Balea perversa

Balea perversa is widely distributed in western and central Europe east to Ukraine and westernmost Russia:[1]

• British Isles:[3] Great Britain and Ireland
• Western Europe[3]
• Switzerland – lower concern in Switzerland[3]
• Portugal[3]
• Germany – vulnerable in Germany, endangered in Bavaria [3]
• Austria – vulnerable in Austria[3]
• Czech Republic[4]
• Slovakia[4]
• on an islet near Estonia[5]
• Sicilia[3]
• Sardinia[3]
• Iceland[3]
• in Scandinavia only coastal above 62° N[3]

It was referred from Crimea,[3] but it was probably Mentissa gracilicosta.[5]

shells of Balea perversa

The shell is small and resembles that of a juvenile clausilid. The color is pale brownish and the surface is often silky shiny. The shell often has distinct riblets. The apical whorls are cylindrical. The shell has 8-9 whorls and (unlike many clausiliids) the last whorl has the largest diameter. It is densely ribbed. The cervix is almost without keel. Apart from a rudimentary parietal fold, there are no folds in the aperture. This species has no clausilium.[3]

The width of the shell is 2.5–2.7 mm; the height of the shell is 7–10 mm.[3]

Balea perversa differs from Balea heydeni in that it is a less slender and brownish rather than yellowish shell; the first whorl increases in diameter less rapidly, and the sculpture is more prominently striated (with what are usually distinct riblets rather than coarse growth lines).[3]

Apertural view.

Lateral view.

Balea perversa lives on mosses and at the bark of trees, also near roads, at walls and rocky slopes, at rocks, less commonly in ground litter.[3] It lives often on surfaces encrusted with lichens and other epiphytes.[3] It prefers trees with rough bark.[3] It prefers shady habitats in Portugal.[3] It may tolerate non-calcareous soils.[3] In Bulgaria it lives up to 1,600 m or perhaps to 2,400 m; in Switzerland up to 2,000 m.[3]

It is easily dispersed by birds.[3]

It feeds on mosses, algae, lichens, and cyanobacteria.[3]

It is ovoviviparous, self-fertilization predominates, even in laboratories when snails are kept in pairs.[3] Animals can reach maturity after 3–4 months under favourable conditions, one adult can give birth to 10-20 juveniles per year.[3] Animals can also be active in mild winters.[3]

It is locally threatened by too thorough and too frequent restorations of old buildings, acid rains, air pollution and cutting of old trees.[3] It has largely disappeared from inside cities.[3] Remains frequent in Ireland, but many colonies in lowland England have certainly disappeared, extinct around London since the 1920s.[3]

This article incorporates public domain text from the reference [3]

Wikimedia Commons has media related to Balea perversa.

• Balea perversa at Animalbase
• Balea perversa images at Encyclopedia of Life