Heliolithus kolovos

Heliolithus kolovos Bowman & Varol, 2021

A large to giant circular species of Heliolithus demonstrating a very low column that appears cut/truncated and wedge-shaped (e.g. lacks free length and does not extend above the height of the disc). The narrow canal closed with an indistinct plug/tube cycle. The disc and column are birefringent in all views.

From Greek kolovos, truncated—referring to its truncated column.

Overall height: 6.00μm; Disc diameter: 16.60μm; Column diameter: 6.07μm.

Large to very large (10.0–17.0μm) circular species constructed of one disc and a column. The disc width is much broader than the width of the column. The shallow column is slightly wider than it is higher, and the truncated appearance resembles a wedge that lacks free length or extension above the disc. The column has an indistinct, narrow central canal and a smooth plug/tube cycle and lacks the distal/proximal depressions. The disc consists of about 30–40 segments, but the column segments are indistinct.

The distal side displays dextrogyre-type extinction lines (e.g. Pl. 69, figs. 9, 13 in Bowman & Varol, 2021), and the proximal side shows laevogyre-type extinction lines (e.g. Pl. 69, figs. 11, 15 in Bowman & Varol, 2021). When observed through a gypsum plate, the horizontal axis is associated with the blue sector on the distal side. In contrast, the vertical axis resides in the blue section on the proximal side. The disc and column are birefringent in side-view and plan-view. In the side-view, the disc and column exhibit reddish-blueish birefringence, and in plan-view, the disc and column show whiteish-yellowish-orange birefringence.

This species displays variations in overall size and shape. In plan view, Heliolithus kolovos differs from the species of Caycedoa (in particular Caycedoa yelpaze) based on the diagnostic birefringent pattern of its disc. The disc is non-birefringent in plan view in the species Caycedoa. Heliolithus kolovos has a truncated/wedge-shaped column that is confined to the height of the disc (e.g. lacks free length). Heliolithus kolovos differs from other species of Heliolithus based on the following criteria: Heliolithus bukryi has a hollow column that is contrastingly higher, a distinct plug/tube cycle and a disc that displays a pointed end in side-view. Heliolithus iptamenosdiskos possesses a disc that is only slightly wider than the column (e.g. almost equal width), a smooth plug/tube cycle and a disc that exhibits rounded ends in side-view. Heliolithus knoxii has a much higher column and a very narrow central canal, and an indistinct plug/tube cycle. Heliolithus nefroeidis displays a kidney-shaped column and a narrow central canal. Heliolithus magnificus exhibits a disc that is slightly wider than the column (e.g. almost equal width), a central canal and plug/tube cycle and a disc and column that appear of similar height. Moreover, in the plan-view, Heliolithus kolovos superficially resembles Heliotrochus kleinpellii (i.e. double-disc form), but these different species may be easily distinguished through careful focusing.

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.