Sphenolithus radians Deflandre in Grassé, 1952
Sphenaster Wilcoxon, 1970.
Nannoturbella Brönnimann & Stradner 1960
Calcareous nannofossils consist of concave base and segments spreading from a common origin, producing hexagonal patterns arranged in three cycles (proximal, lateral and apical cycle). The apical cycle can be classified into the following groups:
Well-developed Single Apical Spine: Exemplified by species such as Sphenolithus heteromorphus.
Well-developed Twin Apical Spine: These can be joined along their entire length (e.g., Sphenolithus didymikoryfi) or wholly or partly divergent (e.g., Sphenolithus capricornutus).
Well-developed multiple apical spines are seen in species like Sphenolithus multispinatus.
Clustered Apical Cycle: This can be biconical (e.g., Sphenolithus abies) or resemble a bouquet (e.g., Sphenolithus dissimilis).
Sphenolithus differs from Furcatolithus in that segments are arranged in three cycles, whereas the segments in Furcatolithus are arranged in two cycles.
Optical Properties: 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).
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.
Species with biconical clustered apical cycle
Species with a bouquet of flower-shaped, clustered apical cycles
Species with diverging/radiating apical cycle
Species with a monolithic apical spine (having parallel extinction)
Species with four or more-bladed apical spines
Species with vestigial apical cycle
Brönnimann, P. & Stradner, H. 1960. Die Foraminiferen- und Discoasteriden-zonen von Kuba und ihre interkontinentale Korrelation. Erdoel-Zeitschrift 76(10): 364-369.
Deflandre, G. 1952. 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.