Coarsely ribbed cup shell
| Coarsely ribbed cup shell | ||||||||||||
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Corbicula fluminea |
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| Scientific name | ||||||||||||
| Corbicula fluminea | ||||||||||||
| ( OV Müller , 1774) |
The coarsely ribbed cup mussel ( Corbicula fluminea ) is a freshwater mussel - a species from the family of cup mussels (Corbiculidae). It is a neozoon introduced from Southeast Asia in North America, South America, Australia and Europe . The coarsely ribbed cup mussel and the finely ribbed cup mussel ( Corbicula fluminalis ), also introduced from Asia, are generally difficult to distinguish; they are therefore often referred to collectively as Asian mussels .
features
The equally flared, strongly expanded housing is up to about 36 mm long. It is rounded-triangular in outline, only slightly longer than it is tall. The ratio of length to width to thickness is 36 mm by 33 mm by 22 mm. The vertebra, which is slightly curled forward, is small and rounded. The housings are slightly asymmetrical, the vertebrae are slightly in front of the center. The anterior dorsal side is slightly arched and slopes steeply towards the posterior end. The posterior dorsal margin is almost straight and falls even more steeply than the anterior margin towards the posterior end. The transition from the rear end to the wide ventral margin is slightly angled. The ligament lies outside and on both sides of the vertebra (amphide). The heterodontic lock has three main teeth in the left valve and one front and one rear posterior tooth. There are also three main teeth in the right valve, the two posterior teeth are doubled. The two sphincters are about the same size. The surface line is not indented.
The aragonitic shell is very thick and firm. The color of the shell can vary from ocher to dark brown on the outside; sometimes it has a slight green cast. The inside, on the other hand, is white, sometimes in combination with pale blue, rarely also pale purple and limited to smaller areas. The ornamentation consists of coarse ribs parallel to the edge (name!), Which can also be finer, especially in dark brown specimens. The periostracum is dark brown.
The foot is large and hatchet. From a size of about one millimeter, the animals develop a byssus with which they attach themselves to the hard substrate. But in the adult stage they no longer have any linen. The siphons are short and the inlet and outlet openings are surrounded by tentacles.
Differentiation of the species
The two types of cup mussels ( Corbicula ) occurring in Central Europe , the coarsely ribbed cup mussel ( Corbicula fluminea ) and the finely ribbed cup mussel ( Corbicula fluminalis ) differ in size and the fineness of the ribs. However, these traits are variable and there are obviously hybrids as well. Molecular genetic evidence has identified two genetic lines that can also hybridize (i.e., show hybrids). However, the two species remain stable overall.
Geographical distribution
Original spread
The distribution area of the coarsely ribbed cup mussel was originally Southeast Asia. The type material came from "China".
Today's distribution
The coarsely ribbed cup mussel, like the finely ribbed cup mussel, has been carried over large parts of the globe and is to be regarded as a neozoa for these regions . They were actively introduced to North America as a source of food by Asian immigrants until 1924. Apparently feral specimens were discovered in 1938. It appeared in South America in 1979.
They reached Western Europe around 1980, but it is unclear how and whether the two species were introduced at the same time. The most likely passive introduction via ballast water from ships; Targeted releasing or releasing from aquarium stocks is also conceivable.
In 1984 they were found in the Weser and in 1988 in the Netherlands in the Rhine (the mussels found at the time were already 2–3 years old). From the Netherlands they came upstream in 1991 (according to other sources in 1993) to Germany and in 1995 to Basel. From the Rhine they also reached the Main, where they spread over the Main-Danube Canal into the Danube. Using canal systems from West Germany, they also settled the Middle and East of Germany via the Weser (whose population was absorbed into it) to the Elbe and the Oder. In 2003 it was also detected in Lake Constance, and in 2007 in the Upper Rhine near Waldshut-Tiengen.
habitat
The mussels live on sandy to muddy sedimentary soils of rivers, lakes and canals. On the banks of the Rhine and other European waters, their shells can be found in huge quantities at low tide.
Reproduction and way of life
The coarsely ribbed cup mussel ( Corbicula fluminea ) is a suspension filter that filters small organisms (phytoplankton etc.) and organic detritus out of the water. Probably the main part consists of phytoplankton, since the weight gain is directly correlated with the seasons, i. H. Light and temperature. The weight gain occurred almost exclusively in the summer half of the year. Conversely, no soft body growth was observed between November and February with very low chlorophyll levels in the water.
The coarsely ribbed conch shell is a simultaneous hermaphrodite in Europe . In only 10% of the individuals, the seeds were formed before the eggs or vice versa. Sexual maturity can be reached after six months to a year. In the seven millimeter case length class, 70% of individuals already have developed sexual organs. In Hong Kong, however , the species is a protandric hermaphrodite. The small sexually mature specimens up to 9 mm in diameter were all males, while the larger specimens were exclusively females. In North America the specimens were again all simultaneous hermaphrodites. The eggs are usually fertilized by foreign seeds, but self-fertilization is also possible.
The production of sex products only starts above a temperature of 10 ° C. In the Rhine, two main spawning times could be observed, in May / June and September, although low spawning activity was also observed in June and August. The relatively large eggs are fertilized in the mantle cavity or between the gills. The eggs measure between 111 and 132 µm. After around 30 hours, the gastrulae measure 175 to 180 µm in diameter. There, the larvae develop into Trochophora larvae and Veliger larvae. They are released into the open water as Pediveliger larvae between May and September after 30 to 60 days . The water must have a temperature of more than 15 ° C. At this stage, they have a D-shaped housing about 200 to 250 µm in length and a fully functional, very large foot that is about a third of the body's mass. The velum is thrown off altogether at this stage. According to these investigations, the coarsely ribbed cup mussel ( Corbicula fluminea ) shows a certain brood care . During the reproductive phase, up to several hundred young animals per adult can be released every day, up to a total of around 8,000 per year.
Taxonomy
The taxon was set up in 1774 by Otto Friedrich Müller as Tellina fluminea . It is considered a valid taxon today.
Individual evidence
- ↑ M. Pfenninger, F. Reinhardt, B. Streit: Evidence for cryptic hybridization between different evolutionary lineages of the invasive clam genus Corbicula (Veneroida, Bivalvia). Journal of Evolutionary Biology, 15: 818-829, 2002.
- ↑ a b Otto Friedrich Müller: Vermium terrestrium et fluviatilium, seu animalium infusoriorum, helminthicorum, et testaecorum, non marinorum, succincta historia. vol. 2, pp. I-XXVI, 1-214, Havniæ / Copenhagen & Lipsiæ / Leipzig, Heineck & Faber, 1774 Online at www.biodiversitylibrary.org (p. 206)
- ↑ U. Jueg, U., ML Zettler: The mollusc fauna of the Elbe in Mecklenburg-Western Pomerania with first record of the coarsely ribbed cup mussel Corbicula fluminea ( OV Müller 1756). Communications of the Naturforschenden Gesellschaft Mecklenburg, 4 (1): 85-89, Ludwigslust 2004.
- ↑ H.-J. Wilke: First record of Corbicula fluminea in the Hohensaaten-Friedrichsthaler-Wasserstraße / Oder (Brandenburg). Lauterbornia, 59: 63-65, 2007.
- ^ O. Müller, J. Herpich, S. Rosenberger, F. Möller, N. Müller, M. Noske, K. Jähnert: Climatically limited invasion to the east? - Current distribution pattern of Corbicula fluminea in the river Oder (Brandenburg). Lauterbornia, 59: 133-139, 2007.
- ^ University of Konstanz, Department for Public Relations: New Shell in Lake Constance. ( Memento of September 5, 2005 in the Internet Archive ) Press release No. 108 of October 2, 2003, accessed on February 24, 2013
- ↑ Ryo Ishibashi, Kennichi Ookubo, Mina Aoki, Minako Utaki, Akira Komaru, Kouichi Kawamura: Androgenetic Reproduction in a Freshwater Diploid Clam Corbicula fluminea (Bivalvia: Corbiculidae). Zoological Science, 20 (6): 727-732, 2003, doi : 10.2108 / zsj.20.727
- ^ S. Rajagopal, G. van der Velde, A. bij de Vaate: Reproductive biology of the Asiatic clams Corbicula fluminalis and Corbicula fluminea in the river Rhine. Archives for Hydrobiology, 149: 403-420, 2000 ResearchGate .
- ^ L R. Kraemer, ML Galloway: Larval Development of Corbicula fluminea (Muller) (Bivalvia, Corbiculacea) - An Appraisal of Its Heterochrony. American malacological bulletin, 4: 61-79, 1986 online at www.biodiversitylibrary.org .
- ↑ MolluscaBase: Corbicula fluminea (OV Müller, 1776)