Clithon pisiforme

Clithon pisiforme

(A. Férussac, 1823)

Common name Nerite
Fossil group Molluscs
Order Cycloneritida
Family Neritidae
Genus Clithon
Taxonomic status Accepted
Geological age Ypresian

Summary

Clithon pisiforme was a tiny nerite adapted to brackish marginal-water habitats. Like living nerites it would have crawled over hard surfaces, vegetation and sediment, grazing algal and microbial films.

The smooth rounded shell has a low but distinctly exserted spire and a broad semicircular aperture. Modern nomenclature treats the older form Clithon (Pictoneritina) pisiformis as an unaccepted previous combination of Clithon pisiforme.

Quick Identification

Look for: a tiny smooth glossy nerite with a rounded body whorl, a low but clearly projecting spire and a broad semicircular aperture with a wide inner lip.

Diagnostic Features

  • Shell very small, globose to pea-shaped.
  • Spire low but distinctly exserted above the body whorl.
  • Protoconch remains visible rather than being completely covered by the teleoconch.
  • Exterior smooth and glossy, without strong spiral ribs.
  • Aperture broad and semicircular with a wide flattened columellar or inner-lip area.

Fossil Details

Typical size
About 4.5 mm.
Fossil material
Shell, Internal Mould / Cast
Preservation
The robust neritid shell can survive despite its small size, but the spire and aperture edge may be chipped. Polishing can remove original surface detail and any colour pattern, so shell shape remains the primary character.

Similar Species

Recorded Fossil Sites

Synonyms & Previous Names

Clithon (Pictoneritina) pisiformis

References

  • MolluscaBase Editorial Board. (2026). MolluscaBase: Clithon pisiforme (A. Férussac, 1823). MolluscaBase View reference
  • Spijkerman, E.; van Nieulande, F. A. D.; Wesselingh, F. P.; Reich, S.; Tracey, S. (2015). Pourcy (Paris Basin, France): preliminary assessment of an early Eocene NW European tropical coastal environment from molluscs and vertebrate fossils. Cainozoic Research, 15(1–2), 155–180 View reference
  • Symonds, M. F. (2015). New species of Neritidae (Gastropoda, Neritimorpha) from the Solent Group (late Eocene and early Oligocene) of the Hampshire Basin. Cainozoic Research, 15(1–2), 147–153 View reference
Last Reviewed
22 August 2026 Reviewed by Sam Harris