Cibicidoides alleni

Cibicidoides alleni

(Plummer, 1927)

Common name Foraminifer
Fossil group Foraminifera
Order Rotaliida
Family Cibicididae
Genus Cibicidoides
Taxonomic status Accepted
Geological age Ypresian

Summary

Cibicidoides alleni was an epibenthic foraminifer that lived on or just above the sea-floor surface. Its calcitic test housed a single cell whose pseudopodia spread over the substrate to gather bacteria and particulate food; related cibicidids can also attach to firm grains or shells.

The organism itself was a single cell, but the fossil is its microscopic test. In the 2026 Hampshire Basin study this taxon occurs within the London Clay Formation assemblage used to construct the first foraminiferal zonation of the formation.

Quick Identification

Look for: a low trochospiral, planoconvex to biconvex test with a rounded-to-subangular margin and clearly differentiated spiral and umbilical sides.

Diagnostic Features

  • Test trochospiral, with visibly different spiral and umbilical sides.
  • Profile low planoconvex to weakly biconvex.
  • Chambers increase regularly around the final whorl.
  • Sutures are distinct and may become gently curved toward the margin.
  • Wall is hyaline calcite and perforate; aperture occurs along the base of the final chamber.

Fossil Details

Typical size
Microscopic; generally sub-millimetric.
Fossil material
Foraminiferal Test
Preservation
London Clay foraminiferal tests may be etched, crushed, stained or filled with matrix, and the 2026 study notes poorer preservation in parts of the succession. Fine apertural and sutural characters can disappear with corrosion; incomplete tests should be left at genus or higher rank.

Similar Species

Recorded Fossil Sites

No fossil-site occurrences have yet been recorded for this species.

References

  • Hart, M. B.; Alex-Sanders, M. E. A.; Smart, C. W. (2026). Can the distribution of foraminifera locate the Early Eocene Climatic Optimum (EECO) and Middle Eocene Climatic Optimum (MECO) events in the Eocene succession of the Isle of Wight (UK)?. Journal of Micropalaeontology, 45(1), 315–334 View reference
Last Reviewed
20 August 2026 Reviewed by Sam Harris