Cibicidoides pygmeus

Cibicidoides pygmeus

(Hantken, 1875)

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

Summary

Cibicidoides pygmeus was a very small benthic cibicidid foraminifer that lived at the sediment-water interface or on firm particles. Its pseudopodial network gathered microbes and fine organic material, while the calcitic test is the structure preserved as a microfossil.

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 minute, low trochospiral planoconvex test with a rounded to subangular edge and several compact chambers in the final whorl.

Diagnostic Features

  • Test minute, trochospiral and planoconvex.
  • Spiral side relatively flat compared with the opposite side.
  • Final chambers are compact and increase gradually in size.
  • Peripheral margin rounded to weakly subangular, without a strong keel.
  • Wall is hyaline, perforate calcite with a basal interiomarginal aperture.

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