Sphenolithus radians Deflandre in Grassé, 1952
Sphenaster Wilcoxon, 1970.
Nannoturbella Brönnimann & Stradner 1960
Calcareous nannofossils consist of a concave base and segments radiating from a common origin, producing hexagonal patterns arranged in three cycles: the proximal, lateral and apical cycles. The morphology of the apical cycle can be classified into the following groups:
Biconical Clustered Apical Cycle – exemplified by Sphenolithus abies.
Bouquet-shaped Clustered Apical Cycle – exemplified by Sphenolithus dissimilis.
Four or More Apical Spines – exemplified by species such as Sphenolithus radians.
Monolithic Apical Spine – characterised by a single massive apical spine, exemplified by species such as Sphenolithus heteromorphus.
Multiple Apical Spines – characterised by numerous slender apical spines, as seen in Sphenolithus multispinatus.
Paired Diverging Apical Spines – characterised by a pair of apical spines that are initially parallel before diverging distally, exemplified by Sphenolithus capricornutus.
Paired Radiating Apical Spines – characterised by a well-developed pair of apical spines that radiate from a common apex and may remain parallel along their entire length, exemplified by Sphenolithus didymikoryfi.
The apical spines and the segments of lateral and proximal cycles exhibit parallel (straight) extinctions and length-fast (-) elongation when viewed from the side (Figure 16 in Varol, 2025a).
Sphenolithus differs from Furcatolithus in that segments are arranged in three cycles, whereas the segments in Furcatolithus are arranged in two cycles.
Species of Sphenolithus are identified based on their overall shape, height, width, and the construction of proximal, lateral, and apical cycles, as well as their ratios.
Brönnimann, P. & Stradner, H. 1960. Die Foraminiferen- und Discoasteriden-zonen von Kuba und ihre interkontinentale Korrelation. Erdoel-Zeitschrift 76(10): 364-369.
Deflandre, G. 1952a. Classe des Coccolithophoridés. (Coccolithophoridae. Lohmann, 1902). In: Grassé, P. P. (Ed.), Traité de Zoologie. Masson, Paris. 439-470.
Martini, E. 1965. Mid-Tertiary calcareous nannoplankton from Pacific deep-sea cores. Colston Papers 17: 393-411.
Wilcoxon, J. A. 1970. Sphenaster new genus, a Pliocene calcareous nannofossil from the tropical Indo-Pacific. Tulane Studies in Geology and Paleontology 8: 78-81.