Xerocrassa geyeri
Encyclopedia
Xerocrassa geyeri is a species
of air-breathing land snail
, a terrestrial
pulmonate gastropod mollusk in the family Hygromiidae
. It is also often known as Trochoidea geyeri.
(1855-1932). The type specimens are stored in the Natural History Museum of Geneva
.
is 3.4-6.0 mm, usually 3.5-5 mm. The width of the shell is 5.1(5.0)-8.0 mm.
The shell is globular in its shape. The shell has 4.5-5 whorls
. Sometimes there are radial ribs on the surface of the shell forming its shell sculpture
. There are usually no periostracal
structures, but there can in some cases be hairs and in these cases, after the hairs are gone pits remain on the shel surface especially on the whorl below the apex
. The color of the shell is greyish-white sometimes with one or a few brownish spiral bands.
of Xerocrassa geyeri was described by Gittenberger (1993): there is no appendage in the genital atrium, that is the distinguishing characteristic of the genus Xerocrassa
Monterosato, 1892. There are two rudimentary dart
-sacs near the mucus glands. The flagellum and the epiphallus have approximately the same length.
, patchy distribution. Today, the species range is mainly Central Europe
: parts of Germany
and the south of France
. Verified recent localities of Xerocrassa geyeri include:
s of a much more widespread distribution during more favourable climatic periods in the Pleistocene
era. Xerocrassa geyeri fossils are relatively abundant and Xerocrassa geyeri was one of main land snails in the western and southern Europe in glacial period
s. In loess
deposits, the presence of Xerocrassa geyeri shells has been reported since the early Pleistocene
. The subfossilised shell deposits in southern England and large parts of France are correlated with the widespread occurrence of rather arid cold steppe vegetation formations. These formations are associated with transitional phases of Pleistocene climate cycle
s, covering parts of Europe even during maximal glacial expansion
thus providing the potential for local refugia. Both Pleistocene interstadial and pleniglacial periods resulted in altitudinal and latitudinal shiftings of these formations, as well as in reductions in their extent.
The fossil record suggests that the population history of Xerocrassa geyeri is linked to palaeoclimate changes. The latitudinal shifts of suitable habitat during Pleistocene across Europe, driven by climate change, were anticipated by Xerocrassa geyeri in the fossil record with remarkably short time lags. In other words, the species can be detected in the fossil record very soon after the onset of a suitable climate phase. Research by Pfenninger et al. (2003) suggested that the origin of the species is in the Provence
from where it expanded its range first to Southwest France and subsequently from there to Germany.
Xerocrassa geyeri seems to have survived in local refugia the reduction of the favourable steppe-like habitat due to climatic extremes during the pleniglacial and interstadial periods, as it is the case today. Pfenninger & Bahl (1997) suggested that snail species with restricted dispersal might survive in habitats of a size in the magnitude of few square meters. There is increasing evidence that such small spots with a favourable microclimate existed in the periglacial area of central Europe and were presumed to have provided refuges for comparatively cold resistant snail species. Southern and eastern European refugia were also supplemented by cryptic sanctuaries in northern Europe during the late Pleistocene in shaping present day species composition.
Localities with fossil Xerocrassa geyeri are summarized in Magnin (1989) and they also include:
Xerocrassa geyeri can live only in open habitats so it died out in large areas (for example it became extinct in England) when the last glacial period ended and forests started to spread. It had to move to mountains where it survives today.
or loessic grass and scrublands with a sparse vegetation cover on mountaintops, karstic
highland plateaus and disturbed pastures, which are thought to constitute ecological refuges. In southeastern France it inhabits localities from 900 to 1000 m above sea level, but as anomaly it was found also in 370 m above sea level in Mont Vertoux.
Xerocrassa geyeri is hermaphroditic
species and fertilisation
is obligately outcrossing
. The main reproduction period is from March to June and from September to October (according table values). It lays usually less than 10 uncalcified egss, but sometimes more (according table values). Juveniles are hatching from eggs in less than two weeks (according table values). They reach sexual maturity in one year and longevity of this species is 1-2 years.
Xerocrassa geyeri feeds on dead plants, but rarely also on living plants, epilithic lichens and on algae. Its active dispersal capacity
is about 3 m during its one-year lifetime. Its competitor may be Candidula unifasciata
.
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 Hygromiidae
Hygromiidae
Hygromiidae is a taxonomic family of small to medium-sized air-breathing land snails, terrestrial pulmonate gastropod mollusks in the superfamily Helicoidea.-Anatomy:...
. It is also often known as Trochoidea geyeri.
Taxonomy
Xerocrassa geyeri was originally described under the name Xerophila geyeri by the Hungarian malacologist Lajos Soós (1879-1972) in 1926. The specific name geyeri is in honor of the German zoologist David GeyerDavid Geyer
David Geyer was German zoologist, malacologist and paleontologist.- Bibliography :Works by David Geyer were published in German language:...
(1855-1932). The type specimens are stored in the Natural History Museum of Geneva
Natural History Museum of Geneva
The Natural History Museum of Geneva is a natural history museum in Geneva, Switzerland....
.
Shell description
Xerocrassa geyeri is a small land snail. The height of 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 3.4-6.0 mm, usually 3.5-5 mm. The width of the shell is 5.1(5.0)-8.0 mm.
The shell is globular in its shape. The shell has 4.5-5 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...
. Sometimes there are radial ribs on the surface of the shell forming its shell sculpture
Sculpture (mollusc)
The sculpture of a mollusc shell is the three-dimensional ornamentation on the outer surface, as distinct from the basic shape of the shell itself or colouration. Sculpture may be concave as well as convex. Sometimes it has microscopic detail. Sculpture refers to the calcareous outer layer, not the...
. There are usually no periostracal
Periostracum
The periostracum is a thin organic coating or "skin" which is the outermost layer of the shell of many shelled animals, including mollusks and brachiopods. Among mollusks it is primarily seen in snails and clams, i.e. in bivalves and gastropods, but it is also found in cephalopods such as the...
structures, but there can in some cases be hairs and in these cases, after the hairs are gone pits remain on the shel surface especially on the whorl below the apex
Apex (mollusc)
Apex is an anatomical term for the tip of the mollusc shell of a gastropod, scaphopod, or cephalopod mollusc.-Gastropods:The word "apex" is most often used to mean the tip of the spire of the shell of a gastropod...
. The color of the shell is greyish-white sometimes with one or a few brownish spiral bands.
Anatomy
The reproductive systemReproductive system of gastropods
The reproductive system of gastropods varies greatly from one group to another within this very large and diverse taxonomic class of animals...
of Xerocrassa geyeri was described by Gittenberger (1993): there is no appendage in the genital atrium, that is the distinguishing characteristic of the genus Xerocrassa
Xerocrassa
Xerocrassa is a genus of small, air-breathing, land snails, terrestrial pulmonate gastropod molluscs in the family Hygromiidae.Some species of Xerocrassa are also referred to as belonging to the subgenus Xerocrassa, within the genus Trochoidea; those species are also known under the generic name...
Monterosato, 1892. There are two rudimentary dart
Love dart
A love dart is a hard, long, sharp, calcareous or chitinous dart which some hermaphroditic land snails and slugs create. Love darts are made in sexually mature animals only, and are used as part of the sequence of events during courtship, before actual mating takes place...
-sacs near the mucus glands. The flagellum and the epiphallus have approximately the same length.
Distribution
Xerocrassa geyeri lives in Europe, showing a discontinuousDisjunct distribution
In biology, a taxon with a disjunct distribution is one that has two or more groups that are related but widely separated from each other geographically...
, patchy distribution. Today, the species range is mainly Central Europe
Central Europe
Central Europe or alternatively Middle Europe is a region of the European continent lying between the variously defined areas of Eastern and Western Europe...
: parts of Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
and the south of France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
. Verified recent localities of Xerocrassa geyeri include:
- GotlandGotlandGotland is a county, province, municipality and diocese of Sweden; it is Sweden's largest island and the largest island in the Baltic Sea. At 3,140 square kilometers in area, the region makes up less than one percent of Sweden's total land area...
, Sweden - Belgium
- Germany. It is on the Red List of Germany: critically endangered
- Switzerland: endangered
- France
- Spain
Fossil distribution
Fossil evidence suggests that current populations of Xerocrassa geyeri are relictRelict
A relict is a surviving remnant of a natural phenomenon.* In biology a relict is an organism that at an earlier time was abundant in a large area but now occurs at only one or a few small areas....
s of a much more widespread distribution during more favourable climatic periods in the Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
era. Xerocrassa geyeri fossils are relatively abundant and Xerocrassa geyeri was one of main land snails in the western and southern Europe in glacial period
Glacial period
A glacial period is an interval of time within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate within an ice age...
s. In loess
Loess
Loess is an aeolian sediment formed by the accumulation of wind-blown silt, typically in the 20–50 micrometre size range, twenty percent or less clay and the balance equal parts sand and silt that are loosely cemented by calcium carbonate...
deposits, the presence of Xerocrassa geyeri shells has been reported since the early Pleistocene
Early Pleistocene
Calabrian is a subdivision of the Pleistocene Epoch of the Geologic time scale. ~1.8 Ma.—781,000 years ago ± 5,000 years, a period of ~.The end of the stage is defined by the last magnetic pole reversal and plunge in to an ice age and global drying possibly colder and drier than the late Miocene ...
. The subfossilised shell deposits in southern England and large parts of France are correlated with the widespread occurrence of rather arid cold steppe vegetation formations. These formations are associated with transitional phases of Pleistocene climate cycle
Climate cycle
A climate cycle is a type of recurring climate pattern that involves natural cyclic variations in the Earth's surface temperature, as indicated by temperature proxies found in glacier ice, sea bed sediment, tree ring studies or otherwise....
s, covering parts of Europe even during maximal glacial expansion
Quaternary glaciation
Quaternary glaciation, also known as the Pleistocene glaciation, the current ice age or simply the ice age, refers to the period of the last few million years in which permanent ice sheets were established in Antarctica and perhaps Greenland, and fluctuating ice sheets have occurred elsewhere...
thus providing the potential for local refugia. Both Pleistocene interstadial and pleniglacial periods resulted in altitudinal and latitudinal shiftings of these formations, as well as in reductions in their extent.
The fossil record suggests that the population history of Xerocrassa geyeri is linked to palaeoclimate changes. The latitudinal shifts of suitable habitat during Pleistocene across Europe, driven by climate change, were anticipated by Xerocrassa geyeri in the fossil record with remarkably short time lags. In other words, the species can be detected in the fossil record very soon after the onset of a suitable climate phase. Research by Pfenninger et al. (2003) suggested that the origin of the species is in the Provence
Provence
Provence ; Provençal: Provença in classical norm or Prouvènço in Mistralian norm) is a region of south eastern France on the Mediterranean adjacent to Italy. It is part of the administrative région of Provence-Alpes-Côte d'Azur...
from where it expanded its range first to Southwest France and subsequently from there to Germany.
Xerocrassa geyeri seems to have survived in local refugia the reduction of the favourable steppe-like habitat due to climatic extremes during the pleniglacial and interstadial periods, as it is the case today. Pfenninger & Bahl (1997) suggested that snail species with restricted dispersal might survive in habitats of a size in the magnitude of few square meters. There is increasing evidence that such small spots with a favourable microclimate existed in the periglacial area of central Europe and were presumed to have provided refuges for comparatively cold resistant snail species. Southern and eastern European refugia were also supplemented by cryptic sanctuaries in northern Europe during the late Pleistocene in shaping present day species composition.
Localities with fossil Xerocrassa geyeri are summarized in Magnin (1989) and they also include:
- United Kingdom:
- southeastern EnglandEnglandEngland is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
in interglacial periods: Bramertonian Stage and Cromerian Stage and in Late-Glacial - GwithianGwithianbeach2Gwithian is a coastal village in west Cornwall, United Kingdom. It is situated three miles northeast of Hayle and four miles east of St Ives, Cornwall across St Ives Bay....
in CornwallCornwallCornwall is a unitary authority and ceremonial county of England, within the United Kingdom. It is bordered to the north and west by the Celtic Sea, to the south by the English Channel, and to the east by the county of Devon, over the River Tamar. Cornwall has a population of , and covers an area of...
, south-western England in Late Postglacial in Bronze AgeBronze AgeThe Bronze Age is a period characterized by the use of copper and its alloy bronze as the chief hard materials in the manufacture of some implements and weapons. Chronologically, it stands between the Stone Age and Iron Age...
about 3070 ± 103 before presentBefore PresentBefore Present years is a time scale used in archaeology, geology, and other scientific disciplines to specify when events in the past occurred. Because the "present" time changes, standard practice is to use AD 1950 as the origin of the age scale, reflecting the fact that radiocarbon...
(1993).
- southeastern England
- France:
- Côte-d'OrCôte-d'OrCôte-d'Or is a department in the eastern part of France.- History :Côte-d'Or is one of the original 83 departments created during the French Revolution on 4 March 1790. It was formed from part of the former province of Burgundy.- Geography :...
, France in in the end of Pliocene and Burgundy, France in Early PleistoceneEarly PleistoceneCalabrian is a subdivision of the Pleistocene Epoch of the Geologic time scale. ~1.8 Ma.—781,000 years ago ± 5,000 years, a period of ~.The end of the stage is defined by the last magnetic pole reversal and plunge in to an ice age and global drying possibly colder and drier than the late Miocene ... - NormandyNormandyNormandy is a geographical region corresponding to the former Duchy of Normandy. It is in France.The continental territory covers 30,627 km² and forms the preponderant part of Normandy and roughly 5% of the territory of France. It is divided for administrative purposes into two régions:...
- CharenteCharenteCharente is a department in southwestern France, in the Poitou-Charentes region, named after the Charente River, the most important river in the department, and also the river beside which the department's two largest towns, Angoulême and Cognac, are sited.-History:Charente is one of the original...
- Côte-d'Or
Xerocrassa geyeri can live only in open habitats so it died out in large areas (for example it became extinct in England) when the last glacial period ended and forests started to spread. It had to move to mountains where it survives today.
Ecology
Xerocrassa geyeri is xerophilous species and it is found today in open calcareousCalcareous
Calcareous is an adjective meaning mostly or partly composed of calcium carbonate, in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.-In zoology:...
or loessic grass and scrublands with a sparse vegetation cover on mountaintops, karstic
Karst topography
Karst topography is a geologic formation shaped by the dissolution of a layer or layers of soluble bedrock, usually carbonate rock such as limestone or dolomite, but has also been documented for weathering resistant rocks like quartzite given the right conditions.Due to subterranean drainage, there...
highland plateaus and disturbed pastures, which are thought to constitute ecological refuges. In southeastern France it inhabits localities from 900 to 1000 m above sea level, but as anomaly it was found also in 370 m above sea level in Mont Vertoux.
Xerocrassa geyeri is hermaphroditic
Hermaphrodite
In biology, a hermaphrodite is an organism that has reproductive organs normally associated with both male and female sexes.Many taxonomic groups of animals do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which both...
species and fertilisation
Fertilisation
Fertilisation is the fusion of gametes to produce a new organism. In animals, the process involves the fusion of an ovum with a sperm, which eventually leads to the development of an embryo...
is obligately outcrossing
Outcrossing
Outcrossing is the practice of introducing unrelated genetic material into a breeding line. It increases genetic diversity, thus reducing the probability of all individuals being subject to disease or reducing genetic abnormalities...
. The main reproduction period is from March to June and from September to October (according table values). It lays usually less than 10 uncalcified egss, but sometimes more (according table values). Juveniles are hatching from eggs in less than two weeks (according table values). They reach sexual maturity in one year and longevity of this species is 1-2 years.
Xerocrassa geyeri feeds on dead plants, but rarely also on living plants, epilithic lichens and on algae. Its active dispersal capacity
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...
is about 3 m during its one-year lifetime. Its competitor may be Candidula unifasciata
Candidula unifasciata
Candidula unifasciata is a species of air-breathing land snail, a terrestrial pulmonate gastropod mollusk in the family Hygromiidae, the hairy snails and their allies.- Distribution :This species occurs in European countries and islands including:...
.
See also
Species with similar shell include:- Helicopsis striataHelicopsis striataHelicopsis striata is a species of air-breathing land snails, terrestrial pulmonate gastropod mollusks in the family Hygromiidae, the hairy snails and their allies.-Subspecies:Subspecies within this species include:...
(Müller, 1774) - Candidula unifasciataCandidula unifasciataCandidula unifasciata is a species of air-breathing land snail, a terrestrial pulmonate gastropod mollusk in the family Hygromiidae, the hairy snails and their allies.- Distribution :This species occurs in European countries and islands including:...
(Poiret, 1801)
Further reading
- Pfenninger M., Bahl A. & Streit B. (1996). "Isolation by distance in a population of a small land snail Trochoidea geyeri: Evidence from direct and indirect methods". Proceedings of the Royal Society of London Series B-Biological Sciences 263(1374): 1211-1217. doi:10.1098/rspb.1996.0178
- Prié V. (2005) "Synthèse sur la répartition de Xerocrassa geyeri (Soόs, 1926), Vertigo substriata (Jeffreys, 1833), Argna ferrari blanci (Bourguignat, 1874) et Pagodulina austeniana (Nevill, 1880) dans la marge Sud-Ouest du Massif central. [Synthesis on the distribution of Xerocrassa geyeri (Soόs, 1926), Vertigo substriataVertigo substriataVertigo substriata is a species of minute air-breathing land snail, a terrestrial pulmonate gastropod mollusk or micromollusk in the family Vertiginidae.- Distribution :The type locality is the Barnstaple district, in Devonshire, England...
(Jeffreys, 1833), Argna ferrari blanci (Bourguignat, 1874) and Pagodulina austeniana (Nevill, 1880) in the south-west margin of the Massif Central]". MalaCo, Bulletin de la Malacologie Continentale Française 1: 13-16. PDF - Falkner G., Colling M., Kittel K & Strätz C. (2003). "Rote Liste gefährdeter Schnecken und Muscheln (Mollusca) Bayerns". BayLfU/166/2003: 337-347. PDF