Melonis affinis

Melonis affinis

(Reuss, 1851)

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

Summary

Melonis affinis was a benthic foraminifer with a compact, involute calcitic test. It probably lived within or immediately on fine sea-floor sediment, extending pseudopodia from the aperture to gather bacteria, detritus and other microscopic food.

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 small, nearly planispiral involute test with a rounded periphery, inflated chambers and a symmetrical lens-like to rounded profile.

Diagnostic Features

  • Test planispiral to nearly planispiral and strongly involute.
  • Both sides are broadly similar, unlike strongly trochospiral forms.
  • Peripheral margin rounded rather than keeled.
  • Final whorl contains several gradually enlarging inflated chambers.
  • Sutures are depressed to flush and radiate toward the umbilical region.

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