Caycedoa atlanticus

Caycedoae atlanticus Bowman & Varol, 2021

A broadly elliptical species of Caycedoae having a disc and a moderate-high column. A narrow central canal characterises the column and disc.

After the Atlantic Ocean, the type area for this species is.

Column length¼6.33μm, Column width: 4.00 μm, Column height: 2.33 μm; Disc length: 11.00 μm, Disc width: 8.33 μm.

Large (7.0–11.0μm) and broadly elliptical species possessing one disc and a column. The disc is moderately wide, appears slightly concave and displays a depression on the proximal side (better seen in the side-view). The relatively high column is wide (e.g. width>height) and parallel-sided and is occupied by a narrow central canal (better seen in the side-view). The disc and column are constructed of a similar number of segments (about 22–28), and the disc segments are wider than the column segments.

The extinction lines are dextrogyre in the distal view/column side but laevogyre in the proximal view/disc side. When viewed using a gypsum plate, the horizontal axis resides within the blue sector on the distal side. In contrast, the vertical axis lies in the blue sector on the proximal side (since the species' length is oriented north-south). The column appears bright and yellowish in plan view (under polarised light). In plan view, the disc is non-birefringent, while the column is birefringent. The disc and column are birefringent in the side-view.

Caycedoa atlanticus differs from the other species of Caycedoa by appearing broadly elliptical, whereas all other species are circular. Caycedoa atlanticus possesses one disc, whereas Asinithistimorfi aubryae has two discs and displays a bizarre and rough appearance.

Bowman, A. R. & Varol, O. 2021. A Taxonomic Revision of Heliolithaceae - Applications in Resolving the Problematic Calcareous Nannofossil Biostratigraphy of the Paleocene. In: M. Montenary, M. (Ed.). Calcareous nannofossil biostratigraphy of the Stratigraphy and timescales. 6: 43-223.