The chromosomes of Anodonta anatina (Linnaeus, 1758) and Unio pictorum (Linnaeus, 1758) (Mollusca, Bivalvia: Unionidae)

In his paper on the male meiosis of Sphaerium corneum Keyl (1956) stated that the high chromosome numbers and relatively small nuclei make a satisfactory cytotaxonomic analysis of the Unionidae impossible. This is probably the reason that none of the European unionids has ever been studied cytotaxonomically. In view of the great phenotypical variation and complicated infraspeciation in the genera Anodonta and Unio (cf. Haas, 1940) the lack of any attempt of a cytological approach to the taxonomic problems in this family is all the more remarkable. Nevertheless, as early as 1941 Franz suggested hybridisation, serology and cytotaxonomy to be the most appropriate approaches to the problems of the inter- and infraspecific separation within these genera. So far only two workers have dealt with the cytology of the Unionidae. Lillie (1901) has studied the American species Lasmigona (Pterosyna) complanata (Rafinesque) (under the name of Unio complanata, which, incidentally, is not a synonym of the European Pseudanodonta complanata (Rossmässler, 1835)) and reported its haploid chromosome number as n = 16. Stroganova (1963) studied the spermatogenesis of Anodonta anatina (Linnaeus, 1758) (= A. piscinalis Nilsson, 1822), but did not report any chromosome numbers, nor did she publish any analysable photographs or karyograms. From her illustrations neither the karyotypic morphology nor the chromosome number of the Russian population studied, can be ascertained.