice the width of the pelaga. The separation of the tube cycle and shields is better seen in bright-field and phase-contrast illuminations.

Denisea foramena has a similar size (5.0–9.0 μm) to Denisea aliquanta and Denisea subpertusa, but their central area size makes them distinct. The central area is narrower than the width of the
pelaga in Denisea subpertusa. The diameter of the central area is at least twice the width of the pelaga in Denisea foramena. In Denisea aliquanta, the central area is greater than the width of the pelaga but not twice as much. Denisea foramena and Denisea polymegalo have vast central areas (twice the width of the pelaga). Their overall sizes set them apart; Denisea polymegalo is larger than 9.0 μm, whilst the overall size of Denisea foramena is between 5.0 and 9.0 μm.

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