The shell of the narrow-mouthed whorl snail (Vertigo angustior) is pale yellow-brown in colour with many thin growth ridges and 5 whorls. The mouth of the shell has five to six teeth and is thickened (2). The shell is sinistral, which means the body whorls are coiled in a clockwise direction with the mouth opening on the left-hand side of the body (4).
Little is known of the biology of this species. Recent studies indicate an annual life-cycle with reproduction taking place mainly in late summer. In common with most members of the genus, the narrow-mouthed whorl snail is believed to feed on micro-fungi growing on dead and decaying plant remains (6).
This species is widely distributed but threatened in central Europe, and extends north to southern Norway and Sweden (5). The narrow-mouthed whorl snail is one of Britain's rarest land snails (5), and is currently known from just twelve scattered sites in the UK (4).
Inhabits un-shaded short, damp grass, moss or short herbs on marshes (3) or amongst leaf litter on limestone pavement (4). The largest population of the narrow-mouthed whorl snail in the UK occurs where freshwater seeps onto the margins of a saltmarsh, but in Europe the most frequent habitat is calcareous fenland (5).
Although the reasons for the rarity of this snail are not known (7), it seems that the main factors involved are the sensitivity of its habitat to changes in hydrological conditions, physical disturbance and changes in the grazing regime (3). At one site in Suffolk, shading by reed canary grass (Phalaris arundinacea) and tall herbs may have contributed to a local decline in the species (7).
The tiny narrow-mouthed whorl snail has been identified as a Priority species under the UK Biodiversity Action Plan (UK BAP). The Species Action Plan aims to maintain, protect and enhance all known populations. Three of the sites supporting this species are National Nature Reserves, a further five are designated Sites of Special Scientific Interest (SSSIs) or Areas of Scientific Interest (ASSIs). Four of the populations are designated features on candidate Special Areas of Conservation, a European site designation stemming from the EC Habitats Directive (4).
A research project funded by the Countryside Council for Wales into the ecology of this species and that of V. geyeri, another endangered snail, was completed in 2001 (8).
Cameron, R.A.D. et al. 2003. Species Accounts for snails of the genus Vertigo listed in Annex II of the Habitats Directive: V. angustior, V. genesii, V. geyeri and V. moulinsiana (Gastropoda, Pulmonata: Vertiginidae). Heldia, 5: 151-170.
National Museum & Galleries of Wales Biodiversity & Systematic Biology National Museum & Galleries of Wales Cathays Park
United Kingdom Tel: +44 (0) 2920 573244 Fax: +44 (0) 2920 239829 Harriet.Wood@nmgw.ac.uk http://www.nmgw.ac.uk
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