MolluscIreland - land and freshwater
  • Theodoxus (Theodoxus) fluviatilis fluviatilis (Linnaeus 1758) River Nerite
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Theodoxus (Theodoxus) fluviatilis fluviatilis
© Dr Roy Anderson

Map hosted by the National Biodiversity Data Centre, Waterford
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A small, solid shell mottled yellow or whitish on green. Has a large body whorl and large aperture closed by an operculum. Lives in hard water of lakes, canals and rivers, usually on stones or other solid support.

Key characteristics

  • A solid, dark green shell marbled and spotted with yellow or white.
  • Body whorl massive with 1-2 apical whorls perched on top.
  • Mouth wide, flattened, with a conspicuous broad white flange round the periphery to aid adhesion.
  • Operculum yellowish horn colour, thin but strong, translucent.

Size

9-13 mm

World Distribution

Ranges across Europe from the Pyrenees and Italy to coastal Finland and eastwards to the Caucasus. Distribution type: European Wide Temperate (63).

Irish Distribution

Widely distributed in central Ireland in slow-moving water or on lakeshores. It is recorded as far north-west as Glenade Lough, Sligo but is not in the Erne or Lough Neagh catchments (Kerney, 1968).

Ecology

  • Confined to well-oxygenated, usually flowing, water over calcareous bedrock
  • Also occasionally on exposed lake shores in the west
  • Prefers to settle and feed on rocks. walls or other solid support

Red List status

  • Least concern (lc).