Asinithistimorfi paraxenos Bowman & Varol, 2021
Two non-birefringent discs and a column characterize this moderate large and elliptical heliolith. The moderate-high column and plug possess a rough appearance. The extinction lines are dextrogyre in the distal view but levogyre in the proximal view. When viewed using the gypsum plate, the horizontal/short axis of the coccolith lies within the blue sector on the distal/column-side, but the vertical/long axis of the coccolith lies within the blue sector on the proximal/disc-side as the length of species is orientated in the north-south direction. In the side side-view, the median disc is slightly wider than the proximal disc, and a narrow canal may be visible in some specimens. The discs may only be observed under phase-contrast and bright-field settings (Plate 2, Figs. 20 and 24 of VBowman & Varol, 2021). In plan-view, the column and plug artificially resemble overgrown Dictyococcites under polarized light. In plan-view, the discs appear non-birefringent, whereas the column and plug appear strongly birefringent. Entire species appear birefringent in the side-view.
The bizarre rough appearance of the plug and the elliptical shape of the species are diagnostic identification features. Asinithistimorfi is distinguished from Caycedoae by the following: Asinithistimorfi is an elliptical form composed of two discs, whereas Caycedoae is circular/broadly elliptical forms consisting of one disc. In both genera, the disc(s) are non-birefringent in plan-view, separating these genera from other helioliths.
Bowman, P. 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