MolluscIreland - land and freshwater
  • Balea (Balea) perversa (Linnaeus 1758) Wall snail
Click on the image to enlarge it in a new window
Balea (Balea) perversa
© Dr Roy Anderson

Map hosted by the National Biodiversity Data Centre, Waterford
To view the species profile on Biodiversity Maps and access the live map, please click on the map.

 

Very similar to Balea heydeni but outline more barrelled i.e. not evenly narrowed from base to apex, slightly fusiform. The apical whorls are in particular more cylindrical, less narrowed than in heydeni. Surface with denser more regular radial striae, slightly duller and more greyish. Generally taller with more whorls than heydeni. Aperture usually with a single parietal denticle. Mainly on rocks and walls.

Key characteristics

  • A tall-spired shell, not evenly narrowed but more cylindrical at the apex
  • Shell surface finely and evenly radially striate, dull
  • Colour greyish-brown
  • Aperture in mature shells nearly always with a single parietal denticle
  • Lip somewhat thickened, reinforced

Size

8-10 mm.

World Distribution

Distributed across western and northern Europe to Switzerland. Distribution type: Suboceanic Temperate (72).

Irish Distribution

Primarily a rupestral species i.e. on rocks and walls. Distributed across Ireland on demesne walls finished with old-fashioned lime mortar. Very localised and rare on natural rocks and probably confined to Carboniferous limestone areas.

Ecology

  • A wall species found also on natural rocks
  • Usually absent from ivied walls
  • More often on open, slightly shaded walls with epiphytic and lichen growths
  • Very few confirmed records for natural rocks

Taxonomy

It has recently emerged (Gittenberger et al. 2006) that the widespread European tree snail Balea perversa (L.) comprises two closely allied species, B. perversa s.s. and B. heydeni von Maltzan. The former occurs across Europe and has been the subject of most descriptions in the literature. The latter is smaller, has fewer whorls, is conical rather than acuminate in shape and lacks the parietal tooth typical of most populations of perversa. Perversely, this is the commoner species in Ireland. Material collected by the author and most of the material so far examined in Irish collections is referable to heydeni and perversa is seen as very local and fairly rare in Ireland.

Red List status

  • Vulnerable (VU).

Wikipedia link

Wikipedia page for Balea perversa

 Anderson, R., (2016). Balea (Balea) perversa (Linnaeus 1758). [In] MolluscIreland.
http://www.habitas.org.uk/molluscireland/species.asp?ID=42 Accessed on 2017-10-23.