Morphology and taxonomic assessment of eight genetic clades of Mercuria Boeters, 1971 (Caenogastropoda, Hydrobiidae), with the description of five new species

Abstract

The freshwater snail genus Mercuria is widely distributed in lowland waters across Western Europe, Northern Africa and the Mediterranean islands. Approximately two-thirds of the currently recognised species are described based on their shell morphology, which may vary within species due to biotic and abiotic factors. Recent molecular phylogenies that included numerous previously documented populations recovered 14 species clades, nine of which correspond to nominal species and five, to undescribed taxa. Here, we formally describe the five undescribed taxa as new species and provide morphological descriptions of the shell and other anatomical structures for three of the other inferred clades and for the species M. maceana to elucidate their taxonomic status and assess the utility of morphological characters for species delimitation in Mercuria. Taken together, the morphological and molecular evidence suggest new identifications and synonymies, having implications on the known geographic range of the studied species, including the type species M. similis. Anatomical measurements and geometric morphometric analysis of shell shape revealed no clear differentiation among the species analysed, predicting the importance of molecular data in elucidating the species diversity of the genus.

A practical, step-by-step, guide to taxonomic comparisons using Procrustes geometric morphometrics and user-friendly software (part A): introduction and preliminary analyses

“…For taxonomic assessment, GMM rarely provides conclusive evidence on its own, but it offers a low cost and relatively simple tool for exploratory studies and phenotypic analyses complimentary to genetics . Indeed, GMM analyses, often combined with molecular data, have become common in journals specifically devoted to taxonomy, such as the European Journal of Taxonomy, Zookeys and Zootaxa (e.g., in gerbils (Yazdi et al 2014), lizards (Marín et al 2016), fish (Craig et al 2017), snails (Perez et al 2021;Whelan et al 2023;Miller et al 2023), wasps (Schwarzfeld & Sperling 2014), fossil bees (Dehon et al 2019), fruit flies (Hendrichs et al 2015), beetles (Qubaiová et al 2015;Su et al 2015;Sasakawa 2016), hemipterans (Armendáriz-Toledano et al 2023), spiders (Valdez-Mondragón et al 2019), and centipedes (Gutierrez et al 2011)).…”