Skip to Content

Special Areas of Conservation

4056 Ramshorn snail Anisus vorticulus

Invertebrate species: molluscs

Description and ecological characteristics

The Lesser whirlpool ram’s-horn snail Anisus vorticulus is a small aquatic snail with a flattened spiral shell rarely more than 5 mm in diameter. It occurs in unpolluted, calcareous waters in marsh drains with a dense aquatic flora, and favours ditches with a diverse flora but little emergent vegetation. It often floats on the surface amongst duckweed Lemna spp. Ditches that are either completely cleared of vegetation or are choked with weed and silt are unsuitable. Winter flooding may be important in enabling young snails to colonise new ditches. The main threats to the species include land drainage, inappropriate habitat management and eutrophication, and studies of its requirements and conservation management have been undertaken (Willing & Killeen 1999; Watson & Ormerod 2004).

Distribution of SACs/SCIs/cSACs with species 4056 Anisus vorticulus. Click image for enlarged map.

European status and distribution

Anisus vorticulus is mainly a central and southern European species, with a range extending as far east as Siberia. Its status in north-west Europe is poorly-known in many areas, but it is local throughout its range (Willing & Killeen 1999).

UK status and distribution

The Lesser whirlpool ram’s-horn snail Anisus vorticulus has always been a very local species in Britain. It formerly occurred at around 15 sites in south-east England, but has declined for reasons that are not fully understood, and is now restricted to a few locations in Norfolk, Suffolk and Sussex.

View UK distribution of this species.

Site selection rationale

Anisus vorticulus was added to Annex II in 2003, and no sites in the UK have yet been selected for this species.

Site accounts

  • Arun Valley Surrey, East and West Sussex
    Anisus vorticulus occurs across a range of sites in southern and eastern England. The Arun valley is one of the three main population centres for this species in the UK. This proposed site includes two of its core sites in the wash lands of the Arun floodplain (Pulborough Brooks and Amberley Wild Brooks SSSIs).
  • Pevensey Levels Surrey, East and West Sussex
    Anisus vorticulus occurs across a range of sites in southern and eastern England. Pevensey Levels is a large and expansive grazing marsh that supports Anisus vorticulus in both a wide spatial distribution and in good population density classes
  • The Broads East Anglia
    Anisus vorticulus occurs across a range of sites in southern and eastern England. The Broads is one of the three main population centres for this species in the UK.

Many designated sites are on private land: the listing of a site in these pages does not imply any right of public access.