MolluscIreland - land and freshwater
  • Pisidium conventus Clessin 1877 Arctic-alpine pea mussel

Map hosted by the National Biodiversity Data Centre, Waterford
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A thin, fragile shell with broad and flattened with umbos near the mid point. Surface silky with fine, concentric striation. Very rare as a relic of colder climatic periods in deep, cold, upland lakes.

Key characteristics

  • A small, thin, laterally compressed shell
  • Almost oval in shape
  • With flattened umbos near the mid-point
  • Colour yellowish-white
  • Periostracum slightly silky/glossy


2.2-2.8 mm.

World Distribution

Widely distributed in the far north of both the Palaearctic and Nearctic regions. Distribution type: Circumpolar Boreo-arctic montane (26).

GBIF distribution map [open in new tab]

Irish Distribution

Recorded only from Brandon Mountain, Kerry, Lough Barra in Donegal and Lough Aquire in Fermanagh. The only recent record is for a loughan on Brandon Mountain (Moorkens, 2005).


  • Confined to cold mountain lakes above 300m asl
  • Lives in fine muddy sediments with Littorella on the margins of a loughan on Mount Brandon

Red List status

  • Critically endangered (CR).

Wikipedia link

Wikipedia page for Pisidium conventus

 Anderson, R., (2016). Pisidium conventus Clessin 1877. [In] MolluscIreland. Accessed on 2024-03-02.