Balea perversa
Encyclopedia
Balea perversa is a species
of air-breathing land snail
, a terrestrial
pulmonate gastropod mollusk in the family Clausiliidae
, the door snails. The shell of this species is left-handed in coiling and it looks like a juvenile of a clausiliid.
Balea perversa (as its synonymous name Pupa fragilis) is the type species
of the genus Balea.
It was referred from Crimea, but it was probably Mentissa gracilicosta.
is small, looks like juvenile, pale brownish, often silky shiny. It is often with distinct riblets. Apical whorls are cyclindrical. The shell has 8-9 whorls
. Last whorl is with largest diameter. It is densely ribbed. Cervix is almost without keel. Apart from a rudimentary parietalis there are no folds in the aperture
. It has no clausilium.
The width of the shell is 2.5-2.7 mm. The height of the shell is 7-10 mm.
Balea perversa differs from Balea heydeni
in its less slender and brownish rather than yellowish shell, first whorl increase in diameter less rapidly, sculpture more prominently striated (with usually distinct riblets rather than coarse growth lines).
It is easily dispersed
by birds.
It feeds on mosses, algae, lichens and cyanobacteria.
It is ovoviviparous, self-fertilization predominates, even in laboratories when snails are kept in pairs. Animals can reach maturity after 3-4 months under favourable conditions, one adult can give birth to 10-20 juveniles per year. Animals can also be active in mild winters.
It is locally threatened by too thorough and too frequent restorations of old buildings
, acid rain
s, air pollution
and cutting of old trees. It has largely disappeared from inside cities. Remains frequent in Ireland, but many colonies in lowland England have certainly disappeared, extinct around London since the 1920s.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of air-breathing land snail
Land snail
A land snail is any of the many species of snail that live on land, as opposed to those that live in salt water and fresh water. Land snails are terrestrial gastropod mollusks that have shells, It is not always an easy matter to say which species are terrestrial, because some are more or less...
, a terrestrial
Terrestrial animal
Terrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...
pulmonate gastropod mollusk in the family Clausiliidae
Clausiliidae
Clausiliidae, common name door snails, are a taxonomic family of small, very elongate, mostly left-handed, air-breathing land snails, sinistral terrestrial pulmonate gastropod mollusks....
, the door snails. The shell of this species is left-handed in coiling and it looks like a juvenile of a clausiliid.
Balea perversa (as its synonymous name Pupa fragilis) is the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
of the genus Balea.
Distribution
Distribution of this species include from Western Europe to Crimea:- British Isles: Great Britain and Ireland
- Western Europe
- Switzerland - lower concern in Switzerland
- Portugal
- Germany - vulnerable in Germany, endangered in Bavaria
- Austria - vulnerable in Austria
- Czech Republic
- on a islet near Estonia
- Sicilia
- Sardinia
- Iceland
- in Scandinavia only coastal above 62° N
It was referred from Crimea, but it was probably Mentissa gracilicosta.
Description
The shellGastropod shell
The gastropod shell is a shell which is part of the body of a gastropod or snail, one kind of mollusc. The gastropod shell is an external skeleton or exoskeleton, which serves not only for muscle attachment, but also for protection from predators and from mechanical damage...
is small, looks like juvenile, pale brownish, often silky shiny. It is often with distinct riblets. Apical whorls are cyclindrical. The shell has 8-9 whorls
Whorl (mollusc)
A whorl is a single, complete 360° revolution or turn in the spiral growth of a mollusc shell. A spiral configuration of the shell is found in of numerous gastropods, but it is also found in shelled cephalopods including Nautilus, Spirula and the large extinct subclass of cephalopods known as the...
. Last whorl is with largest diameter. It is densely ribbed. Cervix is almost without keel. Apart from a rudimentary parietalis there are no folds in the aperture
Aperture (mollusc)
The aperture is an opening in certain kinds of mollusc shells: it is the main opening of the shell, where part of the body of the animal emerges for locomotion, feeding, etc....
. It has no clausilium.
The width of the shell is 2.5-2.7 mm. The height of the shell is 7-10 mm.
Balea perversa differs from Balea heydeni
Balea heydeni
Balea heydeni is a species of air-breathing land snail, a terrestrial pulmonate gastropod mollusk in the family Clausiliidae.The shell of this species is sinistral, or left-handed in its coiling. The species has long been overlooked because of confusion with Balea perversa...
in its less slender and brownish rather than yellowish shell, first whorl increase in diameter less rapidly, sculpture more prominently striated (with usually distinct riblets rather than coarse growth lines).
Ecology
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. It lives often on surfaces encrusted with lichens and other epiphytes. It prefers trees with rough bark. It prefers shady habitats in Portugal. It may tolerate non-calcareous soils. In Bulgaria it lives up to 1600 m, perhaps 2400 m, in Switzerland up to 2000 m.It is easily dispersed
Biological dispersal
Biological dispersal refers to species movement away from an existing population or away from the parent organism. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population...
by birds.
It feeds on mosses, algae, lichens and cyanobacteria.
It is ovoviviparous, self-fertilization predominates, even in laboratories when snails are kept in pairs. Animals can reach maturity after 3-4 months under favourable conditions, one adult can give birth to 10-20 juveniles per year. Animals can also be active in mild winters.
It is locally threatened by too thorough and too frequent restorations of old buildings
Building restoration
Building restoration describes a particular treatment approach and philosophy within the field of architectural conservation. According the U.S...
, acid rain
Acid rain
Acid rain is a rain or any other form of precipitation that is unusually acidic, meaning that it possesses elevated levels of hydrogen ions . It can have harmful effects on plants, aquatic animals, and infrastructure. Acid rain is caused by emissions of carbon dioxide, sulfur dioxide and nitrogen...
s, air pollution
Air pollution
Air pollution is the introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms, or cause damage to the natural environment or built environment, into the atmosphere....
and cutting of old trees. It has largely disappeared from inside cities. Remains frequent in Ireland, but many colonies in lowland England have certainly disappeared, extinct around London since the 1920s.