Intraspecific morphological and genetic variability in Radix balthica (Linnaeus 1758) (Gastropoda: Basommatophora: Lymnaeidae) with morphological comparison to other European Radix species

Radix balthica is a morphologically very variable species that is often very difficult to determine on the basis of the shell characters. Since DNA-taxonomy is still expensive and requires much more time than anatomical determination, and the methodology is hardly available for most colleagues that work faunistically, this work aims to broaden knowledge of the intraspecific variability in the more important systematic characters used for determination of Radix balthica. To find reliable distinguishing characters from other Radix-species, an integrative approach was sought and data from three different sources were acquired for analysis. Molecular sequence data of the gene fragments ITS-2 and/or cyt—b was obtained for 58 individuals in order to study the species identity of Radix balthica (Linnaeus 1758). Of the subsample of 24 individuals for which both gene fragments were available, the variability of several characters that are commonly used for determination was documented. These include shell morphology, mantle pigmentation, shape and position of the bursa copulatrix, length and position of the bursa duct, and length ratio of praeputium to penis sheath. Morphological distinguishing characters from R. auricularia, R. labiata, R. lagotis and R. ampla are discussed and summarised in a table. Analysis of the network of haplotypes (cyt—b) shows that there is no distinct correlation to the geographic distribution pattern.