Leaning grass snail
| Leaning grass snail | ||||||||||||
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Leaning grass snail ( Vallonia excentrica ) |
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| Scientific name | ||||||||||||
| Vallonia excentrica | ||||||||||||
| Sterki , 1893 |
The leaning grass snail ( Vallonia excentrica ) is a species of land living snail from the family of grass snails (Valloniidae); the family belongs to the subordination of land snails (Stylommatophora). According to recent molecular genetic studies, the taxon is paraphyletic , i. H. there are probably two types that have a very similar housing.
features
The thick, disc-shaped casing of the crooked grass snail is 1.1 to 1.4 mm high and 2 to 2.5 mm wide. It has 2¾ to 3¼ turns that increase rapidly and regularly. The last quarter of the last turn increases particularly quickly, so that the outline of the housing is clearly egg-shaped. The first turns stand out only slightly to very little from the turn plane. The embryonic housing takes 1 1/8 turns. The turns are only slightly arched on the periphery and separated from one another by seams that are not very deep. In the cross-section, the turns embrace each other quite strongly. The last turn runs in the plane of the turn when viewed from the side, or occasionally even rises slightly. The steep and deep navel is somewhat eccentric and is comparatively very narrow; it only takes up about a quarter of the maximum case diameter. The mouth is almost round. The mouth plane is comparatively only slightly inclined. The two points of attachment of the edge of the mouth are far apart and are connected by a more or less strong, transparent or, if thick, whitish-opaque callus, which is creased in the middle towards the mouth. The actual edge of the mouth is only slightly expanded and gradually curved outwards. It is provided with a thick, ring-shaped lip on the inside, which protrudes in a bulge over the level of the mouth. The embryonic casing shows a very fine shagreening (only visible under the microscope), but is otherwise unsculpted. The Teleoconch has only irregular, smooth appearing growth strips. The surface has a waxy sheen.
The strong shell is often slightly yellow in color, otherwise milky white and transparent. The inner lip shows through the housing to the outside. In the hermaphroditic genital apparatus, the ways in which male sex products are carried out are often reduced (aphallic).
Similar species
The disc-shaped shell is similar to that of the common grass snail ( Vallonia pulchella ), but on average it is usually smaller and the last quarter of the last spiral is significantly enlarged. The outline of the housing appears elliptical.
Geographical distribution and habitat
The crooked grass snail has a huge, almost Holarctic distribution area. In the north it extends to about 60 ° north latitude, rarely further north. In Eurasia it extends in the south to the Pyrenees, northern Italy (Abruzzo), Croatia, Romania and Bulgaria, further in the east to Azerbaijan and China. In North America, the occurrence appears to be limited to the eastern parts of the United States and Canada. In Canada the species has been reported from Newfoundland, Quebec, Nova Scotia and Ontario, in the USA from the states, New York, Massachusetts, Mississippi, New Jersey, Ohio, Pennsylvania and Virginia. In the meantime it has also been anthropogenically transported to other regions (China, South Africa, Australia, New Zealand). In 2013, for example, evidence from Tasmania was published.
The species prefers cooler, open, mostly dry habitats on calcareous subsoil, such as short-growing, lawn, scree, sand dunes. As a rule, it does not occur in forests and swamps. But it tolerates less calcareous soils than z. B. Vallonia costata . In Switzerland it occurs up to 1500 m above sea level, in Bulgaria up to about 1200 m.
Reproduction
According to observations in New Zealand, where the leaning grass snail was introduced, the rare copulations only took place between euphallic specimens. The eggs were laid individually in the soil, one egg per day with a gap of several days. The juvenile animals hatched after one to two weeks (depending on the temperature). The adult size with the formation of the special mouth was reached after seven weeks. Two generations per year were formed in New Zealand. The autumn generation overwintered as not yet sexually mature animals that reached sexual maturity in spring.
Taxonomy
The taxon was recognized by Victor Sterki in 1893 as an independent taxon and already published in the form valid today ( Vallonia excentrica ). The type locality is Staten Island in the US state of New York . The lectotype determined by Henry Augustus Pilsbry in 1948 is listed in No.ANSP 10080. The validity of the taxon or the species status was discussed very controversially.
Bengt Hubendick thought the taxon was just a form or variety of Vallonia pulchella . Many authors have followed suit. Fauna Europa, Francisco Welter-Schultes and 2014 Vollrath Wiese treat the taxon as a separate species. However, according to molecular biological studies, the taxon is paraphyletic, i.e. H. there are probably two types hidden in it, which can hardly be distinguished from the morphological point of view. Only specimens from Germany were examined. Helix excentricoides Weiss, 1894 is a more recent synonym of Vallonia excentrica Sterki, 1893.
Danger
The crooked grass snail is not endangered in Germany.
supporting documents
literature
- Klaus Bogon: Land snails biology, ecology, biotope protection. Natur Verlag, Augsburg 1990, ISBN 3-89440-002-1 (pp. 140-142).
- Jochen Gerber: Revision of the genus Vallonia Risso 1826 (Mollusca: Gastropoda: Valloniidae). Schriften zur Malakozoologie, 8: 1-227, Cismar, 1996 (pp. 68-78).
- Michael P. Kerney, Robert AD Cameron & Jürgen H. Jungbluth: The land snails of Northern and Central Europe. 384 pp., Paul Parey, Hamburg & Berlin 1983, ISBN 3-490-17918-8 (p. 130)
- Francisco W. Welter-Schultes: European non-marine molluscs, a guide for species identification = identification book for European land and freshwater mollusks. A1-A3 S., 679 S., Q1-Q78 S., Planet Poster Ed., Göttingen 2012, ISBN 3-933922-75-5 , ISBN 978-3-933922-75-5 (p. 207)
Individual evidence
- ^ Gary M Barker: Naturalized terrestrial Stylommatophora (Mollusca: Gastropoda). Fauna of New Zealand, 38, 1999 online
- ^ K. Bonham: A revised list of the exotic land molluscs of Tasmania. Tasmanian Naturalist, 135: 90-97, 2013 ISSN 0819-6826
- ^ Gary M. Barker: Aspects of the biology of Vallonia excentrica (Mollusca - Vallonidae) in Waikato pastures. In: RB Chapman (Ed.), Proceedings of the 4th Australasian Conference on Grassland Invertebrate Ecology. Pp. 64-70, Christchurch, Caxton Press 1985.
- ^ Victor Sterki: Genus Vallonia Risso. (Vol. III, p. 169.) pp. 247-261, pl. 32, 33, 43, 56, in: Pilsbry, HA: Manual of conchology; structural and systematic. With illustrations of the species. Second series: Pulmonata. Vol. VIII [= 8]. Helicidæ, Vol. VI [= 6]. - pp. 1-314, pl. 1-58. Philadelphia 1893. Online at www.biodiversitylibrary.org (p. 249/50)
- ^ Henty Augustus Pilsbry: Land Mollusca of North America (North of Mexico): Mono1948 (p. 1025)
- ↑ Bengt Hubendick: On the validity of Vallonia excentrica Sterki. Proceedings of the Malacological Society, 75-78, London 1950
- ↑ a b Fauna Europaea
- ↑ a b Vollrath Wiese: The land snails of Germany. 352 pp., Quelle & Meyer, Wiebelsheim 2014 ISBN 978-3-494-01551-4 (p. 99)
- ↑ Anja Korte, Georg FJ Armbruster: Apomorphic and plesiomorphic ITS-1 rDNA patterns in morphologically similar snails (Stylommatophora: Vallonia), with estimates of divergence time. Journal of Zoology, 260 (3): 275-283, 2003 doi : 10.1017 / S0952836903003741
