Shining ram's-horn snail  (Segmentina nitida)

Shining ram's-horn snail

Facts

Kingdom Animalia
Phylum Mollusca
Class Gastropoda
Order Lymnophila
Family Planorbidae
Genus Segmentina (3)
Size Height: 2 mm (5)
Breadth: 5-6 mm (5)
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Status

Listed as Endangered on the GB Red List (RDB1) (2).

Description

The shining ram's-horn snail has a smooth, glossy and iridescent shell (1), measuring up to 6mm across (5), with no more than 5 whorls. The outermost whorl (body whorl) is expanded and overlaps most of the others (1), with a heart shaped aperture (1).

Range

This snail is found throughout Europe, reaching as far north as Scandinavia. In the UK it has undergone a severe decline and is now restricted to the Norfolk Broads, parts of the Kentish Stour marshes (4), and Pevensey Levels after formerly being fairly widespread throughout much of England and known from around 90 sites (2).

You can view distribution information for this species at the National Biodiversity Network GatewayDisplay NBN Map Button

Habitat

Inhabits ponds and drains of grazing marshes with unpolluted, often calcareous water, preferentially choked with a rich aquatic flora in an advanced stage of plant succession (4).

Biology

Little is known of the biology of this species.

Threats

Although the precise causes of the decline of this species are not understood, the main threats are likely to be eutrophication resulting from fertiliser run-off, ditch clearance, and conversion of grazing land to arable, and the resulting reduction in the water table (2).

Conservation

The Species Action Plan produced under the UK Biodiversity Action Plan (UK BAP) for the shining ram's-horn snail aims to promote the increase and expansion of existing populations and promote research into the ecology of the species (2).

The UK Biodiversity Action Plan for this species is available at UK Biodiversity Action Plan

Authentication

Information authenticated by Shelagh Wilson of the Environment Agency.
http://www.environment-agency.gov.uk/

Glossary

Aperture: opening in the end or area of a mollusc shell out of which soft, internal body parts may emerge.
Calcareous: containing free calcium carbonate, chalky.
Eutrophication: nutrient enrichment of aquatic or terrestrial ecosystems.
Succession: the progressive sequence of changes in vegetation types and animal life within a community that, if allowed to continue, result in the formation of a 'climax community' (the last stage in a succession where the vegetation reaches equilibrium with the environment).
Whorls: in animals, the spiral or convolutions in the shell of a snail. In plants, a set of leaves, flowers, or branches that spring from a stem at the same point and encircle it.

References

  1. The Environment Agency. (1998) Species Awareness leaflet: Snails. The Environment Agency, Bristol.
  2. UK BAP (January 2002):
    http://www.ukbap.org.uk
  3. University of Michigan. Animal Diversity Web. (January 2002):
    http://animaldiversity.ummz.umich.edu/mollusca/gastropoda/lymnophila.html
  4. A survey of the East Kent grazing marshes for the freshwater snail Segmentina nitida English Nature Research Report number 356, 2000.
  5. Wilson, S. (2002) Pers. Comm.