Furcatolithus ascella

Furcatolithus ascella Varol, in prep.

Species of Furcatolithus Martini, 1965 has a diminutive conical duolithic apical spine and a semi-open umbrella shape proximal cycle with the convex periphery.

From Latin ascella, wing - referring to its wing-like proximal cycle.

Medium size [4.0-8.0µm] species of Furcatolithus Martini,1965 having a diminutive duolithic apical spine with an axial c-axis. The duolithic apical spine is cone shape and triangular in the axial section. The proximal cycle is in a semi-open umbrella shape with a convex periphery. The opposite side of the proximal cycle is better seen at 45° and display an axial c-axis.

In crossed-polarised light, the apical spine shows maximum birefringence at 45° but extinct (dim) at 0° [the axial suture between the two helves is better seen at this orientation].

Sphenolithus ascella differs from Furcatolithus celsus (Haq 1971) Howe, 2021 by having a semi-open umbrella shape proximal cycle with a convex periphery and a diminutive non-bifurcated apical spine. The latter has a long, often bifurcating apical spine and shallow hollow frustum shape proximal cycle.

Bramlette, M. N. & Wilcoxon, J. A. 1967. Middle Tertiary calcareous nannoplankton of the Cipero section, Trinidad, W.I. Tulane Studies in Geology and Paleontology 5: 93-131.

Haq, B. U. 1971. Paleogene calcareous nannoflora. Parts I-IV. Stockholm Contributions in Geology 25: 1-158.

Howe, R., 2021. Ultrastructure and taxonomy of the family Sphenolithaceae. Journal of Nannoplankton Research 39(1), 29-75.

Martini, E. 1965. Mid-Tertiary calcareous nannoplankton from Pacific deep-sea cores. Colston Papers 17: 393-411.