Sub-taxa & variants (time control age-window is: 0-800Ma)![]() | ||||
| Reticulofenestra circus var. lata Very large (>12 microns), sub-circular Reticulofenestra with a medium-sized central opening with quadrate outline. | ||||
Varol (2025) suggested that R. primitiva was a senior synonym of R. circus. However, Gheta (1982) distinguished his species on the grounds that it lacked a collar around the central area and that the outer edge of the dsital shield was deflected downward. R. circus shows neither of these features.
Bown 2005 distinguished R. wadeae from R. circus based on the size of central opening, however, this criterion has not been consistently applied and there does not seem to be any evidence that central opening size changes consistently through the range of the form.
Distinguishing features:
Parent taxon (R. umbilicus group): Paleogene elliptical reticulofenestrids with open central area (spanned by delicate proximal net, not visible in lm)
This taxon: Medium-sized, subcircular Reticulofenestra with a thin tube and a medium-sized central opening with quadrate outline.
| LITHS: placolith, circular, elliptical, CA: ca_conjunct, grill, vacant, CSPH: equant, monomorphic, CROSS-POLARS: rim-unicyclic, R-prominent, |
| Lith size: 6->10µm; |
Illustrated specimens range in age from Middle Eocene to Early Oligocene.
Plot of occurrence data:
Bown, P. R. & Dunkley Jones, T. (2012). Calcareous nannofossils from the Paleogene equatorial Pacific (IODP Expedition 320 Sites U1331-1334). Journal of Nannoplankton Research. 32(2): 3-51. gs O Bown, P. R. & Newsam, C. (2017). Calcareous nannofossils from the Eocene North Atlantic Ocean (IODP Expedition 342 Sites U1403–1411). Journal of Nannoplankton Research. 37(1): 25-60. gs O Bown, P. R. (2005d). Palaeogene calcareous nannofossils from the Kilwa and Lindi areas of coastal Tanzania (Tanzania Drilling Project 2003-4). Journal of Nannoplankton Research. 27(1): 21-95. gs O De Kaenel, E. & Mojon, P. -O. (2023). Calcareous nannofossil biostratigraphy of the Eocene/Oligocene boundary (Zones NP19–21) in the parautochthonous Subalpine UMM of the Swiss Molasse Basin (Canton Fribourg, Western Switzerland). Journal of Nannoplankton Research. 41(2): 64-96. gs O de Kaenel, E. & Villa, G. (1996). Oligocene-Miocene calcareous nannofossil biostratigraphy and paleoeecology from the Iberian Abyssal Plain. Proceedings of the Ocean Drilling Program, Scientific Results. 149: 79-145. gs O Gheta, N. (1982). The Eocene of NW Transylvania. A new biochronostratigraphic zonation based on calcareous nannoplankton. Dari de Seama ale Sedintelor Institutul de Geologie si Geofizica. 69: 95-106. gs Jones, A. P. & Dunkley Jones, T. (2020). Middle Eocene to Early Oligocene calcareous nannofossils from the Nanggulan Formation, Java, Indonesia. Journal of Nannoplankton Research. 38(1): 57-79. gs Maiorano, P. (2006). Reticulofenestra circus var. lata n.var.: a large reticulofenestrid (Coccolithophoridae) from the Early Oligocene. Micropaleontology. 52(1): 81-86. gs Shepherd, C. L. & Kulhanek, D. K. (2016). Eocene nannofossil biostratigraphy of the mid-Waipara River section, Canterbury Basin, New Zealand. Journal of Nannoplankton Research. 36(1): 33-59. gs O Varol, O. (2025). A practical guide to optical studies of calcareous nannofossils. Grzybowski Foundation Special Publication. 29: 1-222. gsReferences:

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Reticulofenestra circus compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 22-7-2026
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