White heather snail
| White heather snail | ||||||||||||
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White heather snail ( Xerolenta obvia ) |
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| Xerolenta obvia | ||||||||||||
| Menke , 1828 |
The white heather snail ( Xerolenta obvia ), also known as the eastern heather snail , is a species of snail belonging to the Geomitridae family in the order of the pulmonary snail (Pulmonata). The species tends to be abundant.
features
The housings are medium-sized (7-10 mm high, 14-20 mm wide) with a relatively flat thread. In the adult stage there are 5 to 6 coils that increase evenly. The last turn is only very slightly lowered near the mouth compared to the turn axis of the previous passages. The seam is only weakly pronounced. The umbilicus is relatively wide and takes up about 1/4 the diameter of the case. The mouth is slightly elliptical, the mouth edges are not thickened, i. H. without lip. The mouth edge is at an angle to the axis of the coil; the lower edge is further set back.
The skin is usually thick and the basic color is white or yellowish white. Usually the individuals have very variable, dark brown to almost black bands on and under the housing periphery, but they can also be broken up into band-like spots. The surface is smooth, apart from fine and regular strips of growth.
The soft body is yellowish brown with slightly darker antennae. In the hermaphroditic genitalia, the spermatic duct enters the epiphallus at an acute angle. The flagellum is quite short, the epiphallus about twice as long as the penis. The penile retractor muscle attaches to the proximal end of the penis, almost directly at the junction of the epiphallus. Two large arrow sacks are attached to the vagina; they each contain a love arrow. The two glandulae mucosae are usually only split into four branches. The stem of the spermathec is quite long, the bladder (bursa) comes to lie in the area of the egg ladder.
Similar species
The dark brown spiral bands are usually narrower than those of the common heather snail ( Helicella itala ). The drawing is more contrasting with sharper edges of the bands. The navel is also somewhat narrower in relation to the width of the case (a quarter to a third).
Geographical distribution, habitat and way of life
The distribution area of the white heather snail extends from Asia Minor, across the Balkan Peninsula to Central Europe and the Baltic Sea. The western border in Germany is roughly on a line from Heidelberg to Lübeck. In France there are some isolated occurrences e.g. B. in the Périgord and in the Vaucluse département around Cadenet . In the Alps, the species can be found up to an altitude of 2000 m. It has now also been abducted to North America
The species lives predominantly in dry and open habitats such as steppes, dry grass slopes, vineyards, overgrown dunes, sunlit ruins, railway embankments, roadsides and loose bush vegetation, which are often exposed to very high temperatures in summer. They eat fresh, but mostly dry, plant material. The animals often go to dryness in summer and close their housing with a chalky diaphragm. In this state, they can survive months without moisture and food. They do not look for hiding places, but attach themselves to plants and stones. They can occur in huge numbers in suitable habitats.
Reproduction
The species has a one or two year reproductive cycle in northern Greece, depending on where it is located (Nea Karvali / coast or Paleokastro / mountains). Paleokastro (Chalkidiki) is located about 50 kilometers northeast of Thessaloniki at an altitude of about 600 meters above sea level. The vegetation there is dominated by grass, nettles ( Urtica dinica ), dandelions ( Taraxacum spp.) And ring thistles ( Carduus spp.). The climate is temperate, the subsoil is chalky. Nea Karvali is located 160 km northeast of Thessaloniki on the coast. The vegetation consists of grasses and dandelions.
In Paleokastro in the mountains, one generation is formed each year. The young hatched in November. In the winter months, however, they initially grew only slowly. Growth accelerated in the spring. The growth was particularly high between April and July. In July the animals were sexually mature with a shell diameter of about 8 millimeters. In summer, a rest period of two to four months was usually taken. These animals copulated in October and after a few days laid their eggs in a single clutch. Then the animals died. The animals stayed smaller.
The clutch sizes were rather small, but the eggs were on average large, as were the hatchlings (compared to Nea Karvali). The clutch contained 7 to 30 eggs (mean: 18 ± 9 eggs), the mean diameter was 1.46 mm. The hatchlings had housing sizes of 1.45 to 1.7 mm (mean: 1.58 ± 0.18 mm).
In Nea Karvali on the coast, the eggs were also laid in October. The young hatched in November. The juvenile snails reappeared from hibernation in March. There was also little growth in the winter months. They did not reach sexual maturity until April of the following year. The animals then laid their eggs in October and then died. On average, the clutches were about three times as large as in Paleokastro, but the eggs and hatchlings were significantly smaller. The clutches contained 17 to 95 eggs (mean: 57 ± 33 eggs). The eggs measured 0.9 to 1.1 mm in diameter (mean: 1 mm). The young hatched with an enclosure size of 1.0 to 1.2 mm (mean: 1.1 mm).
To lay their eggs, the snails dig a small passage at the end of which the eggs are laid. The passage is then closed with soil.
Parasites
The populations of the white heath snail are often to a high degree with cercariae of Lanzett- or small liver fluke ( Dicrocoelium dendriticum infected). The snails ingest the eggs, which contain fully developed miracidia (eyelash larvae), with their food. First order sporocysts form from the miracidia , which vegetatively develop into second order sporocysts and which in turn vegetatively produce cercaria . When the cercaria are fully developed, they migrate into the snail's respiratory cavity. The snail forms small slime balls with a diameter of up to 2 mm and traps the cercariae in the mucus. These slime balls can contain up to 400 cercariae each and are excreted from the respiratory cavity by the snail. The slime balls are eaten by ants, where the parasite further develops into metacercaria . If the ant is ingested by an ultimate host ( herbivorous mammals), the metacercariae migrate into the bile ducts and trigger dicrocoeliosis there. The snails survive the infection with the small liver fluke and can produce and excrete cercaria for two years.
The species is also an intermediate host and carrier of the sheep lungworm Protostrongylus rufescens and the tapeworm Davainea proglottina , which infects poultry. In addition, it has been proven that the animals are also carriers of spores of the mold fungi Alternaria sp., The hose fungus Fusarium sp. and the plant damaging protist genus Phytophthora sp. are. Rust fungus spores were also found in the faeces .
The white heather snail as a pest
The white heather snail ( Xerolenta obvia ) is classified as a pest in the USA and is on the list of the "New Pest Response Guidelines: Temperate Terrestrial Gastropods" of the United States Department of Agriculture. Imports are therefore checked for Xerolenta obvia and, if necessary, decontaminated. In central Montana, a colony was established in pastureland and grassland by 2013. The mucus production of the animals contaminates the hay and is no longer eaten by the animals in the barn. It is also no longer possible to sell the hay, as otherwise the white heather snail could continue to be carried away.
In Europe, it is considered a pest on forage plants such as alfalfa , clover , lupins , alfalfa and serradella . It is also classified as a pest in Italy and Bulgaria because it contaminates fruits and vegetables. Such fruits and vegetables contaminated with live snails can no longer be exported to countries that have appropriate quarantine regulations.
Taxonomy
The taxon was first introduced into scientific literature in 1828 by Karl Theodor Menke as Helix obvia . However, he only gave one indication of the wrongly determined species Helix neglecta Draparnaud, 1801 by Hartmann in Sturm (1824). Hartmann (1840) also confirmed this. The white heather snail ( Xerolenta obvia ) is the type species of the genus Xerolenta Monterosato, 1829.
The shells of the white heather snail are very variable. Therefore, the species was described under several different names: Helix candicans L. Pfeiffer, 1841, Helix dobrudschae Kobelt, 1877 (partly still accepted as a subspecies), Helix interpres Westerlund, 1879 and Helix kroli Clessin, 1879. The species was earlier often placed in the genus Helicella . Today this previously much more extensive genre is divided into several independent genres.
supporting documents
literature
- Rosina Fechter and Gerhard Falkner: molluscs. 287 p., Mosaik-Verlag, Munich 1990 (Steinbach's Nature Guide 10), ISBN 3-570-03414-3 (p. 208)
- Jürgen H. Jungbluth and Dietrich von Knorre: Common names of land and freshwater mollusks in Germany (Gastropoda et Bivalvia). Mollusca, 26 (1): 105-156, Dresden 2008 ISSN 1864-5127
- Michael P. Kerney, RAD Cameron & Jürgen H. Jungbluth: The land snails of Northern and Central Europe. 384 S., Paul Parey, Hamburg & Berlin 1983, ISBN 3-490-17918-8 (in the following abbreviated Kerney et al., Land snails with corresponding page number)
- Ewald Frömming: Biology of the Central European Landgastropods. 404 p., Duncker & Humblot, Berlin 1954 (as Helicella candicans ).
- 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., Göttingen, Planet Poster Ed., 2012 ISBN 3-933922-75-5 , ISBN 978-3-933922-75-5
- Vollrath Wiese: Germany's land snails. 352 p., Quelle & Meyer, Wiebelsheim 2014 ISBN 978-3-494-01551-4 (p. 273)
On-line
Individual evidence
- ↑ Kerney et al., Landschnecken, p. 249
- ↑ Xerolenta obvia on Invasive.org
- ↑ Maria Lazaridou, M. Chatziioannou: Differences in the life histories of Xerolenta obvia (Menke, 1828) (Hygromiidae) in a coastal and a mountainous area of Northern Greece. Journal of Molluscan Studies, 71 (3): 247-252, 2005 doi : 10.1093 / mollus / eyi032
- ↑ United States Department of Agriculture. Animal and Plant Health Inspection Service, Plant Protection and Quarantine: New Pest Response Guidelines - Temperate Terrestrial Gastropods PDF ( Memento from September 25, 2015 in the Internet Archive )
- ↑ Invasive snails affecting central Montana hay fields ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
- ^ Karl Theodor Menke: Synopsis methodica molluscorum generum omnium et specierum earum, quae in museo Menkeano adservantur; cum synonymia critica et novarum specierum diagnosibus. Pp. I-XII, 1-91, Gelpke, Pyrmont, 1828. Online at www.biodiversitylibrary.org (p. 13)
- ↑ Jacob Sturm: Germany's fauna in illustrations after nature with descriptions. VI. Division. The worms. 7th issue. Pp. 1–16, plates 1–16, Nuremberg, 1824 PDF (No. 9).
- ↑ Hartmann, JDW 1844. Earth and freshwater gasteropods of Switzerland. With the addition of some strange exotic species. I. Volume. - pp. i-xx [= 1-20], 1-227, Tab. I-XII [= 1-12], I-XII [sic, = 13-24], 25-84. St. Gallen. (Scheitlin & Zollikofer). Online at Google Books (p. 148)
