Karyotypes of two European species of the genus Lymnaea with disputable taxonomic status (Gastropoda: Pulmonata: Lymnaeidae)

Karyotypes of Lymnaea corvus and L. occulta are studied for the first time and
compared to the original data on Ukrainian populations of L. palustris and L. stagnalis. While
all the studied species have the same diploid chromosome number (2n = 36), they differ in
chromosome morphology. Karyotypes of L. occulta and L. palustris include only biarmed
chromosomes (number of arms = 72). In contrast, L. corvus and L. stagnalis have also
uniarmed (acrocentric) chromosomes (number of arms = 60 and 62, respectively).
Karyological data confirm specific distinctness of L. occulta and L. corvus; however, similarity
in the chromosome morphology of the latter species to L. stagnalis is probably based on
symplesiomorphies and, thus, cannot support phylogenetic relationship suggested earlier
on the basis of anatomical characters.