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Unio crassus Philipsson, 1788
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Species name:
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Unio crassus Philipsson, 1788
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Taxon name:
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Unio Crassus Philipsson, 1788
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Originally described in:
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Retzius, A. J. 1788. Dissertatio historico-naturalis sistens nova testaceorum genera. Quam præside D. M. Andr. J. Retzio (...) ad publicum examen defert Laurentius Münter Philipsson. - pp. [1-4], 1-23. Lundæ. (Dissertatio Historico-Naturalis). (Berling).
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Distribution:
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Europe except Iberian peninsula and British Isles, to Black Sea region and Iraq
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Diagnosis:
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Shell very dark, almost black, sometimes with greenish streaks, short and elliptical (posterior margin on upper side rounded, not straight), most solid parts located behind the embryonic shell, which is usually corroded, lower margin straight, not curved, the main tooth is steeply conical and pointed.
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Size:
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25-45 x 40-70 x 20-28 (height) mm
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Biology:
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In clean rivers (prefers their middle sections) and smaller running waters, in the SE also at lake margins. In sandy and stony substrate, usually entirely inside, not in contaminated muddy substrate. Confined to lowlands, highest records in the past in Switzerland from up to 600 m.
Juveniles are extremely sensitive against any kind of water pollution and need high oxygen contents, adults cannot reproduce in running waters with nitrate contents exceeding 10 mg/l. Life span 20-30 years. Sexes are separate, high population densities are needed for reproduction.
Gill parasite of some fishes, hosts are Cottus gobio, Phoxinus phoxinus, Leuciscus cephalus, Scardinius erythrophthalmus, Gymnocephalus cernua and Perca fluviatilis, in N Germany also Gasterosteus aculeatus. Different populations may have different fish hosts, sometimes only some local populations of fishes can serve as hosts.
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Threatened:
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Until the 1950s the most frequent freshwater bivalve of Europe, it was collected in high numbers in the vicinity of villages and was widely used as food for pigs and chicken. It first disappeared from rivers, later also from smaller running waters. Today shortly before extinction, more threatened than Margaritifera margaritifera. In many relictual populations there have been no juveniles since before 1980. Threatened by water pollution, drainage, regulations of small running waters and disappearing of host fish species. In some regions findings of Unio crassus have the potential to stop industrial projects.
IUCN: Endangered. Critically endangered in Germany, Switzerland (already vanished from most Cantons) and Austria, vulnerable in Albania.
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Family:
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Unionidae
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Higher group:
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Bivalvia
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Comments:
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Populations from Spain and Portugal were recently classified as Unio tumidiformis based on molecular studies (Araujo et al. 2009: 49).
References: Geyer 1927, Reischütz & R. 2003: 29 (Etoloakarnania, lakes Trichonia and Lisimachia), Falkner 1990: 260, Jungbluth 1993, Vogt et al. 1994: 231, Turner et al. 1998: 383, Gómez Moliner et al. 2001, Dhora 2004: 143, Glöer & Diercking 2010: 128, Welter-Schultes 2012: 12 (range map Europe).
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