Morphometric evaluation of DNA-based cryptic taxa in the terrestrial decollate snail genus Rumina

Abstract

The land snail genus Rumina shows much intra- and interspecific variation in shell morphology. Three morphospecies are commonly recognized: R. decollata, R. saharica and R. paivae. The descriptions of these three morphospecies were based on differences in shell and genital characters for R. saharica and R. decollata, and shell size for R. paivae. However, recently DNA-sequence data have suggested that these morphospecies comprise at least seven phylogenetic species (R. decollata molecular operational taxonomic units (MOTUs) A –F and R. saharica). The present study explores to what extent these phylogenetic species are morphologically diagnosable and/or can be reconciled with the three currently recognized morphospecies. It shows that: (1) R. saharica, and to a lesser extent R. decollata MOTUs A and Eb, are significantly differentiated from the other phylogenetic species by both genital and shell characters, and can be regarded as three diagnosable biological and phylogenetic species; (2) there are no diagnostic genital features for R. paivae, so that this taxon should not be treated as a separate species; (3) none of the other DNA-based R. decollata MOTUs could be consistently differentiated by the shell and genital characters analysed in this study, so that their status needs further scrutiny.