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.