Description: Like the two other Anisus this has a tightly coiled flat shell of 6-7 whorls. Distinguished by being more flattened and narrow and in particular by the strong keel along the outside of the whorls towards the underside. Aperture strongly angular where the keel meets it. Widespread but declining in some areas. 7-10 mm.

World Distribution: Widespread across Europe. Distribution type: Eurosiberian Wide-temperate (64).

Irish Distribution: Mainly in the Shannon lakes and the Royal and Grand Canals of central Ireland, preferring hard water habitats or larger water-bodies. Until the nineteen-seventies it was recorded only from the Erne Basin within northern counties. In 1972 it was reported from the River Lagan near Belfast and has been found as far upstream as Hilden near Lisburn in Cos Down and Antrim (Anderson, 1977). It appears to be a recent introduction in this area. Apparently declining recently within its main Irish range in the Shannon lakes.

Ecology:

• Prefers clear, unpolluted water in larger streams, rivers and lakes.
• Usually present wherever there are rich macrophyte growths

Key Identification Features:

• A tightly coiled flat shell of 6-7 whorls
• Strongly keeled on the periphery towards the underside, the keel producing an angulate aperture
• Shell nearly opaque, light brown

Red list status:

• Vulnerable (VU).

Distribution Map from NBN: Anisus vortex at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Anisus vortex at iNaturalist World Species Observations database.

GBIF data for Anisus vortex | Classification: Gastropoda, incertae sedis, Planorbidae, Anisus

Thumbnails for genus Anisus