Abstract The genus Pyramidula (Gastropoda: Pupilloidea) has represented one of the most taxonomically puzzling groups of Western Palaearctic micro land snails owing to a high level of morphological conservatism and shell convergence. We reconstructed Pyramidula phylogeny across the entire Western Palaearctic, using both mitochondrial (COI) and nuclear (ITS1 + ITS2) markers, based on 123 individuals from 89 localities. Unlike earlier efforts, we treated each distinct ITS indel area as a separate binary presence/absence variable that could be used as a genetic character state. Quantitative and qualitative shell features were also coded from 355 individuals sourced from genetically verified populations. Bayesian analysis and maximum likelihood both generated trees with nine well-supported species-level clades, with ITS1 + ITS2 tree resolution being notably improved at shallow phylogenetic levels through formal inclusion of indel information. Each of these clades was also found to possess distinct shell morphology and biogeography. Two are described as new species: Pyramidula koshka Horsák & Leonov sp. nov. and Pyramidula pygmaea Horsák & Kafimola sp. nov. Our results establish the first comprehensive phylogenetic framework for the genus across the Western Palaearctic. We document how indels can affect phylogenetic inference at multiple evolutionary scales and provide practical guidelines for incorporating them into Bayesian inference and maximum likelihood analyses.
Horsák et al. (Sun,) studied this question.