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Margaritifera margaritifera (Linnæus, 1758)
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Species name:
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Margaritifera margaritifera (Linnæus, 1758)
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Taxon name:
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Mya margaritifera Linnæus, 1758
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Originally described in:
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Linnæus, C. 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata. - pp. [1-4], 1-824. Holmiæ. (Salvius).
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Distribution:
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Northern Hemisphere. In Europe in Portugal, NW Spain, Bretagne, Ireland to Finland (in Norway up to 71° N), S Germany and Czech Rep.) to N Russia, E Siberia to Kamchatka and N Japan, Newfoundland to Pennsylvania
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Diagnosis:
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Shell dark brown to almost black, often with white scratches, oval elongate, embryonal whorls usually corroded, teeth strong.
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Size:
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45-60 x 100-130 x 30-40 (height) mm, maximum up to 160 mm
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Biology:
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Upper and middle sections of running oligotrophic waters, in clean and cool water free from mud and suspended matter, usually on crystalline (= soft water) and sandy substrate (only in Ireland also on calcareous substrate), often burrowed between pebbles and boulders. In Portugal often in the deepest sections of rivers.
Females produce several million glochidia (0.05 mm) which must be swallowed by a fish of the genus Salmo (Salmo salar, Salmo trutta), where they grow as gill parasites to a size of 0.5 mm. Then they leave the host and settle in the bottom of the water. They appear at the bottom surface when they have reached a size of 2 cm and an age of 4-5 years.
Average age up to 80-100 years, in Spain average 35 and maximum 65 years, in cold northern regions up to 100-190 years, maximum 210 years, belongs to the longest lived animals in the world.
One animal of 2700 contains a pearl.
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Threatened:
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Critically endangered in all parts of its range due to pollution, excessive fertilization in farmlands, habitat destruction (including soft changes such as increase of turbidity downstream by dredging), lack of hosts and destruction by pearl fishers, all in combination with its unusual longevity of 100 years or more. Only 2-3 % of the former populations are still present, often for decades without young offspring. In the Iberian peninsula restricted to Porto e Norte and Galicia and some adjacent regions, denser populations with juveniles only known from two rivers (Eo and Rabaçal). In Denmark, S France and Belgium extinct, also in most parts of Germany, Poland (only one population in SW Poland left), S Norway, Latvia, Sweden and Finland. Still fairly common in N Russia, S Ireland and Scotland, rare in Wales and N Irland, extinct in most parts of England. In Germany the last populations are protected and controlled by nature protection projects.
IUCN: Endangered (also in Spain).
Extinct in Nordrhein-Westfalen, critically endangered in Germany.
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Family:
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Margaritiferidae
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Higher group:
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Bivalvia
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Comments:
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References: Nobre 1941: 233, Clarke 1981: 248, Falkner 1990: 256, Jungbluth 1993, Vogt et al. 1994: 228, Kerney 1999: 207, Gómez Moliner et al. 2001, San Miguel et al. 2004, Velasco et al. 2006, Araujo et al. 2009: 20, Rudzīte et al. 2010: 191 (Latvia: Vidzeme region, rare), Welter-Schultes 2012: 9 (range map), Zając & Zając 2014 (Poland).
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