Great pond clam
| Great pond clam | ||||||||||||
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Great pond clam ( Anodonta cygnea ) |
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Anodonta cygnea | ||||||||||||
| ( Linnaeus , 1758) |
The great pond mussel or pond mussel or swan mussel ( Anodonta cygnea ) belongs to the family of river and pond mussels . The great pond mussel occurs in northern and central Europe in the mud floor of standing, clean freshwater. It is endangered by increasing water pollution and is therefore, like all other species of the Unionida order , under nature protection.
features
The shell's skeleton consists of two calcareous shells that serve as protection. The shells are broad to ovoid, thin-rimmed, yellowish to dark brown. There are concentric stripes on the shell that run parallel to the growth stripes. The inside is shiny like mother-of-pearl. The mussel lock is without teeth (hence its scientific name 'Anodonta' = the edentulous one). It can grow up to 20 centimeters, and specimens with a size of 26 cm have also been found.
The pond mussel breathes through its gills. The mussel takes in water from the outside via the introducing siphon and then filters out the oxygen and food in the gills.
The mussel's nervous system consists of two nerve cords that originate centrally from a nerve node. The nerve cords contribute to locomotion and breathing. In the event of danger, the nervous system ensures that the foot, which is used for locomotion and anchoring in the ground, and the siphons are drawn in and breathing is stopped, and that the rear and front sphincters close the shells. The mussel has nerve receptors on the foot that serve the mussel for orientation and locomotion.
The mouth opening absorbs the food filtered out by the gills and passes it on to the stomach. The intestines extract the nutrients from the digested food and direct the rest to the executive siphon, the digestive gland produces digestive juices that aid digestion in the stomach. The kidney filters out toxins, the heart pumps the oxygen-rich blood to the organs, the pericardium produces a fluid that is supposed to prevent the heart from rubbing and protect it at the same time. A coat encloses all organs and protects them.
Way of life
The great pond mussel is a bottom animal and anchors itself with its foot in the soft or sandy soil. She can also move slowly with the help of her foot. It stirs up the ground and sucks in the swirled up sediment to filter out food. As a filter feeder, it cleans the water and is an important factor in the ecosystem of ponds and lakes.
The great pond clam is also attacked by parasites . It is a special host for the freshwater mite species Unionicola ypsilophora . Another species of freshwater mite , Unionicola intermedia , specifically needs the common pond mussel ( Anodonta anatina ) as a host .
The bitterling lays its eggs in the gill space of the great pond mussel, where they go through their embryonic development in a protected place and leave the mussel after about four weeks.
nutrition
The diet consists of detritus , plankton , benthic diatoms, blue algae, various green algae and microorganisms. In order to get to its food, the mussel stirs up the ground, swirls in the churned-up water, filters the food out in the gills and forwards the filtered food to the mouth opening. The filtered water is discharged through the executive siphon.
Locomotion
The great pond mussel rarely moves; then do this with her foot by stretching it out from her, pressing it into the ground and pulling the body along. Perception sensors on the foot inform the mussel about z. B. an object in the way.
Reproduction and development
The great pond clams are hermaphrodites . They produce up to 600,000 eggs which are fertilized in the gills . The brood care then takes place in the crevices between the gills. The great pond mussel is a long-term breeder. In the great pond mussel (as in all other species of pond mussels) the larvae overwinter in the gills, unlike river mussels, and are only released in early spring. The larvae already have a small two-lobed shell and live in the gills of fish (parasitic stage). This larval development as a parasite form is called glochidium . Glochidia occur only in the river mussels and river pearl mussels and thus represent a special type of development within the mussels. In the marine mussels, however, Veliger larvae are always found.
After being released into the water by the mussel, the larvae live parasitically in the skin and gills of freshwater fish . They hold on to this with a 15 mm long thread and a strong hook. When ejected from the gill space, they form slimy lumps that easily stick to fish swimming by. As soon as this has happened, the larvae separate from each other and begin to colonize the host. During this parasitic stage, the glochidia feed on the host's tissues without causing much damage. After the metamorphosis , the former larvae, which have now developed into small mussel shapes, are repelled by the host or detach themselves. The hosts include carp , but the bitterling is preferred . The great pond mussel and the bitterling live in a symbiosis: while the mussel takes in the bitterling's fish embryos, the glochidia nestle in the bitterling's. All glochidia that cannot find a host perish.
| Reproductive time | autumn |
| Residence time in the gills | over winter, as glochidia |
| Glochidia levy | January – April |
| Number of glochidia | up to 600,000 |
| Glochidia size | 0.35 mm |
| Duration of the parasitic stage | approx. 10 days to 4 weeks |
swell
- Ursula Kopp: New large animal lexicon in color. 1997, ISBN 3-8174-5080-X .
- C. Wesenberg-Lund: biology of freshwater animals. Invertebrates. Julius Springer, Vienna 1939.
- Bernhard Grzimek: Grzimeks animal life III molluscs, echinoderms. Kindler publishing house.
- Horst Füller, Hans-Eckhard Gruner, Gerhard Hartwich, Rudolf Kilias, Manfred Moritz: Urania Tierreich. Urania-Verlag, Leipzig Jena Berlin, ISBN 3-332-00502-2 .
- Wilhelm Eigener: Encyclopedia of Animals Volume 1. Manfred Pawlak Verlagsgesellschaft MBH, ISBN 3-14-508000-8 .
Individual evidence
Web links
- Anodonta cygnea inthe IUCN 2013 Red List of Threatened Species . Posted by: Vinarski, M., 2011. Retrieved February 13, 2014.
