Vallonia

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Vallonia
Smooth grass snail (Vallonia pulchella)

Smooth grass snail ( Vallonia pulchella )

Systematics
Order : Lung snails (pulmonata)
Subordination : Land snails (Stylommatophora)
Superfamily : Pupilloidea
Family : Grass snails (Valloniidae)
Subfamily : Valloniinae
Genre : Vallonia
Scientific name
Vallonia
Risso , 1826

Vallonia is a genus of land-living snails from the family of grass snails (Valloniidae); the family belongs to the subordination of land snails (Stylommatophora). The oldest species of the genus comes from the Paleocene ( Palaeogene ). Some Vallonia species can occur in large numbersin suitable habitats.

features

The cases of the representatives of the genus Vallonia are small to very small. They are always wider than high and vary from flattened spherical to disc-shaped. The diameter (width) of the housing reaches 4 mm for the largest species and less than 2 mm for smaller species. The thread rises very differently from the winding plane, from truncated conical to almost level with the following windings. Only a few turns (2.6 to 4.1) are formed, each of which is separated from one another by seams of different depths, but always very clear. The dealings only slightly cover the previous dealings. The navel is wide open and funnel-shaped. The shell is very thin to firm and, depending on the thickness and the sculpture, it differs in translucence, from almost glass-like translucent to opaque. The color varies from whitish, gray-yellowish to gray-light brownish.

The muzzle plane is very oblique to the housing axis. No teeth or folds protrude into the mouth. When viewed from above, it is broader than high, broadly ovoid, elliptical or rounded and only slightly cut out due to the previous handling. The attachment points to the previous turn are connected to one another by a thin callus. The edge of the mouth is more or less widened and more or less bent outwards. The mouth rim is thickened on the inside with a swell-shaped lip.

The embryonic housing is very large compared to the overall housing. It has a shagreen- like surface with parallel raised spiral lines. However, the latter can also be almost completely reduced. The Teleoconch has ribs of different densities and different heights, but these can also be almost completely reduced. Between the ribs there are differently fine and differently dense growth strips.

The soft body is known only from a few species, but comparatively uniform in these species. When stretched out, the head and foot (without the antennae) are shorter than the diameter of the case. The sole is narrow and not divided into individual longitudinal fields. The sides of the body and back show indistinct wart-like wrinkles. When extended, the antennae measure less than a third of the length of the extended head and foot. The two lower tentacles are very short. The soft body is whitish to slightly yellowish and slightly transparent. The yellowish to light reddish brown midgut gland shines through. The radula consists of 63 to 84 transverse rows of teeth. Depending on the type, there are 23 to 35 teeth in the transverse row. The jaw is more or less strongly curved and of different widths. There are 18 to 25 low transverse ribs on the surface.

In the hermaphroditic genitalia, in most of the species that have been anatomically studied, the final male gaiters are reduced; H. Sperm ducts, penis / epiphallus with appendages are missing (= aphallic). In two anatomically examined species there are mainly aphallic specimens, but also a few specimens with fully developed male routes (= euphallic). There are also specimens in which the male exit routes are only weakly developed or are significantly smaller than in the euphallic state.

The bright hermaphroditic gland is embedded in the lower part of the midgut gland. It consists of bundles of three to four pear-shaped acini each. The hermaphroditic duct is initially thin and straight, then twisted and thickened in the middle part and more straight again in the end part. It goes into a long fertilization pouch that z. T. is embedded in the protein gland. The recesses for the intestines and the lower lobes of the midgut gland can be seen on the protein gland. The prostate lobes are located in the upper part of the egg ladder (spermoviduct). The spermatic duct (vas deferens) is slightly twisted and ends in a short epiphallus. At the transition from the epiphallus to the penis, which is significantly longer than the epiphallus, a very long, thin appendix with an elongated club-shaped thickened appendix starts. The retractor muscle splits and attaches to the epiphallus and appendix. The free fallopian tube passes into the vagina without changing its diameter; free fallopian tubes and vagina are roughly the same length. The stem of the spermathek, which attaches to the junction between free fallopian tubes and vagina, is thin, the bladder is comparatively very small.

Geographical distribution

The genus was originally distributed in the Holarctic. In the south of the Palearctic, the distribution extends to North Africa, the Middle East and Iran. Pakistan and northern India as well as southern China. In the Nearctic, the distribution extends in the south to northern Mexico. In the meantime, some species have been introduced by humans almost worldwide.

The species of the genus Vallonia are inhabitants of the open landscape without dense wood cover. They live mainly on the ground, between crumbs of earth, under leaves, wood or stones. They only climb a little on plants or walls. Vallonia cyclophorella was found in the mountain forests of southern California and northern Mexico at heights of up to 3,300 m above sea level.

Way of life

The animals reproduce predominantly, in many species even exclusively through self-fertilization. Copulations are rarely observed. The eggs are very large in relation to the size of the animals. For example, the smooth grass snail ( Vallonia pulchella ) has a diameter of 0.7 to 0.9 mm with a housing width of 2 to 2.5 mm. The eggs are laid one by one, only one egg a day, often at intervals of several days. Depending on the temperature, it only takes about two weeks from oviposition to hatching. After almost two months, the animals reach their final size and develop the characteristic mouth. Only a few days after reaching the final size, the oviposition begins, which can take several months. Then the animals die. In New Zealand, the introduced leaning grass snail ( Vallonia excentrica ) formed two generations per year in the wild. They overwinter as a juvenile form, which become sexually mature in the spring of the following year. In one species, some form of brood care has even been observed by moving the eggs from the parent and cleaning the surface. The species of the genus Vallonia feed mainly on withered plant material and fallen leaves, but fresh plant material is rarely accepted.

Taxonomy

The genus Vallonia was established in 1826 by Joseph Antoine Risso . Type species through monotype is Vallonia rosalia Risso, 1826, a more recent synonym of Helix pulchella Müller, 1774. Gerber lists the following synonyms : Amplexis Brown, 1827, Zurama Turton, 1831, Circinaria Beck, 1837, Glaphyra Albers, 1850 and Planivallonia Schileyko, 1984 as well as various misspellings of the synonymous genera. Schileyko (1998) subdivided the genus Vallonia into two sub-genera, with the sub-genera Vallonia (Vallonia) Risso, 1926 and Vallonia (Planivallonia) Schileyko, 1984. This division was followed by neither Gerber (1996) nor later authors.

The following species are currently included in the genus Vallonia (according to Gerber, 1996 with additions):

Vallonia is the type genus of the family Valloniidae and the subfamily Valloniinae Morse, 1864.

supporting documents

literature

  • Jochen Gerber: Revision of the genus Vallonia Risso 1826 (Mollusca: Gastropoda: Valloniidae). Schriften zur Malakozoologie, 8: 257 S., Cismar 1996.
  • Anatolij A. Schileyko: Treatise on Recent terrestrial pulmonate molluscs, Part 1. Achatinellidae, Amastridae, Orculidae, Strobilopsidae, Spelaeodiscidae, Valloniidae, Cochlicopidae, Pupillidae, Chondrinidae, Pyramidulidae. Ruthenica, Supplement 2 (1): 1-126, Moscow 1998 ISSN  0136-0027

Individual evidence

  1. ↑ Hartmut Nordsieck (V.2014): Annotated check-list of the genera of fossil land snails (Stylommatophora) of western and central Europe (Cretaceous - Pliocene) ( Memento of the original from July 14, 2014 in the Internet Archive ) Info: The archive link was used automatically and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.hnords.de
  2. ^ Joseph Antoine Risso: Histoire naturelle des principales productions de l'Europe méridionale et particulièrement de celles des environs de Nice et des Alpes Maritimes. Tome quatrième. P. I-VII, 1-439, Levrault, Paris, 1826 Online at www.biodiversitylibrary.org (P. 101/2)
  3. ↑ Christa Frank: About gastropod communities in central Styria cave portals. Scientific reports from the Lower Austrian State Museum, 10: 191-213, Vienna 1997 PDF
  4. ↑ a b c Jochen Gerber, Ulrich Bössneck: The genus Vallonia in Nepal: (Gastropoda: Pulmonata: Valloniidae). Archives for Molluscology (International Journal of Malacology), 138 (1): 43-52, 2009
  5. ↑ Stefan Meng, Jochen Gerber: Vallonia ranovi n sp from the Pleistocene of Southern Tajikistan Gastropoda Pulmonata Valloniidae. Journal of Conchology, 39 (5): 599-605, 2008.

On-line

Web links

Commons : Vallonia  - Collection of images, videos and audio files