Heliolithus iptamenosdiskos

Heliolithus iptamenosdiskos Bowman and Varol, 2021

A medium to large-sized circular species of Heliolithus resembles a “flying saucer” in the side-view. The diameter of the disc is slightly greater than the column diameter, and the disc and column are of similar height, with a wide central canal closed by a plug/tube cycle.

From Greek iptamenosdiskos, flying saucer—referring to the flying saucer-like appearance of the species in side-view.

Medium to large size (6.0–10.0μm) circular species of Heliolithus consisting of one disc and a column. The diameter of the disc is often slightly wider than the diameter of the slightly tapering column , or rarely equal. The ends of the disc appear rounded in the side-view. The moderately wide canal is closed by a plug/tube cycle. Distinct depressions are present at both ends of the narrow canal [at the distal and proximal sides]. The column and disc are of similar height and appear compressed or squashed, causing the species to resemble a “flying saucer” in the side-view. The number of segments constructing the disc and column is similar (about 40), and the width of the disc segments and column segments is approximately equal.

The dextrogyre-type extinction lines are associated with the distal side (e.g. Pl. 55, figs. 9, 13 in Bowman & Varol, 2021). In contrast, the laevogyre-type extinction pattern characterises the proximal side (e.g., Pl. 55, figs. 10, 14 in Bowman & Varol, 2021). When observed using the gypsum plate, the horizontal axis corresponds to the blue region if viewed from the distal side, and the vertical axis relates to the blue sector if viewed from the proximal side. In the side-view, the disc and column are birefringent, producing a yellowish-blue birefringent colour. In plan view, the disc and column are birefringent and appear yellowish.

Heliolithus iptamenosdiskos has a column that is only fractionally narrower than the disc, a smooth plug/tube cycle, and a disc with rounded ends in its side view. In plan view, this species differs from those of Caycedoa by the diagnostic birefringent pattern of its disc. The disc is non-birefringent in plan-view in the species of Caycedoa. Critical criteria are used to compare and distinguish Heliolithus iptamenosdiskos from the following species of Heliolithus: Heliolithus bukryi possesses a hollow column that appears higher and narrower with a distinct plug/tube cycle and a disc displaying pointed ends (in the side-view). Heliolithus knoxii exhibits a much higher column that contains a very narrow central canal and an indistinct plug/tube cycle. Heliolithus nefroeidis displays a kidney-shaped column with a narrow central canal. Heliolithus kolovos demonstrates a truncated/wedge-shaped column that lacks free length (i.e. does not extend above
the height of the disc). Heliolithus magnificus has a slightly wider disc than the column, a central canal and an associated plug/tube cycle. The column lacks free length (e.g. confined to the height of the disc) and a column and disc that are of similar height. In addition, in plan-view, Heliolithus
iptamenosdiskos superficially resembles Heliotrochus kleinpellii (i.e. double-disc form), but these two 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.