MolluscIreland - land and freshwater
  • Pisidium casertanum (Poli 1791) Caserta pea mussel

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TYpically a broad, almost equilateral pea shell with broad, low umbos slightly behind the middle. Surface is silky/glossy from faint concentric striation. Colour whitish to grey-brown. Very widespread.

Key characteristics

  • A broad, sub-triangular or oval shell
  • Umbos slightly behind the middle
  • Sculpture of faint concentric striations
  • Periostracum silky, scarcely glossy
  • Colour whitish to grey-brown and often coated with reddish-brown deposits


4-5 mm.

World Distribution

With an almost cosmopolitan distribution. Distribution type: Circumpolar Wide-temperate (66).

GBIF distribution map [open in new tab]

Irish Distribution

One of the commonest Pisidium in most parts of Ireland along with P. subtruncatum.


  • Tolerant of a range of trophic conditions from lowland swamps to large, deep rivers and calcareous lakes
  • Can occur in peaty pools and swamps at high altitude
  • Usually located in bottom sediments but may climb vegetation

Red List status

  • Least concern (lc).

Wikipedia link

Wikipedia page for Pisidium casertanum

 Anderson, R., (2016). Pisidium casertanum (Poli 1791). [In] MolluscIreland. Accessed on 2024-03-02.