Phylogenetic reconstruction and taxonomy of Retinella land snails: congruence and conflicts across morphological, mitochondrial, and nuclear datasets

Robust phylogenetic inference requires character data that reliably reflect evolutionary change, yet not all data streams are equally informative. We address this issue through a comparative analysis of the land snail genera Aegopinella and Retinella. Using all extant species, we contrast genital and shell morphology with three DNA datasets: mitochondrial markers, the multicopy nuclear ribosomal internal transcribed spacer (ITS) region, and two newly developed single-copy nuclear (SCN) loci. All datasets recovered well-supported, reciprocally monophyletic species-level clades, but their ability to resolve deeper relationships differed markedly. SCN data provided the most consistently resolved topology and showed the greatest congruence with independent morphological and fossil evidence. Mitochondrial data recovered a similar topology but with weaker support for deeper nodes and unresolved relationships. In contrast, ITS failed to resolve key subgeneric relationships and produce implausible divergence time estimates. Morphological traits also varied in phylogenetic utility. Genitalic characters were highly informative at the species level, whereas most shell traits were strongly homoplasious. Shell microsculpture, however, retained signal across deeper timescales. Our results support synonymizing the two genera under Retinella and the description of a new species, Retinella bodoni Bichain, Nardi & Ryelandt sp. nov., while highlighting the utility of targeted SCN loci for genus-to-species-level phylogenetic reconstruction in morphologically complex land snails.