Distributional data of the Unionids in Belgium (Mollusca, Bivalvia, Unionidae)
1995
Nijs, E. | Goethem, J.L. van (Koninklijk Belgich Inst. voor Natuurwetebschappen, Brussels (Belgium). Malacology Section)
Six species of Unionidae belonging to three genera are currently found in Belgium. The shells are more or less elongate, with a high variability in some species; adult shells always exceed 4 cm in length. Diagnostic features are shape, umbonal sculpture, hinge characters and pattern of muscle scars. Unionids are mainly dioecious and ovoviviparous; the number of may be in the region of 500,000. The calcareously shelled glochidium larvae are first being brooded in the gills, which act as brood-pouches; later on, they are released as temporary parasites of fishes. The species inhabit slow rivers, canals, lowland lakes, reservoirs and ponds. For each species, a distribution map based on the UTM-grid with 10 x 10 squares km is provided. Records pre-1950 and records 1950 onwards are marked by different symbols. At present 792 records of Unionidae pre-1950 and 294 records 1950 onwards are available. This large difference does not necessarily reflect a dramatic decline of the Unionid species in Belgium, but rather seems to be due to the more intensive collecting efforts before 1950. It is suggested to take advantage of the potential ofrered by large freshwater bivalves and develop their use for nature conservation issues, especially in the field of site protection.
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